linux-kernel - drivers/md/dm-integrity.c:521 sb_mac() error: __builtin_memcmp() 'actual

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Message-ID: <e8c80d61-2c74-4b50-ab50-2cf1291df9bc@stanley.mountain>
Date: Tue, 10 Sep 2024 10:31:56 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: oe-kbuild@...ts.linux.dev, Eric Biggers <ebiggers@...gle.com>
Cc: lkp@...el.com, oe-kbuild-all@...ts.linux.dev,
	linux-kernel@...r.kernel.org, Mike Snitzer <snitzer@...nel.org>
Subject: drivers/md/dm-integrity.c:521 sb_mac() error: __builtin_memcmp()
 'actual_mac' too small (64 vs 448)

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
head:   b831f83e40a24f07c8dcba5be408d93beedc820f
commit: 070bb43ab01e891db1b742d4ddd7291c7f8d7022 dm integrity: use crypto_shash_digest() in sb_mac()
date:   10 months ago
config: i386-randconfig-141-20240906 (https://download.01.org/0day-ci/archive/20240906/202409061401.44rtN1bh-lkp@intel.com/config)
compiler: clang version 18.1.5 (https://github.com/llvm/llvm-project 617a15a9eac96088ae5e9134248d8236e34b91b1)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@...el.com>
| Reported-by: Dan Carpenter <dan.carpenter@...aro.org>
| Closes: https://lore.kernel.org/r/202409061401.44rtN1bh-lkp@intel.com/

smatch warnings:
drivers/md/dm-integrity.c:521 sb_mac() error: __builtin_memcmp() 'actual_mac' too small (64 vs 448)

vim +/actual_mac +521 drivers/md/dm-integrity.c

09d85f8d8909ec Mikulas Patocka   2021-01-21  492  static int sb_mac(struct dm_integrity_c *ic, bool wr)
09d85f8d8909ec Mikulas Patocka   2021-01-21  493  {
09d85f8d8909ec Mikulas Patocka   2021-01-21  494  	SHASH_DESC_ON_STACK(desc, ic->journal_mac);
09d85f8d8909ec Mikulas Patocka   2021-01-21  495  	int r;
070bb43ab01e89 Eric Biggers      2023-10-28  496  	unsigned int mac_size = crypto_shash_digestsize(ic->journal_mac);
070bb43ab01e89 Eric Biggers      2023-10-28  497  	__u8 *sb = (__u8 *)ic->sb;
070bb43ab01e89 Eric Biggers      2023-10-28  498  	__u8 *mac = sb + (1 << SECTOR_SHIFT) - mac_size;
09d85f8d8909ec Mikulas Patocka   2021-01-21  499  
070bb43ab01e89 Eric Biggers      2023-10-28  500  	if (sizeof(struct superblock) + mac_size > 1 << SECTOR_SHIFT) {

This is paired with the line before and prevents the subtraction from going
negative.  It limits the mac_size to 0-448.  Is it reasonable to have a mac_size
which is > HASH_MAX_DIGESTSIZE (64)?

09d85f8d8909ec Mikulas Patocka   2021-01-21  501  		dm_integrity_io_error(ic, "digest is too long", -EINVAL);
09d85f8d8909ec Mikulas Patocka   2021-01-21  502  		return -EINVAL;
09d85f8d8909ec Mikulas Patocka   2021-01-21  503  	}
09d85f8d8909ec Mikulas Patocka   2021-01-21  504  
09d85f8d8909ec Mikulas Patocka   2021-01-21  505  	desc->tfm = ic->journal_mac;
09d85f8d8909ec Mikulas Patocka   2021-01-21  506  
09d85f8d8909ec Mikulas Patocka   2021-01-21  507  	if (likely(wr)) {
070bb43ab01e89 Eric Biggers      2023-10-28  508  		r = crypto_shash_digest(desc, sb, mac - sb, mac);
09d85f8d8909ec Mikulas Patocka   2021-01-21  509  		if (unlikely(r < 0)) {
070bb43ab01e89 Eric Biggers      2023-10-28  510  			dm_integrity_io_error(ic, "crypto_shash_digest", r);
09d85f8d8909ec Mikulas Patocka   2021-01-21  511  			return r;
09d85f8d8909ec Mikulas Patocka   2021-01-21  512  		}
09d85f8d8909ec Mikulas Patocka   2021-01-21  513  	} else {
070bb43ab01e89 Eric Biggers      2023-10-28  514  		__u8 actual_mac[HASH_MAX_DIGESTSIZE];

This buffer is only 64 bytes.

0ef0b4717aa684 Heinz Mauelshagen 2023-02-01  515  
070bb43ab01e89 Eric Biggers      2023-10-28  516  		r = crypto_shash_digest(desc, sb, mac - sb, actual_mac);
09d85f8d8909ec Mikulas Patocka   2021-01-21  517  		if (unlikely(r < 0)) {
070bb43ab01e89 Eric Biggers      2023-10-28  518  			dm_integrity_io_error(ic, "crypto_shash_digest", r);
09d85f8d8909ec Mikulas Patocka   2021-01-21  519  			return r;
09d85f8d8909ec Mikulas Patocka   2021-01-21  520  		}
070bb43ab01e89 Eric Biggers      2023-10-28 @521  		if (memcmp(mac, actual_mac, mac_size)) {
                                                                                ^^^^^^^^^^
Read overflow.

09d85f8d8909ec Mikulas Patocka   2021-01-21  522  			dm_integrity_io_error(ic, "superblock mac", -EILSEQ);
82bb85998cc9a3 Michael Weiß      2021-09-04  523  			dm_audit_log_target(DM_MSG_PREFIX, "mac-superblock", ic->ti, 0);
09d85f8d8909ec Mikulas Patocka   2021-01-21  524  			return -EILSEQ;
09d85f8d8909ec Mikulas Patocka   2021-01-21  525  		}
09d85f8d8909ec Mikulas Patocka   2021-01-21  526  	}
09d85f8d8909ec Mikulas Patocka   2021-01-21  527  
09d85f8d8909ec Mikulas Patocka   2021-01-21  528  	return 0;
09d85f8d8909ec Mikulas Patocka   2021-01-21  529  }

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki