xfs: sanity check directory inode di_size

commit 3c6f46eacd876bd723a9bad3c6882714c052fd8e upstream.

This changes fixes an assertion hit when fuzzing on-disk
i_mode values.

The easy case to fix is when changing an empty file
i_mode to S_IFDIR. In this case, xfs_dinode_verify()
detects an illegal zero size for directory and fails
to load the inode structure from disk.

For the case of non empty file whose i_mode is changed
to S_IFDIR, the ASSERT() statement in xfs_dir2_isblock()
is replaced with return -EFSCORRUPTED, to avoid interacting
with corrupted jusk also when XFS_DEBUG is disabled.

Suggested-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

2 files changed, 7 insertions, 3 deletions

diff --git a/fs/xfs/libxfs/xfs_dir2.c b/fs/xfs/libxfs/xfs_dir2.c
index 20a96dd5af7e..ec326d272efb 100644
--- a/fs/xfs/libxfs/xfs_dir2.c
+++ b/fs/xfs/libxfs/xfs_dir2.c
@@ -631,7 +631,8 @@ xfs_dir2_isblock(
         if ((rval = xfs_bmap_last_offset(args->dp, &last, XFS_DATA_FORK)))
                 return rval;
         rval = XFS_FSB_TO_B(args->dp->i_mount, last) == args->geo->blksize;
-        ASSERT(rval == 0 || args->dp->i_d.di_size == args->geo->blksize);
+        if (rval != 0 && args->dp->i_d.di_size != args->geo->blksize)
+                return -EFSCORRUPTED;
         *vp = rval;
         return 0;
 }
diff --git a/fs/xfs/libxfs/xfs_inode_buf.c b/fs/xfs/libxfs/xfs_inode_buf.c
index c906e50515f0..977245de8953 100644
--- a/fs/xfs/libxfs/xfs_inode_buf.c
+++ b/fs/xfs/libxfs/xfs_inode_buf.c
@@ -386,6 +386,7 @@ xfs_dinode_verify(
         struct xfs_inode        *ip,
         struct xfs_dinode       *dip)
 {
+        uint16_t                mode;
         uint16_t                flags;
         uint64_t                flags2;
 
@@ -396,8 +397,10 @@ xfs_dinode_verify(
         if (be64_to_cpu(dip->di_size) & (1ULL << 63))
                 return false;
 
-        /* No zero-length symlinks. */
-        if (S_ISLNK(be16_to_cpu(dip->di_mode)) && dip->di_size == 0)
+        mode = be16_to_cpu(dip->di_mode);
+
+        /* No zero-length symlinks/dirs. */
+        if ((S_ISLNK(mode) || S_ISDIR(mode)) && dip->di_size == 0)
                 return false;
 
         /* only version 3 or greater inodes are extensively verified here */