[PATCH 3.2 093/126] ext4: sanity check the block and cluster size at mount time

Ben Hutchings
2017-02-15T22:57:08Z

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

commit 8cdf3372fe8368f56315e66bea9f35053c418093 upstream.

If the block size or cluster size is insane, reject the mount. This
is important for security reasons (although we shouldn't be just
depending on this check).

Ref: http://www.securityfocus.com/archive/1/539661
Ref: https://bugzilla.redhat.com/show_bug.cgi?id=1332506
Reported-by: Borislav Petkov <bp@alien8.de>
Reported-by: Nikolay Borisov <kernel@kyup.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
fs/ext4/ext4.h | 1 +
fs/ext4/super.c | 17 ++++++++++++++++-
2 files changed, 17 insertions(+), 1 deletion(-)

--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -244,6 +244,7 @@ struct ext4_io_submit {
#define EXT4_MAX_BLOCK_SIZE 65536
#define EXT4_MIN_BLOCK_LOG_SIZE 10
#define EXT4_MAX_BLOCK_LOG_SIZE 16
+#define EXT4_MAX_CLUSTER_LOG_SIZE 30
#ifdef __KERNEL__
# define EXT4_BLOCK_SIZE(s) ((s)->s_blocksize)
#else
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -3451,7 +3451,15 @@ static int ext4_fill_super(struct super_
if (blocksize < EXT4_MIN_BLOCK_SIZE ||
blocksize > EXT4_MAX_BLOCK_SIZE) {
ext4_msg(sb, KERN_ERR,
- "Unsupported filesystem blocksize %d", blocksize);
+ "Unsupported filesystem blocksize %d (%d log_block_size)",
+ blocksize, le32_to_cpu(es->s_log_block_size));
+ goto failed_mount;
+ }
+ if (le32_to_cpu(es->s_log_block_size) >
+ (EXT4_MAX_BLOCK_LOG_SIZE - EXT4_MIN_BLOCK_LOG_SIZE)) {
+ ext4_msg(sb, KERN_ERR,
+ "Invalid log block size: %u",
+ le32_to_cpu(es->s_log_block_size));
goto failed_mount;
}

@@ -3568,6 +3576,13 @@ static int ext4_fill_super(struct super_
"block size (%d)", clustersize, blocksize);
goto failed_mount;
}
+ if (le32_to_cpu(es->s_log_cluster_size) >
+ (EXT4_MAX_CLUSTER_LOG_SIZE - EXT4_MIN_BLOCK_LOG_SIZE)) {
+ ext4_msg(sb, KERN_ERR,
+ "Invalid log cluster size: %u",
+ le32_to_cpu(es->s_log_cluster_size));
+ goto failed_mount;
+ }
sbi->s_cluster_bits = le32_to_cpu(es->s_log_cluster_size) -
le32_to_cpu(es->s_log_block_size);
sbi->s_clusters_per_group =