Merge branches 'expcb.2026.07.24a', 'misc.2026.07.30a', 'rcu-tasks.2026.07.30a', 'srcu.2026.08.11a' and 'torture.2026.08.14a' into HEADgrafted

Changes:

Make expedited grace periods expedite normal RCU callbacks

Miscellaneous fixes:
 * Improve diagnostic output with character task states.
 * Mark accesses to inform KCSAN of concurrency design.
 * Move from kmalloc() to kmalloc_obj().
 * Documentation updates.
 * Improve handling of RCU deferred quiescent states.
 * Clean up unused function arguments and structure fields.
 * Reduce show_rcu_gp_kthreads() stack space.

Tasks RCU updates:
 * Clean up after SRCU re-implementation of Tasks Trace RCU.
 * Mark accesses to inform KCSAN of concurrency design.
 * Add ->lazy_timer status to diagnostic output.
 * Remove an unnecessary memory barrier.
 * Fix a data race, courtesy of KCSAN.
 * Documentation updates.
 * Convert cond_resched_tasks_rcu_qs() from macro to static inline
   function.

SRCU updates:
 * Add Rust helpers for SRCU.
 * Avoid losing queued work at cleanup_srcu_struct() time.

Torture-test updates:
 * Preparation work for immediate RCU priority deboosting.
 * Test RCU readers from real interrupt handlers (as opposed to softirq).
 * Simplify code through use of cpumask_next_wrap().
 * Improve diagnostic output with character task states.
 * Add rcutorture.nwriters parameter to allow lightweight stall testing,
   and rcutorture.stall_only to make doing so easier.
 * Test an RCU Tasks Trace grace period implying an RCU grace period.
 * Make RCU Tasks Trace torturing track reader batches.
 * Fix a data race, courtesy of KCSAN.
 * Plug a shuffle_tmp_mask memory leak on kthread spawn failure.

1 files changed, 1047 insertions, 0 deletions

diff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c
new file mode 100644
index 000000000..84349fcb9
--- /dev/null
+++ b/fs/binfmt_misc.c
@@ -0,0 +1,1047 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * binfmt_misc.c
+ *
+ * Copyright (C) 1997 Richard Günther
+ *
+ * binfmt_misc detects binaries via a magic or filename extension and invokes
+ * a specified wrapper. See Documentation/admin-guide/binfmt-misc.rst for more details.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/hex.h>
+#include <linux/init.h>
+#include <linux/sched/mm.h>
+#include <linux/magic.h>
+#include <linux/binfmts.h>
+#include <linux/slab.h>
+#include <linux/ctype.h>
+#include <linux/string_helpers.h>
+#include <linux/file.h>
+#include <linux/pagemap.h>
+#include <linux/namei.h>
+#include <linux/mount.h>
+#include <linux/fs_context.h>
+#include <linux/syscalls.h>
+#include <linux/fs.h>
+#include <linux/uaccess.h>
+
+#include "internal.h"
+
+#ifdef DEBUG
+# define USE_DEBUG 1
+#else
+# define USE_DEBUG 0
+#endif
+
+enum {
+	VERBOSE_STATUS = 1 /* make it zero to save 400 bytes kernel memory */
+};
+
+enum {Enabled, Magic};
+#define MISC_FMT_PRESERVE_ARGV0 (1UL << 31)
+#define MISC_FMT_OPEN_BINARY (1UL << 30)
+#define MISC_FMT_CREDENTIALS (1UL << 29)
+#define MISC_FMT_OPEN_FILE (1UL << 28)
+
+typedef struct {
+	struct list_head list;
+	unsigned long flags;		/* type, status, etc. */
+	int offset;			/* offset of magic */
+	int size;			/* size of magic/mask */
+	char *magic;			/* magic or filename extension */
+	char *mask;			/* mask, NULL for exact match */
+	const char *interpreter;	/* filename of interpreter */
+	char *name;
+	struct dentry *dentry;
+	struct file *interp_file;
+	refcount_t users;		/* sync removal with load_misc_binary() */
+} Node;
+
+static struct file_system_type bm_fs_type;
+
+/*
+ * Max length of the register string.  Determined by:
+ *  - 7 delimiters
+ *  - name:   ~50 bytes
+ *  - type:   1 byte
+ *  - offset: 3 bytes (has to be smaller than BINPRM_BUF_SIZE)
+ *  - magic:  128 bytes (512 in escaped form)
+ *  - mask:   128 bytes (512 in escaped form)
+ *  - interp: ~50 bytes
+ *  - flags:  5 bytes
+ * Round that up a bit, and then back off to hold the internal data
+ * (like struct Node).
+ */
+#define MAX_REGISTER_LENGTH 1920
+
+/**
+ * search_binfmt_handler - search for a binary handler for @bprm
+ * @misc: handle to binfmt_misc instance
+ * @bprm: binary for which we are looking for a handler
+ *
+ * Search for a binary type handler for @bprm in the list of registered binary
+ * type handlers.
+ *
+ * Return: binary type list entry on success, NULL on failure
+ */
+static Node *search_binfmt_handler(struct binfmt_misc *misc,
+				   struct linux_binprm *bprm)
+{
+	char *p = strrchr(bprm->interp, '.');
+	Node *e;
+
+	/* Walk all the registered handlers. */
+	list_for_each_entry(e, &misc->entries, list) {
+		char *s;
+		int j;
+
+		/* Make sure this one is currently enabled. */
+		if (!test_bit(Enabled, &e->flags))
+			continue;
+
+		/* Do matching based on extension if applicable. */
+		if (!test_bit(Magic, &e->flags)) {
+			if (p && !strcmp(e->magic, p + 1))
+				return e;
+			continue;
+		}
+
+		/* Do matching based on magic & mask. */
+		s = bprm->buf + e->offset;
+		if (e->mask) {
+			for (j = 0; j < e->size; j++)
+				if ((*s++ ^ e->magic[j]) & e->mask[j])
+					break;
+		} else {
+			for (j = 0; j < e->size; j++)
+				if ((*s++ ^ e->magic[j]))
+					break;
+		}
+		if (j == e->size)
+			return e;
+	}
+
+	return NULL;
+}
+
+/**
+ * get_binfmt_handler - try to find a binary type handler
+ * @misc: handle to binfmt_misc instance
+ * @bprm: binary for which we are looking for a handler
+ *
+ * Try to find a binfmt handler for the binary type. If one is found take a
+ * reference to protect against removal via bm_{entry,status}_write().
+ *
+ * Return: binary type list entry on success, NULL on failure
+ */
+static Node *get_binfmt_handler(struct binfmt_misc *misc,
+				struct linux_binprm *bprm)
+{
+	Node *e;
+
+	read_lock(&misc->entries_lock);
+	e = search_binfmt_handler(misc, bprm);
+	if (e)
+		refcount_inc(&e->users);
+	read_unlock(&misc->entries_lock);
+	return e;
+}
+
+/**
+ * put_binfmt_handler - put binary handler node
+ * @e: node to put
+ *
+ * Free node syncing with load_misc_binary() and defer final free to
+ * load_misc_binary() in case it is using the binary type handler we were
+ * requested to remove.
+ */
+static void put_binfmt_handler(Node *e)
+{
+	if (refcount_dec_and_test(&e->users)) {
+		if (e->flags & MISC_FMT_OPEN_FILE)
+			filp_close(e->interp_file, NULL);
+		kfree(e);
+	}
+}
+
+/**
+ * load_binfmt_misc - load the binfmt_misc of the caller's user namespace
+ *
+ * To be called in load_misc_binary() to load the relevant struct binfmt_misc.
+ * If a user namespace doesn't have its own binfmt_misc mount it can make use
+ * of its ancestor's binfmt_misc handlers. This mimicks the behavior of
+ * pre-namespaced binfmt_misc where all registered binfmt_misc handlers where
+ * available to all user and user namespaces on the system.
+ *
+ * Return: the binfmt_misc instance of the caller's user namespace
+ */
+static struct binfmt_misc *load_binfmt_misc(void)
+{
+	const struct user_namespace *user_ns;
+	struct binfmt_misc *misc;
+
+	user_ns = current_user_ns();
+	while (user_ns) {
+		/* Pairs with smp_store_release() in bm_fill_super(). */
+		misc = smp_load_acquire(&user_ns->binfmt_misc);
+		if (misc)
+			return misc;
+
+		user_ns = user_ns->parent;
+	}
+
+	return &init_binfmt_misc;
+}
+
+/*
+ * the loader itself
+ */
+static int load_misc_binary(struct linux_binprm *bprm)
+{
+	Node *fmt;
+	struct file *interp_file = NULL;
+	int retval = -ENOEXEC;
+	struct binfmt_misc *misc;
+
+	misc = load_binfmt_misc();
+	if (!misc->enabled)
+		return retval;
+
+	fmt = get_binfmt_handler(misc, bprm);
+	if (!fmt)
+		return retval;
+
+	/* Need to be able to load the file after exec */
+	retval = -ENOENT;
+	if (bprm->interp_flags & BINPRM_FLAGS_PATH_INACCESSIBLE)
+		goto ret;
+
+	if (fmt->flags & MISC_FMT_PRESERVE_ARGV0) {
+		bprm->interp_flags |= BINPRM_FLAGS_PRESERVE_ARGV0;
+	} else {
+		retval = remove_arg_zero(bprm);
+		if (retval)
+			goto ret;
+	}
+
+	if (fmt->flags & MISC_FMT_OPEN_BINARY)
+		bprm->have_execfd = 1;
+
+	/* make argv[1] be the path to the binary */
+	retval = copy_string_kernel(bprm->interp, bprm);
+	if (retval < 0)
+		goto ret;
+	bprm->argc++;
+
+	/* add the interp as argv[0] */
+	retval = copy_string_kernel(fmt->interpreter, bprm);
+	if (retval < 0)
+		goto ret;
+	bprm->argc++;
+
+	/* Update interp in case binfmt_script needs it. */
+	retval = bprm_change_interp(fmt->interpreter, bprm);
+	if (retval < 0)
+		goto ret;
+
+	if (fmt->flags & MISC_FMT_OPEN_FILE) {
+		interp_file = file_clone_open(fmt->interp_file);
+		if (!IS_ERR(interp_file))
+			deny_write_access(interp_file);
+	} else {
+		interp_file = open_exec(fmt->interpreter);
+	}
+	retval = PTR_ERR(interp_file);
+	if (IS_ERR(interp_file))
+		goto ret;
+
+	bprm->interpreter = interp_file;
+	if (fmt->flags & MISC_FMT_CREDENTIALS)
+		bprm->execfd_creds = 1;
+
+	retval = 0;
+ret:
+
+	/*
+	 * If we actually put the node here all concurrent calls to
+	 * load_misc_binary() will have finished. We also know
+	 * that for the refcount to be zero someone must have concurently
+	 * removed the binary type handler from the list and it's our job to
+	 * free it.
+	 */
+	put_binfmt_handler(fmt);
+
+	return retval;
+}
+
+/* Command parsers */
+
+/*
+ * parses and copies one argument enclosed in del from *sp to *dp,
+ * recognising the \x special.
+ * returns pointer to the copied argument or NULL in case of an
+ * error (and sets err) or null argument length.
+ */
+static char *scanarg(char *s, char del)
+{
+	char c;
+
+	while ((c = *s++) != del) {
+		if (c == '\\' && *s == 'x') {
+			s++;
+			if (!isxdigit(*s++))
+				return NULL;
+			if (!isxdigit(*s++))
+				return NULL;
+		}
+	}
+	s[-1] ='\0';
+	return s;
+}
+
+static char *check_special_flags(char *sfs, Node *e)
+{
+	char *p = sfs;
+	int cont = 1;
+
+	/* special flags */
+	while (cont) {
+		switch (*p) {
+		case 'P':
+			pr_debug("register: flag: P (preserve argv0)\n");
+			p++;
+			e->flags |= MISC_FMT_PRESERVE_ARGV0;
+			break;
+		case 'O':
+			pr_debug("register: flag: O (open binary)\n");
+			p++;
+			e->flags |= MISC_FMT_OPEN_BINARY;
+			break;
+		case 'C':
+			pr_debug("register: flag: C (preserve creds)\n");
+			p++;
+			/* this flags also implies the
+			   open-binary flag */
+			e->flags |= (MISC_FMT_CREDENTIALS |
+					MISC_FMT_OPEN_BINARY);
+			break;
+		case 'F':
+			pr_debug("register: flag: F: open interpreter file now\n");
+			p++;
+			e->flags |= MISC_FMT_OPEN_FILE;
+			break;
+		default:
+			cont = 0;
+		}
+	}
+
+	return p;
+}
+
+/*
+ * This registers a new binary format, it recognises the syntax
+ * ':name:type:offset:magic:mask:interpreter:flags'
+ * where the ':' is the IFS, that can be chosen with the first char
+ */
+static Node *create_entry(const char __user *buffer, size_t count)
+{
+	Node *e;
+	int memsize, err;
+	char *buf, *p;
+	char del;
+
+	pr_debug("register: received %zu bytes\n", count);
+
+	/* some sanity checks */
+	err = -EINVAL;
+	if ((count < 11) || (count > MAX_REGISTER_LENGTH))
+		goto out;
+
+	err = -ENOMEM;
+	memsize = sizeof(Node) + count + 8;
+	e = kmalloc(memsize, GFP_KERNEL_ACCOUNT);
+	if (!e)
+		goto out;
+
+	p = buf = (char *)e + sizeof(Node);
+
+	memset(e, 0, sizeof(Node));
+	if (copy_from_user(buf, buffer, count))
+		goto efault;
+
+	del = *p++;	/* delimeter */
+
+	pr_debug("register: delim: %#x {%c}\n", del, del);
+
+	/* Pad the buffer with the delim to simplify parsing below. */
+	memset(buf + count, del, 8);
+
+	/* Parse the 'name' field. */
+	e->name = p;
+	p = strchr(p, del);
+	if (!p)
+		goto einval;
+	*p++ = '\0';
+	if (!e->name[0] ||
+	    !strcmp(e->name, ".") ||
+	    !strcmp(e->name, "..") ||
+	    strchr(e->name, '/'))
+		goto einval;
+
+	pr_debug("register: name: {%s}\n", e->name);
+
+	/* Parse the 'type' field. */
+	switch (*p++) {
+	case 'E':
+		pr_debug("register: type: E (extension)\n");
+		e->flags = 1 << Enabled;
+		break;
+	case 'M':
+		pr_debug("register: type: M (magic)\n");
+		e->flags = (1 << Enabled) | (1 << Magic);
+		break;
+	default:
+		goto einval;
+	}
+	if (*p++ != del)
+		goto einval;
+
+	if (test_bit(Magic, &e->flags)) {
+		/* Handle the 'M' (magic) format. */
+		char *s;
+
+		/* Parse the 'offset' field. */
+		s = strchr(p, del);
+		if (!s)
+			goto einval;
+		*s = '\0';
+		if (p != s) {
+			int r = kstrtoint(p, 10, &e->offset);
+			if (r != 0 || e->offset < 0)
+				goto einval;
+		}
+		p = s;
+		if (*p++)
+			goto einval;
+		pr_debug("register: offset: %#x\n", e->offset);
+
+		/* Parse the 'magic' field. */
+		e->magic = p;
+		p = scanarg(p, del);
+		if (!p)
+			goto einval;
+		if (!e->magic[0])
+			goto einval;
+		if (USE_DEBUG)
+			print_hex_dump_bytes(
+				KBUILD_MODNAME ": register: magic[raw]: ",
+				DUMP_PREFIX_NONE, e->magic, p - e->magic);
+
+		/* Parse the 'mask' field. */
+		e->mask = p;
+		p = scanarg(p, del);
+		if (!p)
+			goto einval;
+		if (!e->mask[0]) {
+			e->mask = NULL;
+			pr_debug("register:  mask[raw]: none\n");
+		} else if (USE_DEBUG)
+			print_hex_dump_bytes(
+				KBUILD_MODNAME ": register:  mask[raw]: ",
+				DUMP_PREFIX_NONE, e->mask, p - e->mask);
+
+		/*
+		 * Decode the magic & mask fields.
+		 * Note: while we might have accepted embedded NUL bytes from
+		 * above, the unescape helpers here will stop at the first one
+		 * it encounters.
+		 */
+		e->size = string_unescape_inplace(e->magic, UNESCAPE_HEX);
+		if (e->mask &&
+		    string_unescape_inplace(e->mask, UNESCAPE_HEX) != e->size)
+			goto einval;
+		if (e->size > BINPRM_BUF_SIZE ||
+		    BINPRM_BUF_SIZE - e->size < e->offset)
+			goto einval;
+		pr_debug("register: magic/mask length: %i\n", e->size);
+		if (USE_DEBUG) {
+			print_hex_dump_bytes(
+				KBUILD_MODNAME ": register: magic[decoded]: ",
+				DUMP_PREFIX_NONE, e->magic, e->size);
+
+			if (e->mask) {
+				int i;
+				char *masked = kmalloc(e->size, GFP_KERNEL_ACCOUNT);
+
+				print_hex_dump_bytes(
+					KBUILD_MODNAME ": register:  mask[decoded]: ",
+					DUMP_PREFIX_NONE, e->mask, e->size);
+
+				if (masked) {
+					for (i = 0; i < e->size; ++i)
+						masked[i] = e->magic[i] & e->mask[i];
+					print_hex_dump_bytes(
+						KBUILD_MODNAME ": register:  magic[masked]: ",
+						DUMP_PREFIX_NONE, masked, e->size);
+
+					kfree(masked);
+				}
+			}
+		}
+	} else {
+		/* Handle the 'E' (extension) format. */
+
+		/* Skip the 'offset' field. */
+		p = strchr(p, del);
+		if (!p)
+			goto einval;
+		*p++ = '\0';
+
+		/* Parse the 'magic' field. */
+		e->magic = p;
+		p = strchr(p, del);
+		if (!p)
+			goto einval;
+		*p++ = '\0';
+		if (!e->magic[0] || strchr(e->magic, '/'))
+			goto einval;
+		pr_debug("register: extension: {%s}\n", e->magic);
+
+		/* Skip the 'mask' field. */
+		p = strchr(p, del);
+		if (!p)
+			goto einval;
+		*p++ = '\0';
+	}
+
+	/* Parse the 'interpreter' field. */
+	e->interpreter = p;
+	p = strchr(p, del);
+	if (!p)
+		goto einval;
+	*p++ = '\0';
+	if (!e->interpreter[0])
+		goto einval;
+	pr_debug("register: interpreter: {%s}\n", e->interpreter);
+
+	/* Parse the 'flags' field. */
+	p = check_special_flags(p, e);
+	if (*p == '\n')
+		p++;
+	if (p != buf + count)
+		goto einval;
+
+	return e;
+
+out:
+	return ERR_PTR(err);
+
+efault:
+	kfree(e);
+	return ERR_PTR(-EFAULT);
+einval:
+	kfree(e);
+	return ERR_PTR(-EINVAL);
+}
+
+/*
+ * Set status of entry/binfmt_misc:
+ * '1' enables, '0' disables and '-1' clears entry/binfmt_misc
+ */
+static int parse_command(const char __user *buffer, size_t count)
+{
+	char s[4];
+
+	if (count > 3)
+		return -EINVAL;
+	if (copy_from_user(s, buffer, count))
+		return -EFAULT;
+	if (!count)
+		return 0;
+	if (s[count - 1] == '\n')
+		count--;
+	if (count == 1 && s[0] == '0')
+		return 1;
+	if (count == 1 && s[0] == '1')
+		return 2;
+	if (count == 2 && s[0] == '-' && s[1] == '1')
+		return 3;
+	return -EINVAL;
+}
+
+/* generic stuff */
+
+static void entry_status(Node *e, char *page)
+{
+	char *dp = page;
+	const char *status = "disabled";
+
+	if (test_bit(Enabled, &e->flags))
+		status = "enabled";
+
+	if (!VERBOSE_STATUS) {
+		sprintf(page, "%s\n", status);
+		return;
+	}
+
+	dp += sprintf(dp, "%s\ninterpreter %s\n", status, e->interpreter);
+
+	/* print the special flags */
+	dp += sprintf(dp, "flags: ");
+	if (e->flags & MISC_FMT_PRESERVE_ARGV0)
+		*dp++ = 'P';
+	if (e->flags & MISC_FMT_OPEN_BINARY)
+		*dp++ = 'O';
+	if (e->flags & MISC_FMT_CREDENTIALS)
+		*dp++ = 'C';
+	if (e->flags & MISC_FMT_OPEN_FILE)
+		*dp++ = 'F';
+	*dp++ = '\n';
+
+	if (!test_bit(Magic, &e->flags)) {
+		sprintf(dp, "extension .%s\n", e->magic);
+	} else {
+		dp += sprintf(dp, "offset %i\nmagic ", e->offset);
+		dp = bin2hex(dp, e->magic, e->size);
+		if (e->mask) {
+			dp += sprintf(dp, "\nmask ");
+			dp = bin2hex(dp, e->mask, e->size);
+		}
+		*dp++ = '\n';
+		*dp = '\0';
+	}
+}
+
+static struct inode *bm_get_inode(struct super_block *sb, int mode)
+{
+	struct inode *inode = new_inode(sb);
+
+	if (inode) {
+		inode->i_ino = get_next_ino();
+		inode->i_mode = mode;
+		simple_inode_init_ts(inode);
+	}
+	return inode;
+}
+
+/**
+ * i_binfmt_misc - retrieve struct binfmt_misc from a binfmt_misc inode
+ * @inode: inode of the relevant binfmt_misc instance
+ *
+ * This helper retrieves struct binfmt_misc from a binfmt_misc inode. This can
+ * be done without any memory barriers because we are guaranteed that
+ * user_ns->binfmt_misc is fully initialized. It was fully initialized when the
+ * binfmt_misc mount was first created.
+ *
+ * Return: struct binfmt_misc of the relevant binfmt_misc instance
+ */
+static struct binfmt_misc *i_binfmt_misc(struct inode *inode)
+{
+	return inode->i_sb->s_user_ns->binfmt_misc;
+}
+
+/**
+ * bm_evict_inode - cleanup data associated with @inode
+ * @inode: inode to which the data is attached
+ *
+ * Cleanup the binary type handler data associated with @inode if a binary type
+ * entry is removed or the filesystem is unmounted and the super block is
+ * shutdown.
+ *
+ * If the ->evict call was not caused by a super block shutdown but by a write
+ * to remove the entry or all entries via bm_{entry,status}_write() the entry
+ * will have already been removed from the list. We keep the list_empty() check
+ * to make that explicit.
+*/
+static void bm_evict_inode(struct inode *inode)
+{
+	Node *e = inode->i_private;
+
+	clear_inode(inode);
+
+	if (e) {
+		struct binfmt_misc *misc;
+
+		misc = i_binfmt_misc(inode);
+		write_lock(&misc->entries_lock);
+		if (!list_empty(&e->list))
+			list_del_init(&e->list);
+		write_unlock(&misc->entries_lock);
+		put_binfmt_handler(e);
+	}
+}
+
+/**
+ * remove_binfmt_handler - remove a binary type handler
+ * @misc: handle to binfmt_misc instance
+ * @e: binary type handler to remove
+ *
+ * Remove a binary type handler from the list of binary type handlers and
+ * remove its associated dentry. This is called from
+ * binfmt_{entry,status}_write(). In the future, we might want to think about
+ * adding a proper ->unlink() method to binfmt_misc instead of forcing caller's
+ * to use writes to files in order to delete binary type handlers. But it has
+ * worked for so long that it's not a pressing issue.
+ */
+static void remove_binfmt_handler(struct binfmt_misc *misc, Node *e)
+{
+	write_lock(&misc->entries_lock);
+	list_del_init(&e->list);
+	write_unlock(&misc->entries_lock);
+	locked_recursive_removal(e->dentry, NULL);
+}
+
+/* /<entry> */
+
+static ssize_t
+bm_entry_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
+{
+	Node *e = file_inode(file)->i_private;
+	ssize_t res;
+	char *page;
+
+	page = kmalloc(PAGE_SIZE, GFP_KERNEL);
+	if (!page)
+		return -ENOMEM;
+
+	entry_status(e, page);
+
+	res = simple_read_from_buffer(buf, nbytes, ppos, page, strlen(page));
+
+	kfree(page);
+	return res;
+}
+
+static ssize_t bm_entry_write(struct file *file, const char __user *buffer,
+				size_t count, loff_t *ppos)
+{
+	struct inode *inode = file_inode(file);
+	Node *e = inode->i_private;
+	int res = parse_command(buffer, count);
+
+	switch (res) {
+	case 1:
+		/* Disable this handler. */
+		clear_bit(Enabled, &e->flags);
+		break;
+	case 2:
+		/* Enable this handler. */
+		set_bit(Enabled, &e->flags);
+		break;
+	case 3:
+		/* Delete this handler. */
+		inode = d_inode(inode->i_sb->s_root);
+		inode_lock_nested(inode, I_MUTEX_PARENT);
+
+		/*
+		 * In order to add new element or remove elements from the list
+		 * via bm_{entry,register,status}_write() inode_lock() on the
+		 * root inode must be held.
+		 * The lock is exclusive ensuring that the list can't be
+		 * modified. Only load_misc_binary() can access but does so
+		 * read-only. So we only need to take the write lock when we
+		 * actually remove the entry from the list.
+		 */
+		if (!list_empty(&e->list))
+			remove_binfmt_handler(i_binfmt_misc(inode), e);
+
+		inode_unlock(inode);
+		break;
+	default:
+		return res;
+	}
+
+	return count;
+}
+
+static const struct file_operations bm_entry_operations = {
+	.read		= bm_entry_read,
+	.write		= bm_entry_write,
+	.llseek		= default_llseek,
+};
+
+/* /register */
+
+/* add to filesystem */
+static int add_entry(Node *e, struct super_block *sb)
+{
+	struct dentry *dentry = simple_start_creating(sb->s_root, e->name);
+	struct inode *inode;
+	struct binfmt_misc *misc;
+
+	if (IS_ERR(dentry))
+		return PTR_ERR(dentry);
+
+	inode = bm_get_inode(sb, S_IFREG | 0644);
+	if (unlikely(!inode)) {
+		simple_done_creating(dentry);
+		return -ENOMEM;
+	}
+
+	refcount_set(&e->users, 1);
+	e->dentry = dentry;
+	inode->i_private = e;
+	inode->i_fop = &bm_entry_operations;
+
+	d_make_persistent(dentry, inode);
+	misc = i_binfmt_misc(inode);
+	write_lock(&misc->entries_lock);
+	list_add(&e->list, &misc->entries);
+	write_unlock(&misc->entries_lock);
+	simple_done_creating(dentry);
+	return 0;
+}
+
+static ssize_t bm_register_write(struct file *file, const char __user *buffer,
+			       size_t count, loff_t *ppos)
+{
+	Node *e;
+	struct super_block *sb = file_inode(file)->i_sb;
+	int err = 0;
+	struct file *f = NULL;
+
+	e = create_entry(buffer, count);
+
+	if (IS_ERR(e))
+		return PTR_ERR(e);
+
+	if (e->flags & MISC_FMT_OPEN_FILE) {
+		/*
+		 * Now that we support unprivileged binfmt_misc mounts make
+		 * sure we use the credentials that the register @file was
+		 * opened with to also open the interpreter. Before that this
+		 * didn't matter much as only a privileged process could open
+		 * the register file.
+		 */
+		scoped_with_creds(file->f_cred)
+			f = open_exec(e->interpreter);
+		if (IS_ERR(f)) {
+			pr_notice("register: failed to install interpreter file %s\n",
+				 e->interpreter);
+			kfree(e);
+			return PTR_ERR(f);
+		}
+		e->interp_file = f;
+	}
+
+	err = add_entry(e, sb);
+	if (err) {
+		if (f) {
+			exe_file_allow_write_access(f);
+			filp_close(f, NULL);
+		}
+		kfree(e);
+		return err;
+	}
+	return count;
+}
+
+static const struct file_operations bm_register_operations = {
+	.write		= bm_register_write,
+	.llseek		= noop_llseek,
+};
+
+/* /status */
+
+static ssize_t
+bm_status_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
+{
+	struct binfmt_misc *misc;
+	char *s;
+
+	misc = i_binfmt_misc(file_inode(file));
+	s = misc->enabled ? "enabled\n" : "disabled\n";
+	return simple_read_from_buffer(buf, nbytes, ppos, s, strlen(s));
+}
+
+static ssize_t bm_status_write(struct file *file, const char __user *buffer,
+		size_t count, loff_t *ppos)
+{
+	struct binfmt_misc *misc;
+	int res = parse_command(buffer, count);
+	Node *e, *next;
+	struct inode *inode;
+
+	misc = i_binfmt_misc(file_inode(file));
+	switch (res) {
+	case 1:
+		/* Disable all handlers. */
+		misc->enabled = false;
+		break;
+	case 2:
+		/* Enable all handlers. */
+		misc->enabled = true;
+		break;
+	case 3:
+		/* Delete all handlers. */
+		inode = d_inode(file_inode(file)->i_sb->s_root);
+		inode_lock_nested(inode, I_MUTEX_PARENT);
+
+		/*
+		 * In order to add new element or remove elements from the list
+		 * via bm_{entry,register,status}_write() inode_lock() on the
+		 * root inode must be held.
+		 * The lock is exclusive ensuring that the list can't be
+		 * modified. Only load_misc_binary() can access but does so
+		 * read-only. So we only need to take the write lock when we
+		 * actually remove the entry from the list.
+		 */
+		list_for_each_entry_safe(e, next, &misc->entries, list)
+			remove_binfmt_handler(misc, e);
+
+		inode_unlock(inode);
+		break;
+	default:
+		return res;
+	}
+
+	return count;
+}
+
+static const struct file_operations bm_status_operations = {
+	.read		= bm_status_read,
+	.write		= bm_status_write,
+	.llseek		= default_llseek,
+};
+
+/* Superblock handling */
+
+static void bm_put_super(struct super_block *sb)
+{
+	struct user_namespace *user_ns = sb->s_fs_info;
+
+	sb->s_fs_info = NULL;
+	put_user_ns(user_ns);
+}
+
+static const struct super_operations s_ops = {
+	.statfs		= simple_statfs,
+	.evict_inode	= bm_evict_inode,
+	.put_super	= bm_put_super,
+};
+
+static int bm_fill_super(struct super_block *sb, struct fs_context *fc)
+{
+	int err;
+	struct user_namespace *user_ns = sb->s_user_ns;
+	struct binfmt_misc *misc;
+	static const struct tree_descr bm_files[] = {
+		[2] = {"status", &bm_status_operations, S_IWUSR|S_IRUGO},
+		[3] = {"register", &bm_register_operations, S_IWUSR},
+		/* last one */ {""}
+	};
+
+	if (WARN_ON(user_ns != current_user_ns()))
+		return -EINVAL;
+
+	/*
+	 * Lazily allocate a new binfmt_misc instance for this namespace, i.e.
+	 * do it here during the first mount of binfmt_misc. We don't need to
+	 * waste memory for every user namespace allocation. It's likely much
+	 * more common to not mount a separate binfmt_misc instance than it is
+	 * to mount one.
+	 *
+	 * While multiple superblocks can exist they are keyed by userns in
+	 * s_fs_info for binfmt_misc. Hence, the vfs guarantees that
+	 * bm_fill_super() is called exactly once whenever a binfmt_misc
+	 * superblock for a userns is created. This in turn lets us conclude
+	 * that when a binfmt_misc superblock is created for the first time for
+	 * a userns there's no one racing us. Therefore we don't need any
+	 * barriers when we dereference binfmt_misc.
+	 */
+	misc = user_ns->binfmt_misc;
+	if (!misc) {
+		/*
+		 * If it turns out that most user namespaces actually want to
+		 * register their own binary type handler and therefore all
+		 * create their own separate binfmt_misc mounts we should
+		 * consider turning this into a kmem cache.
+		 */
+		misc = kzalloc_obj(struct binfmt_misc);
+		if (!misc)
+			return -ENOMEM;
+
+		INIT_LIST_HEAD(&misc->entries);
+		rwlock_init(&misc->entries_lock);
+
+		/* Pairs with smp_load_acquire() in load_binfmt_misc(). */
+		smp_store_release(&user_ns->binfmt_misc, misc);
+	}
+
+	/*
+	 * When the binfmt_misc superblock for this userns is shutdown
+	 * ->enabled might have been set to false and we don't reinitialize
+	 * ->enabled again in put_super() as someone might already be mounting
+	 * binfmt_misc again. It also would be pointless since by the time
+	 * ->put_super() is called we know that the binary type list for this
+	 * bintfmt_misc mount is empty making load_misc_binary() return
+	 * -ENOEXEC independent of whether ->enabled is true. Instead, if
+	 * someone mounts binfmt_misc for the first time or again we simply
+	 * reset ->enabled to true.
+	 */
+	misc->enabled = true;
+
+	err = simple_fill_super(sb, BINFMTFS_MAGIC, bm_files);
+	if (!err)
+		sb->s_op = &s_ops;
+	return err;
+}
+
+static void bm_free(struct fs_context *fc)
+{
+	if (fc->s_fs_info)
+		put_user_ns(fc->s_fs_info);
+}
+
+static int bm_get_tree(struct fs_context *fc)
+{
+	return get_tree_keyed(fc, bm_fill_super, get_user_ns(fc->user_ns));
+}
+
+static const struct fs_context_operations bm_context_ops = {
+	.free		= bm_free,
+	.get_tree	= bm_get_tree,
+};
+
+static int bm_init_fs_context(struct fs_context *fc)
+{
+	fc->ops = &bm_context_ops;
+	return 0;
+}
+
+static struct linux_binfmt misc_format = {
+	.module = THIS_MODULE,
+	.load_binary = load_misc_binary,
+};
+
+static struct file_system_type bm_fs_type = {
+	.owner		= THIS_MODULE,
+	.name		= "binfmt_misc",
+	.init_fs_context = bm_init_fs_context,
+	.fs_flags	= FS_USERNS_MOUNT,
+	.kill_sb	= kill_anon_super,
+};
+MODULE_ALIAS_FS("binfmt_misc");
+
+static int __init init_misc_binfmt(void)
+{
+	int err = register_filesystem(&bm_fs_type);
+	if (!err)
+		insert_binfmt(&misc_format);
+	return err;
+}
+
+static void __exit exit_misc_binfmt(void)
+{
+	unregister_binfmt(&misc_format);
+	unregister_filesystem(&bm_fs_type);
+}
+
+core_initcall(init_misc_binfmt);
+module_exit(exit_misc_binfmt);
+MODULE_DESCRIPTION("Kernel support for miscellaneous binaries");
+MODULE_LICENSE("GPL");