ext4: limit entries returned when counting fsmap records

If userspace asked fsmap to try to count the number of entries, we cannot
return more than UINT_MAX entries because fmh_entries is u32.
Therefore, stop counting if we hit this limit or else we will waste time
to return truncated results.

Fixes: 0c9ec4beecac ("ext4: support GETFSMAP ioctls")
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Link: https://lore.kernel.org/r/20201001222148.GA49520@magnolia
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/fs/ext4/fsmap.c b/fs/ext4/fsmap.c
index 005c0ae..b232c27 100644 (file)
--- a/fs/ext4/fsmap.c
+++ b/fs/ext4/fsmap.c
@@ -108,6 +108,9 @@ static int ext4_getfsmap_helper(struct super_block *sb,
 
        /* Are we just counting mappings? */
        if (info->gfi_head->fmh_count == 0) {
+               if (info->gfi_head->fmh_entries == UINT_MAX)
+                       return EXT4_QUERY_RANGE_ABORT;
+
                if (rec_fsblk > info->gfi_next_fsblk)
                        info->gfi_head->fmh_entries++;