[PATCH] dm-crypt: Reject malformed raw keys in crypt_set_key()

[Thorsten Blum <thorsten.blum@linux.dev>]

dm-crypt calculates the raw key size by dividing the hex string length
by two. If the string has an odd number of characters, the key size is
rounded down and hex2bin() only decodes complete byte pairs.

For example, a 33-character raw key string is malformed, but dm-crypt
treats it as a 16-byte key and ignores the last character.

Reject raw key strings whose length does not match the expected number
of hex characters. This restores the trailing character check that was
lost when the open-coded decoder was replaced with hex2bin().

Fixes: e944e03e336f ("dm crypt: replace custom implementation of hex2bin()")
Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
---
 drivers/md/dm-crypt.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c
index 608b617fb817..b7aa3d893303 100644
--- a/drivers/md/dm-crypt.c
+++ b/drivers/md/dm-crypt.c
@@ -2615,6 +2615,9 @@ static int crypt_set_key(struct crypt_config *cc, char *key)
 	kfree_sensitive(cc->key_string);
 	cc->key_string = NULL;
 
+	if (cc->key_size && key_string_len != cc->key_size * 2)
+		goto out;
+
 	/* Decode key from its hex representation. */
 	if (cc->key_size && hex2bin(cc->key, key, cc->key_size) < 0)
 		goto out;