From: Richard Wareing <rwareing@xxxxxx> This patch has been added to the v4.1 stable tree. If you have any objections, please let us know. =============== [ Upstream commit b31ff3cdf540110da4572e3e29bd172087af65cc ] If using a kernel with CONFIG_XFS_RT=y and we set the RHINHERIT flag on a directory in a filesystem that does not have a realtime device and create a new file in that directory, it gets marked as a real time file. When data is written and a fsync is issued, the filesystem attempts to flush a non-existent rt device during the fsync process. This results in a crash dereferencing a null buftarg pointer in xfs_blkdev_issue_flush(): BUG: unable to handle kernel NULL pointer dereference at 0000000000000008 IP: xfs_blkdev_issue_flush+0xd/0x20 ..... Call Trace: xfs_file_fsync+0x188/0x1c0 vfs_fsync_range+0x3b/0xa0 do_fsync+0x3d/0x70 SyS_fsync+0x10/0x20 do_syscall_64+0x4d/0xb0 entry_SYSCALL64_slow_path+0x25/0x25 Setting RT inode flags does not require special privileges so any unprivileged user can cause this oops to occur. To reproduce, confirm kernel is compiled with CONFIG_XFS_RT=y and run: # mkfs.xfs -f /dev/pmem0 # mount /dev/pmem0 /mnt/test # mkdir /mnt/test/foo # xfs_io -c 'chattr +t' /mnt/test/foo # xfs_io -f -c 'pwrite 0 5m' -c fsync /mnt/test/foo/bar Or just run xfstests with MKFS_OPTIONS="-d rtinherit=1" and wait. Kernels built with CONFIG_XFS_RT=n are not exposed to this bug. Fixes: f538d4da8d52 ("[XFS] write barrier support") Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Richard Wareing <rwareing@xxxxxx> Signed-off-by: Dave Chinner <david@xxxxxxxxxxxxx> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxx> --- fs/xfs/xfs_linux.h | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/fs/xfs/xfs_linux.h b/fs/xfs/xfs_linux.h index 7c7842c85a08..530c2f9c47c7 100644 --- a/fs/xfs/xfs_linux.h +++ b/fs/xfs/xfs_linux.h @@ -376,7 +376,14 @@ static inline __uint64_t howmany_64(__uint64_t x, __uint32_t y) #endif /* DEBUG */ #ifdef CONFIG_XFS_RT -#define XFS_IS_REALTIME_INODE(ip) ((ip)->i_d.di_flags & XFS_DIFLAG_REALTIME) + +/* + * make sure we ignore the inode flag if the filesystem doesn't have a + * configured realtime device. + */ +#define XFS_IS_REALTIME_INODE(ip) \ + (((ip)->i_d.di_flags & XFS_DIFLAG_REALTIME) && \ + (ip)->i_mount->m_rtdev_targp) #else #define XFS_IS_REALTIME_INODE(ip) (0) #endif -- 2.11.0