netfs: zero the tail of a short DIO/unbuffered readgrafted

The buffered read collector zero-fills the tail of a short read that
stops below the inode's i_size (netfs_clear_unread()), so a read that
races an extending write still returns the expected number of bytes.
The non-buffered collector path does no such thing: it just records
how much was transferred.

Add the same zero-fill for the non-buffered case, gated on
NETFS_SREQ_CLEAR_TAIL: a subreq's source sets that flag when a short
result from it is known to be safe to treat as a hole, as opposed to
NETFS_SREQ_HIT_EOF, which means the read genuinely ran off the end of
the file and should be reported short as-is. Only CLEAR_TAIL should
zero-fill here; a real EOF must stay a real short read.

No source currently sets CLEAR_TAIL on an unbuffered/DIO subrequest,
so this is inert on its own -- a following change teaches cifs to set
it in the one case that needs it.

Fixes: e2d46f2ec332 ("netfs: Change the read result collector to only use one work item")
Reviewed-by: David Howells <dhowells@redhat.com>
Reviewed-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Paulo Alcantara <pc@manguebit.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Ronnie Sahlberg <ronniesahlberg@gmail.com>
Cc: Shyam Prasad N <sprasad@microsoft.com>
Cc: Tom Talpey <tom@talpey.com>
Cc: Bharath SM <bharathsm@microsoft.com>
Cc: stable@vger.kernel.org

1 files changed, 251 insertions, 0 deletions

diff --git a/drivers/tty/tty_audit.c b/drivers/tty/tty_audit.c
new file mode 100644
index 000000000..d014af6ab
--- /dev/null
+++ b/drivers/tty/tty_audit.c
@@ -0,0 +1,251 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Creating audit events from TTY input.
+ *
+ * Copyright (C) 2007 Red Hat, Inc.  All rights reserved.
+ *
+ * Authors: Miloslav Trmac <mitr@redhat.com>
+ */
+
+#include <linux/audit.h>
+#include <linux/slab.h>
+#include <linux/tty.h>
+#include "tty.h"
+
+#define TTY_AUDIT_BUF_SIZE	4096
+
+struct tty_audit_buf {
+	struct mutex mutex;	/* Protects all data below */
+	dev_t dev;		/* The TTY which the data is from */
+	bool icanon;
+	size_t valid;
+	u8 *data;		/* Allocated size TTY_AUDIT_BUF_SIZE */
+};
+
+static struct tty_audit_buf *tty_audit_buf_ref(void)
+{
+	struct tty_audit_buf *buf;
+
+	buf = current->signal->tty_audit_buf;
+	WARN_ON(buf == ERR_PTR(-ESRCH));
+	return buf;
+}
+
+static struct tty_audit_buf *tty_audit_buf_alloc(void)
+{
+	struct tty_audit_buf *buf;
+
+	buf = kzalloc_obj(*buf);
+	if (!buf)
+		goto err;
+
+	buf->data = kmalloc(TTY_AUDIT_BUF_SIZE, GFP_KERNEL);
+	if (!buf->data)
+		goto err_buf;
+
+	mutex_init(&buf->mutex);
+
+	return buf;
+
+err_buf:
+	kfree(buf);
+err:
+	return NULL;
+}
+
+static void tty_audit_buf_free(struct tty_audit_buf *buf)
+{
+	WARN_ON(buf->valid != 0);
+	kfree(buf->data);
+	kfree(buf);
+}
+
+static void tty_audit_log(const char *description, dev_t dev,
+			  const u8 *data, size_t size)
+{
+	struct audit_buffer *ab;
+	pid_t pid = task_pid_nr(current);
+	uid_t uid = from_kuid(&init_user_ns, task_uid(current));
+	uid_t loginuid = from_kuid(&init_user_ns, audit_get_loginuid(current));
+	unsigned int sessionid = audit_get_sessionid(current);
+	char name[TASK_COMM_LEN];
+
+	ab = audit_log_start(audit_context(), GFP_KERNEL, AUDIT_TTY);
+	if (!ab)
+		return;
+
+	audit_log_format(ab, "%s pid=%u uid=%u auid=%u ses=%u major=%d minor=%d comm=",
+			 description, pid, uid, loginuid, sessionid,
+			 MAJOR(dev), MINOR(dev));
+	get_task_comm(name, current);
+	audit_log_untrustedstring(ab, name);
+	audit_log_format(ab, " data=");
+	audit_log_n_hex(ab, data, size);
+	audit_log_end(ab);
+}
+
+/*
+ *	tty_audit_buf_push	-	Push buffered data out
+ *
+ *	Generate an audit message from the contents of @buf, which is owned by
+ *	the current task.  @buf->mutex must be locked.
+ */
+static void tty_audit_buf_push(struct tty_audit_buf *buf)
+{
+	if (buf->valid == 0)
+		return;
+	if (audit_enabled == AUDIT_OFF) {
+		buf->valid = 0;
+		return;
+	}
+	tty_audit_log("tty", buf->dev, buf->data, buf->valid);
+	buf->valid = 0;
+}
+
+/**
+ *	tty_audit_exit	-	Handle a task exit
+ *
+ *	Make sure all buffered data is written out and deallocate the buffer.
+ *	Only needs to be called if current->signal->tty_audit_buf != %NULL.
+ *
+ *	The process is single-threaded at this point; no other threads share
+ *	current->signal.
+ */
+void tty_audit_exit(void)
+{
+	struct tty_audit_buf *buf;
+
+	buf = xchg(&current->signal->tty_audit_buf, ERR_PTR(-ESRCH));
+	if (!buf)
+		return;
+
+	tty_audit_buf_push(buf);
+	tty_audit_buf_free(buf);
+}
+
+/*
+ *	tty_audit_fork	-	Copy TTY audit state for a new task
+ *
+ *	Set up TTY audit state in @sig from current.  @sig needs no locking.
+ */
+void tty_audit_fork(struct signal_struct *sig)
+{
+	sig->audit_tty = current->signal->audit_tty;
+}
+
+/*
+ *	tty_audit_tiocsti	-	Log TIOCSTI
+ */
+void tty_audit_tiocsti(const struct tty_struct *tty, u8 ch)
+{
+	dev_t dev;
+
+	dev = MKDEV(tty->driver->major, tty->driver->minor_start) + tty->index;
+	if (tty_audit_push())
+		return;
+
+	if (audit_enabled)
+		tty_audit_log("ioctl=TIOCSTI", dev, &ch, 1);
+}
+
+/*
+ *	tty_audit_push	-	Flush current's pending audit data
+ *
+ *	Returns 0 if success, -EPERM if tty audit is disabled
+ */
+int tty_audit_push(void)
+{
+	struct tty_audit_buf *buf;
+
+	if (~current->signal->audit_tty & AUDIT_TTY_ENABLE)
+		return -EPERM;
+
+	buf = tty_audit_buf_ref();
+	if (!IS_ERR_OR_NULL(buf)) {
+		mutex_lock(&buf->mutex);
+		tty_audit_buf_push(buf);
+		mutex_unlock(&buf->mutex);
+	}
+	return 0;
+}
+
+/*
+ *	tty_audit_buf_get	-	Get an audit buffer.
+ *
+ *	Get an audit buffer, allocate it if necessary.  Return %NULL
+ *	if out of memory or ERR_PTR(-ESRCH) if tty_audit_exit() has already
+ *	occurred.  Otherwise, return a new reference to the buffer.
+ */
+static struct tty_audit_buf *tty_audit_buf_get(void)
+{
+	struct tty_audit_buf *buf;
+
+	buf = tty_audit_buf_ref();
+	if (buf)
+		return buf;
+
+	buf = tty_audit_buf_alloc();
+	if (buf == NULL) {
+		audit_log_lost("out of memory in TTY auditing");
+		return NULL;
+	}
+
+	/* Race to use this buffer, free it if another wins */
+	if (cmpxchg(&current->signal->tty_audit_buf, NULL, buf) != NULL)
+		tty_audit_buf_free(buf);
+	return tty_audit_buf_ref();
+}
+
+/*
+ *	tty_audit_add_data	-	Add data for TTY auditing.
+ *
+ *	Audit @data of @size from @tty, if necessary.
+ */
+void tty_audit_add_data(const struct tty_struct *tty, const void *data,
+			size_t size)
+{
+	struct tty_audit_buf *buf;
+	unsigned int audit_tty;
+	bool icanon = L_ICANON(tty);
+	dev_t dev;
+
+	audit_tty = READ_ONCE(current->signal->audit_tty);
+	if (~audit_tty & AUDIT_TTY_ENABLE)
+		return;
+
+	if (unlikely(size == 0))
+		return;
+
+	if (tty->driver->type == TTY_DRIVER_TYPE_PTY
+	    && tty->driver->subtype == PTY_TYPE_MASTER)
+		return;
+
+	if ((~audit_tty & AUDIT_TTY_LOG_PASSWD) && icanon && !L_ECHO(tty))
+		return;
+
+	buf = tty_audit_buf_get();
+	if (IS_ERR_OR_NULL(buf))
+		return;
+
+	mutex_lock(&buf->mutex);
+	dev = MKDEV(tty->driver->major, tty->driver->minor_start) + tty->index;
+	if (buf->dev != dev || buf->icanon != icanon) {
+		tty_audit_buf_push(buf);
+		buf->dev = dev;
+		buf->icanon = icanon;
+	}
+	do {
+		size_t run;
+
+		run = TTY_AUDIT_BUF_SIZE - buf->valid;
+		if (run > size)
+			run = size;
+		memcpy(buf->data + buf->valid, data, run);
+		buf->valid += run;
+		data += run;
+		size -= run;
+		if (buf->valid == TTY_AUDIT_BUF_SIZE)
+			tty_audit_buf_push(buf);
+	} while (size != 0);
+	mutex_unlock(&buf->mutex);
+}