ext4: add sanity checking to count_overhead()

[ Upstream commit c48ae41bafe31e9a66d8be2ced4e42a6b57fa814 ]

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>
Cc: stable@vger.kernel.org
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index ea08ab7173b53100d978819161ef3ee7ebb5766a..a5200023e6045e550fa20cbeafc01a7bc138a460 100644 (file)
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -3325,10 +3325,15 @@ 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;