6.5-stable review patch. If anyone has any objections, please let me know.
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From: Bernd Schubert bschubert@ddn.com
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@szeredi.hu CC: stable@vger.kernel.org # 5.15+ Reviewed-by: Christoph Hellwig hch@lst.de Signed-off-by: Bernd Schubert bschubert@ddn.com Reviewed-by: David Sterba dsterba@suse.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- 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);