[PATCH 3.12 074/127] ext4: sanity check the block and cluster size at mount time

[Jiri Slaby]

From: Theodore Ts'o <tytso@xxxxxxx>

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

===============

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@xxxxxxxxx>
Reported-by: Nikolay Borisov <kernel@xxxxxxxx>
Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
---
 fs/ext4/ext4.h  |  1 +
 fs/ext4/super.c | 17 ++++++++++++++++-
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 66d2dc9ef561..7e80c4dd4735 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -233,6 +233,7 @@ 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
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 584d22c58329..483bc328643d 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -3612,7 +3612,15 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 	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;
 	}
 
@@ -3727,6 +3735,13 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 				 "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 =
-- 
2.10.2