diff options
| author | Mikulas Patocka | 2022-04-25 08:53:29 -0400 |
|---|---|---|
| committer | Mike Snitzer | 2022-05-09 12:34:03 -0400 |
| commit | 567dd8f34560fa221a6343729474536aa7ede4fd (patch) | |
| tree | b6735601f3577a755c95902502ebe253eb9a0909 /drivers/md | |
| parent | d3f2a14b8906df913cb04a706367b012db94a6e8 (diff) | |
dm crypt: make printing of the key constant-time
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>
Diffstat (limited to 'drivers/md')
| -rw-r--r-- | drivers/md/dm-crypt.c | 14 |
1 files changed, 11 insertions, 3 deletions
diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c index fb80539865d7..159c6806c19b 100644 --- a/drivers/md/dm-crypt.c +++ b/drivers/md/dm-crypt.c @@ -3439,6 +3439,11 @@ 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) { @@ -3457,9 +3462,12 @@ static void crypt_status(struct dm_target *ti, status_type_t type, if (cc->key_size > 0) { if (cc->key_string) DMEMIT(":%u:%s", cc->key_size, cc->key_string); - else - for (i = 0; i < cc->key_size; i++) - DMEMIT("%02x", cc->key[i]); + else { + for (i = 0; i < cc->key_size; i++) { + DMEMIT("%c%c", hex2asc(cc->key[i] >> 4), + hex2asc(cc->key[i] & 0xf)); + } + } } else DMEMIT("-"); |