This is a note to let you know that I've just added the patch titled
btrfs: file_remove_privs needs an exclusive lock in direct io write
to the 6.5-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
btrfs-file_remove_privs-needs-an-exclusive-lock-in-direct-io-write.patch
and it can be found in the queue-6.5 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 9af86694fd5d387992699ec99007ed374966ce9a Mon Sep 17 00:00:00 2001
From: Bernd Schubert <bschubert@xxxxxxx>
Date: Wed, 6 Sep 2023 17:59:03 +0200
Subject: btrfs: file_remove_privs needs an exclusive lock in direct io write
From: Bernd Schubert <bschubert@xxxxxxx>
commit 9af86694fd5d387992699ec99007ed374966ce9a upstream.
This was noticed by Miklos that file_remove_privs might call into
notify_change(), which requires to hold an exclusive lock. The problem
exists in FUSE and btrfs. We can fix it without any additional helpers
from VFS, in case the privileges would need to be dropped, change the
lock type to be exclusive and redo the loop.
Fixes: e9adabb9712e ("btrfs: use shared lock for direct writes within EOF")
CC: Miklos Szeredi <miklos@xxxxxxxxxx>
CC: stable@xxxxxxxxxxxxxxx # 5.15+
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Signed-off-by: Bernd Schubert <bschubert@xxxxxxx>
Reviewed-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/btrfs/file.c | 16 ++++++++++++++--
1 file changed, 14 insertions(+), 2 deletions(-)
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1466,8 +1466,13 @@ static ssize_t btrfs_direct_write(struct
if (iocb->ki_flags & IOCB_NOWAIT)
ilock_flags |= BTRFS_ILOCK_TRY;
- /* If the write DIO is within EOF, use a shared lock */
- if (iocb->ki_pos + iov_iter_count(from) <= i_size_read(inode))
+ /*
+ * If the write DIO is within EOF, use a shared lock and also only if
+ * security bits will likely not be dropped by file_remove_privs() called
+ * from btrfs_write_check(). Either will need to be rechecked after the
+ * lock was acquired.
+ */
+ if (iocb->ki_pos + iov_iter_count(from) <= i_size_read(inode) && IS_NOSEC(inode))
ilock_flags |= BTRFS_ILOCK_SHARED;
relock:
@@ -1475,6 +1480,13 @@ relock:
if (err < 0)
return err;
+ /* Shared lock cannot be used with security bits set. */
+ if ((ilock_flags & BTRFS_ILOCK_SHARED) && !IS_NOSEC(inode)) {
+ btrfs_inode_unlock(BTRFS_I(inode), ilock_flags);
+ ilock_flags &= ~BTRFS_ILOCK_SHARED;
+ goto relock;
+ }
+
err = generic_write_checks(iocb, from);
if (err <= 0) {
btrfs_inode_unlock(BTRFS_I(inode), ilock_flags);
Patches currently in stable-queue which might be from bschubert@xxxxxxx are
queue-6.5/btrfs-file_remove_privs-needs-an-exclusive-lock-in-direct-io-write.patch
