[PATCH 2/2] ext2: Check block size validity during mount

[Jan Kara <jack@suse.cz>]

Check that log of block size stored in the superblock has sensible
value. Otherwise the shift computing the block size can overflow leading
to undefined behavior.

Reported-by: syzbot+4fec412f59eba8c01b77@syzkaller.appspotmail.com
Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/ext2/ext2.h  | 1 +
 fs/ext2/super.c | 7 +++++++
 2 files changed, 8 insertions(+)

diff --git a/fs/ext2/ext2.h b/fs/ext2/ext2.h
index 6c8e838bb278..8244366862e4 100644
--- a/fs/ext2/ext2.h
+++ b/fs/ext2/ext2.h
@@ -180,6 +180,7 @@ static inline struct ext2_sb_info *EXT2_SB(struct super_block *sb)
 #define EXT2_MIN_BLOCK_SIZE		1024
 #define	EXT2_MAX_BLOCK_SIZE		65536
 #define EXT2_MIN_BLOCK_LOG_SIZE		  10
+#define EXT2_MAX_BLOCK_LOG_SIZE		  16
 #define EXT2_BLOCK_SIZE(s)		((s)->s_blocksize)
 #define	EXT2_ADDR_PER_BLOCK(s)		(EXT2_BLOCK_SIZE(s) / sizeof (__u32))
 #define EXT2_BLOCK_SIZE_BITS(s)		((s)->s_blocksize_bits)
diff --git a/fs/ext2/super.c b/fs/ext2/super.c
index 69c88facfe90..f342f347a695 100644
--- a/fs/ext2/super.c
+++ b/fs/ext2/super.c
@@ -945,6 +945,13 @@ static int ext2_fill_super(struct super_block *sb, void *data, int silent)
 		goto failed_mount;
 	}
 
+	if (le32_to_cpu(es->s_log_block_size) >
+	    (EXT2_MAX_BLOCK_LOG_SIZE - BLOCK_SIZE_BITS)) {
+		ext2_msg(sb, KERN_ERR,
+			 "Invalid log block size: %u",
+			 le32_to_cpu(es->s_log_block_size));
+		goto failed_mount;
+	}
 	blocksize = BLOCK_SIZE << le32_to_cpu(sbi->s_es->s_log_block_size);
 
 	if (test_opt(sb, DAX)) {
-- 
2.35.3