From 034dd340b08be1f2f0477ad16131d609f9dbd53c Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Sun, 30 Aug 2026 09:22:00 -0700 Subject: Merge tag 'trace-v7.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace Pull tracing fixes from Steven Rostedt: - Fix error output of boot instance creation failure Currently if a boot instance creation fails, instead of printing out the name of the instance that failed, it prints "(null)". That is because it prints "cur_str" that had already been processed by strsep(). Print the saved name instead. While at it, print the error code of the failure. - Fix use-after-free for same named historgrams Histograms can be named so that they can be used in multiple events. But if the named histogram has a variable attached, the second event that uses the named histogram which duplicates it and needs to free the original after duplication leaves the old variable in place and still visible. If another histogram uses than variable, it will use the stale one which will try to reference the freed duplicate histogram and crash the kernel. Free the duplicate variables along with the duplicated histogram data. - Check return value of kthread_run() in event self test The events self tests uses a kthread for testing but does not check if it succeeded in creating a kthread. If the kthread creation were to fail, the code will still try to call kthread_stop() on the error returned. - Fix race between reading trace_pipe and updating subbuffer size If a user is reading the trace_pipe file at the same time they update the ring buffer sub-buffer size, can cause the trace_pipe read to read stale data. Add trace_access_lock() around updating the ring buffer sub-buffer size. - Fix eventfs_inode on failure path in creation of the events directory In the creation of the "events" directory, if after allocating the eventfs_inode a failure is detected, it calls cleanup_ei() which calls free_ei(). The free_ei() will test if eventfs_inode being freed has no children. It is a bug if it does. But on the failure case of the creation of the "events" directory, the children lists have not yet been initialized and the free will trigger a warning because list_empty() on an uninitialized list returns false. Move the initialization into init_ei() where it makes more sense and makes sure that a created eventfs_inode has its lists initialized upon creation. - Check return value of kthread_run() in ftrace direct sample code The sample code that shows how to use the ftrace direct calls does not test the return of kthread_run() to see if it succeeds. Return a failure if the kthread_run() doesn't succeed. - Clear user events state on fork in case of alloc failure On fork, the child gets a pointer to the parent's user events state. It makes a copy of it then updates the child's pointer to it. But if the allocation fails, the duplication function leaves the child with a pointer to its parent's descriptor. When the child cleans up its data, it will free the parent's descriptor while the parent is still using it. In the duplication function, set the child's user_event_mm to NULL before testing if the allocation succeeded, and when it exits it will not free the parent's descriptor. - Fix retry exhaustion in simple ring buffer reader swap simple_ring_buffer_swap_reader_page() starts with retry set to 8 and post-decrements it only after a failed link replacement. On the final attempt, a successful replacement leaves retry at zero, while a failed replacement leaves it at -1. But the check for success expects the retry value to be non-zero and exits with an error on zero. This is the opposite result. Fix it. - Fail nicely when the remote swap_reader_page() returns an error Currently, if the swap_reader_page() of a remote buffer fails, it triggers a WARN_ON_ONCE() and continues normally. Instead, have it exit with an error and a pr_warn() print instead of a full WARNING. * tag 'trace-v7.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace: ring-buffer: Stop remote reader update when page swap fails tracing: Fix retry exhaustion in simple ring buffer reader swap tracing/user_events: Clear copied tracing state before fork duplication samples/ftrace: Fix kthread_stop() on ERR_PTR in ftrace-direct-multi-modify samples/ftrace: Fix kthread_stop() on ERR_PTR in ftrace-direct-modify eventfs: Initialize ei->children and ei->list in init_ei() tracing: Fix use-after-free in trace_pipe read on sub-buffer order change tracing: Fix crash passing ERR_PTR to kthread_stop() tracing: Fix use-after-free with same-name named triggers tracing: Fix logged instance name on creation failure --- fs/fs_struct.c | 252 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 252 insertions(+) create mode 100644 fs/fs_struct.c (limited to 'fs/fs_struct.c') diff --git a/fs/fs_struct.c b/fs/fs_struct.c new file mode 100644 index 000000000..34699f3b6 --- /dev/null +++ b/fs/fs_struct.c @@ -0,0 +1,252 @@ +// SPDX-License-Identifier: GPL-2.0-only +#include +#include +#include +#include +#include +#include +#include +#include +#include "internal.h" +#include "mount.h" + +/* + * Replace the fs->{rootmnt,root} with {mnt,dentry}. Put the old values. + * It can block. + */ +void set_fs_root(struct fs_struct *fs, const struct path *path) +{ + struct path old_root; + + path_get(path); + write_seqlock(&fs->seq); + old_root = fs->root; + fs->root = *path; + write_sequnlock(&fs->seq); + if (old_root.dentry) + path_put(&old_root); +} + +/* + * Replace the fs->{pwdmnt,pwd} with {mnt,dentry}. Put the old values. + * It can block. + */ +void set_fs_pwd(struct fs_struct *fs, const struct path *path) +{ + struct path old_pwd; + + path_get(path); + write_seqlock(&fs->seq); + old_pwd = fs->pwd; + fs->pwd = *path; + write_sequnlock(&fs->seq); + + if (old_pwd.dentry) + path_put(&old_pwd); +} + +static inline int replace_path(struct path *p, const struct path *old, const struct path *new) +{ + if (likely(p->dentry != old->dentry || p->mnt != old->mnt)) + return 0; + *p = *new; + return 1; +} + +void chroot_fs_refs(const struct path *old_root, const struct path *new_root) +{ + struct task_struct *g, *p; + struct fs_struct *fs; + int count = 0; + + read_lock(&tasklist_lock); + for_each_process_thread(g, p) { + if (p->flags & (PF_KTHREAD | PF_EXITING | PF_DUMPCORE)) + continue; + + task_lock(p); + fs = p->real_fs; + if (fs) { + int hits = 0; + write_seqlock(&fs->seq); + hits += replace_path(&fs->root, old_root, new_root); + hits += replace_path(&fs->pwd, old_root, new_root); + while (hits--) { + count++; + path_get(new_root); + } + write_sequnlock(&fs->seq); + } + task_unlock(p); + } + read_unlock(&tasklist_lock); + while (count--) + path_put(old_root); +} + +void free_fs_struct(struct fs_struct *fs) +{ + path_put(&fs->root); + path_put(&fs->pwd); + kmem_cache_free(fs_cachep, fs); +} + +void exit_fs(struct task_struct *tsk) +{ + struct fs_struct *fs = tsk->real_fs; + + if (fs) { + int kill; + task_lock(tsk); + read_seqlock_excl(&fs->seq); + tsk->real_fs = NULL; + tsk->fs = NULL; + kill = !--fs->users; + read_sequnlock_excl(&fs->seq); + task_unlock(tsk); + if (kill) + free_fs_struct(fs); + } +} + +struct fs_struct *copy_fs_struct(struct fs_struct *old) +{ + struct fs_struct *fs = kmem_cache_alloc(fs_cachep, GFP_KERNEL); + /* We don't need to lock fs - think why ;-) */ + if (fs) { + fs->users = 1; + fs->in_exec = 0; + seqlock_init(&fs->seq); + fs->umask = old->umask; + + read_seqlock_excl(&old->seq); + fs->root = old->root; + path_get(&fs->root); + fs->pwd = old->pwd; + path_get(&fs->pwd); + read_sequnlock_excl(&old->seq); + } + return fs; +} + +int unshare_fs_struct(void) +{ + struct fs_struct *fs = current->real_fs; + struct fs_struct *new_fs = copy_fs_struct(fs); + int kill; + + if (!new_fs) + return -ENOMEM; + + task_lock(current); + read_seqlock_excl(&fs->seq); + VFS_WARN_ON_ONCE(fs != current->fs); + kill = !--fs->users; + current->fs = new_fs; + current->real_fs = new_fs; + read_sequnlock_excl(&fs->seq); + task_unlock(current); + + if (kill) + free_fs_struct(fs); + + return 0; +} +EXPORT_SYMBOL_GPL(unshare_fs_struct); + +/* + * PID 1 may choose to stop sharing fs_struct state with us. + * Either via unshare(CLONE_FS) or unshare(CLONE_NEWNS). Of + * course, PID 1 could have chosen to create arbitrary process + * trees that all share fs_struct state via CLONE_FS. This is a + * strong statement: We only care about PID 1 aka the thread-group + * leader so subthread's fs_struct state doesn't matter. + * + * PID 1 unsharing fs_struct state is a bug. PID 1 relies on + * various kthreads to be able to perform work based on its + * fs_struct state. Breaking that contract sucks for both sides. + * So just don't bother with extra work for this. No sane init + * system should ever do this. + * + * On older kernels if PID 1 unshared its filesystem state with us the + * kernel simply used the stale fs_struct state implicitly pinning + * anything that PID 1 had last used. Even if PID 1 might've moved on to + * some completely different fs_struct state and might've even unmounted + * the old root. + * + * This has hilarious consequences: Think continuing to dump coredump + * state into an implicitly pinned directory somewhere. Calling random + * binaries in the old rootfs via usermodehelpers. + * + * Be aggressive about this: We simply reject operating on stale + * fs_struct state by reverting to nullfs. Every kworker that does + * lookups after this point will fail. Every usermodehelper call will + * fail. Tough luck but let's be kind and emit a warning to userspace. + */ +static inline void validate_fs_switch(struct fs_struct *old_fs) +{ + might_sleep(); + + if (likely(current->pid != 1)) + return; + /* @old_fs may be dangling but for comparison it's fine */ + if (old_fs != userspace_init_fs) + return; + pr_warn("VFS: Pid 1 stopped sharing filesystem state\n"); + set_fs_root(userspace_init_fs, &init_fs.root); + set_fs_pwd(userspace_init_fs, &init_fs.root); +} + +struct fs_struct *switch_fs_struct(struct fs_struct *new_fs) +{ + struct fs_struct *fs; + + scoped_guard(task_lock, current) { + fs = current->fs; + VFS_WARN_ON_ONCE(fs != current->real_fs); + read_seqlock_excl(&fs->seq); + current->fs = new_fs; + current->real_fs = new_fs; + if (--fs->users) + new_fs = NULL; + else + new_fs = fs; + read_sequnlock_excl(&fs->seq); + } + + validate_fs_switch(fs); + return new_fs; +} + +/* to be mentioned only in INIT_TASK */ +struct fs_struct init_fs = { + .users = 1, + .seq = __SEQLOCK_UNLOCKED(init_fs.seq), + .umask = 0022, +}; + +struct fs_struct *userspace_init_fs __ro_after_init; +EXPORT_SYMBOL_GPL(userspace_init_fs); + +void __init init_userspace_fs(void) +{ + struct mount *m; + struct path root; + + /* Move PID 1 from nullfs into the initramfs. */ + m = topmost_overmount(current->nsproxy->mnt_ns->root); + root.mnt = &m->mnt; + root.dentry = root.mnt->mnt_root; + + VFS_WARN_ON_ONCE(current->pid != 1); + + set_fs_root(current->fs, &root); + set_fs_pwd(current->fs, &root); + + /* Hold a reference for the global pointer. */ + read_seqlock_excl(¤t->fs->seq); + current->fs->users++; + read_sequnlock_excl(¤t->fs->seq); + + userspace_init_fs = current->fs; +} -- cgit v1.3.1