• Richard Wareing's avatar
    xfs: XFS_IS_REALTIME_INODE() should be false if no rt device present · 5b82e0e9
    Richard Wareing authored
    commit b31ff3cd 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: f538d4da ("[XFS] write barrier support")
    Signed-off-by: default avatarRichard Wareing <rwareing@fb.com>
    Signed-off-by: default avatarDave Chinner <david@fromorbit.com>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    5b82e0e9
xfs_linux.h 9.22 KB