[Bug 200925] New: null pointer dereference in xfs_dir_isempty()

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https://bugzilla.kernel.org/show_bug.cgi?id=200925

            Bug ID: 200925
           Summary: null pointer dereference in xfs_dir_isempty()
           Product: File System
           Version: 2.5
    Kernel Version: 4.18
          Hardware: All
                OS: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: XFS
          Assignee: filesystem_xfs@xxxxxxxxxxxxxxxxxxxxxx
          Reporter: wen.xu@xxxxxxxxxx
        Regression: No

Created attachment 278069
  --> https://bugzilla.kernel.org/attachment.cgi?id=278069&action=edit
poc.c

- Reproduce
# mkdir mnt
# mount -t xfs 79.img mnt
# gcc 79.c
# ./a.out ./mnt

- Kernel message
Check attachment: 79.log

- Reason
https://elixir.bootlin.com/linux/latest/source/fs/xfs/libxfs/xfs_dir2.c#L185
        sfp = (xfs_dir2_sf_hdr_t *)dp->i_df.if_u1.if_data;
        return !sfp->count;
Missing checks on sfp.

Reported by Wen Xu (wen.xu@xxxxxxxxxx) from SSLab.

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