diff options
| author | Mikulas Patocka <mpatocka@redhat.com> | 2022-04-25 08:53:29 -0400 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2022-06-06 08:19:46 +0200 |
| commit | 49e2a292b3d63d1971f80a929fc806702074559a (patch) | |
| tree | ee04e9bbc45901914e731dd13c304eb22fc14712 | |
| parent | 41f6ea5b9aaa28b740d47ffe995a5013211fdbb0 (diff) | |
dm crypt: make printing of the key constant-time
commit 567dd8f34560fa221a6343729474536aa7ede4fd upstream.
The device mapper dm-crypt target is using scnprintf("%02x", cc->key[i]) to
report the current key to userspace. However, this is not a constant-time
operation and it may leak information about the key via timing, via cache
access patterns or via the branch predictor.
Change dm-crypt's key printing to use "%c" instead of "%02x". Also
introduce hex2asc() that carefully avoids any branching or memory
accesses when converting a number in the range 0 ... 15 to an ascii
character.
Cc: stable@vger.kernel.org
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Tested-by: Milan Broz <gmazyland@gmail.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | drivers/md/dm-crypt.c | 15 |
1 files changed, 11 insertions, 4 deletions
diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c index 0aedd0ebccec..13a5fcca2833 100644 --- a/drivers/md/dm-crypt.c +++ b/drivers/md/dm-crypt.c @@ -1943,6 +1943,11 @@ static int crypt_map(struct dm_target *ti, struct bio *bio) return DM_MAPIO_SUBMITTED; } +static char hex2asc(unsigned char c) +{ + return c + '0' + ((unsigned)(9 - c) >> 4 & 0x27); +} + static void crypt_status(struct dm_target *ti, status_type_t type, unsigned status_flags, char *result, unsigned maxlen) { @@ -1958,10 +1963,12 @@ static void crypt_status(struct dm_target *ti, status_type_t type, case STATUSTYPE_TABLE: DMEMIT("%s ", cc->cipher_string); - if (cc->key_size > 0) - for (i = 0; i < cc->key_size; i++) - DMEMIT("%02x", cc->key[i]); - else + if (cc->key_size > 0) { + for (i = 0; i < cc->key_size; i++) { + DMEMIT("%c%c", hex2asc(cc->key[i] >> 4), + hex2asc(cc->key[i] & 0xf)); + } + } else DMEMIT("-"); DMEMIT(" %llu %s %llu", (unsigned long long)cc->iv_offset, |