ext4: add sanity checking to count_overhead()

commit c48ae41bafe31e9a66d8be2ced4e42a6b57fa814 upstream.

The commit "ext4: sanity check the block and cluster size at mount
time" should prevent any problems, but in case the superblock is
modified while the file system is mounted, add an extra safety check
to make sure we won't overrun the allocated buffer.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 6c67a988bfcee5787820a72681dda836269b7501..6362896f58756eb25c8ffe97105d32ff3b0d8cb1 100644 (file)
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -3257,10 +3257,15 @@ static int count_overhead(struct super_block *sb, ext4_group_t grp,
                        ext4_set_bit(s++, buf);
                        count++;
                }
-               for (j = ext4_bg_num_gdb(sb, grp); j > 0; j--) {
-                       ext4_set_bit(EXT4_B2C(sbi, s++), buf);
-                       count++;
+               j = ext4_bg_num_gdb(sb, grp);
+               if (s + j > EXT4_BLOCKS_PER_GROUP(sb)) {
+                       ext4_error(sb, "Invalid number of block group "
+                                  "descriptor blocks: %d", j);
+                       j = EXT4_BLOCKS_PER_GROUP(sb) - s;
                }
+               count += j;
+               for (; j > 0; j--)
+                       ext4_set_bit(EXT4_B2C(sbi, s++), buf);
        }
        if (!count)
                return 0;