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    Subject[PATCH 3.2 63/74] xfs: XFS_IS_REALTIME_INODE() should be false if no rt device present
    3.2.94-rc1 review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Richard Wareing <rwareing@fb.com>

    commit b31ff3cdf540110da4572e3e29bd172087af65cc upstream.

    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")
    Signed-off-by: Richard Wareing <rwareing@fb.com>
    Signed-off-by: Dave Chinner <david@fromorbit.com>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    [bwh: Backported to 3.2: adjust filename]
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    fs/xfs/xfs_dinode.h | 9 ++++++++-
    1 file changed, 8 insertions(+), 1 deletion(-)

    --- a/fs/xfs/xfs_dinode.h
    +++ b/fs/xfs/xfs_dinode.h
    @@ -201,7 +201,14 @@ static inline void xfs_dinode_put_rdev(s
    #define XFS_DIFLAG_FILESTREAM (1 << XFS_DIFLAG_FILESTREAM_BIT)

    #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
    \
     
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