[PATCH AUTOSEL 5.10 04/24] ext2: Check block size validity during mount

Sasha Levin
2023-05-04T20:01:34Z

From: Jan Kara <jack@suse.cz>

[ Upstream commit 62aeb94433fcec80241754b70d0d1836d5926b0a ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 5136b7289e8da..f06367cfd7641 100644
--- a/fs/ext2/ext2.h
+++ b/fs/ext2/ext2.h
@@ -177,6 +177,7 @@ static inline struct ext2_sb_info *EXT2_SB(struct super_block *sb)
#define EXT2_MIN_BLOCK_SIZE 1024
#define EXT2_MAX_BLOCK_SIZE 4096
#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 9a6475b2ab28b..ab01ec7ac48c5 100644
--- a/fs/ext2/super.c
+++ b/fs/ext2/super.c
@@ -950,6 +950,13 @@ 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)) {
--
2.39.2