linux-kernel - [PATCH 4.9 43/83] ext4: add sanity checking to count

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Date:   Wed,  4 Jan 2017 21:06:35 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Theodore Tso <tytso@....edu>
Subject: [PATCH 4.9 43/83] ext4: add sanity checking to count_overhead()

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Theodore Ts'o <tytso@....edu>

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@....edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/ext4/super.c |   11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -3193,10 +3193,15 @@ static int count_overhead(struct super_b
 			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;