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authorMikulas Patocka <mpatocka@redhat.com>2022-04-25 15:53:29 +0300
committerMike Snitzer <snitzer@kernel.org>2022-05-09 19:34:03 +0300
commit567dd8f34560fa221a6343729474536aa7ede4fd (patch)
treeb6735601f3577a755c95902502ebe253eb9a0909 /drivers/md
parentd3f2a14b8906df913cb04a706367b012db94a6e8 (diff)
downloadlinux-567dd8f34560fa221a6343729474536aa7ede4fd.tar.xz
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.c14
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("-");