xfs: sanity check attr fork size

Recently we have quite a few kerneloops reports about dereferencing a NULL
if_data in the attribute fork.  From looking over the code this can only
happen if we pass a 0 size argument to xfs_iformat_local.  This implies some
sort of corruption and in fact the only mailinglist report about this from
earlier this year was after a powerfail presumably on a system with write
cache and without barriers.

Add a quick sanity check for the attr fork size in xfs_iformat to catch
these early and without an oops.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <david@fromorbit.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
index be2ca4d67b53..e7ae08d1df48 100644
--- a/fs/xfs/xfs_inode.c
+++ b/fs/xfs/xfs_inode.c
@@ -424,6 +424,19 @@ xfs_iformat(
         case XFS_DINODE_FMT_LOCAL:
                 atp = (xfs_attr_shortform_t *)XFS_DFORK_APTR(dip);
                 size = be16_to_cpu(atp->hdr.totsize);
+
+                if (unlikely(size < sizeof(struct xfs_attr_sf_hdr))) {
+                        xfs_fs_repair_cmn_err(CE_WARN, ip->i_mount,
+                                "corrupt inode %Lu "
+                                "(bad attr fork size %Ld).",
+                                (unsigned long long) ip->i_ino,
+                                (long long) size);
+                        XFS_CORRUPTION_ERROR("xfs_iformat(8)",
+                                             XFS_ERRLEVEL_LOW,
+                                             ip->i_mount, dip);
+                        return XFS_ERROR(EFSCORRUPTED);
+                }
+
                 error = xfs_iformat_local(ip, dip, XFS_ATTR_FORK, size);
                 break;
         case XFS_DINODE_FMT_EXTENTS: