[PATCH v4 03/10] certs: Fix blacklisted hexadecimal hash string check

[Mickaël Salaün]

From: Mickaël Salaün <mic@xxxxxxxxxxxxxxxxxxx>

When looking for a blacklisted hash, bin2hex() is used to transform a
binary hash to an ascii (lowercase) hexadecimal string.  This string is
then search for in the description of the keys from the blacklist
keyring.  When adding a key to the blacklist keyring,
blacklist_vet_description() checks the hash prefix and the hexadecimal
string, but not that this string is lowercase.  It is then valid to set
hashes with uppercase hexadecimal, which will be silently ignored by the
kernel.

Add an additional check to blacklist_vet_description() to check that
hexadecimal strings are in lowercase.

Cc: David Woodhouse <dwmw2@xxxxxxxxxxxxx>
Signed-off-by: Mickaël Salaün <mic@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
Reviewed-by: Ben Boeckel <mathstuf@xxxxxxxxx>
---

Changes since v2:
* Cherry-pick v1 patch from
  https://lore.kernel.org/lkml/2659836.1607940186@xxxxxxxxxxxxxxxxxxxxxx/
  to rebase on v5.11-rc3.
* Rearrange Cc order.
---
 certs/blacklist.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/certs/blacklist.c b/certs/blacklist.c
index 6514f9ebc943..4e1a58170d5c 100644
--- a/certs/blacklist.c
+++ b/certs/blacklist.c
@@ -37,7 +37,7 @@ static int blacklist_vet_description(const char *desc)
 found_colon:
 	desc++;
 	for (; *desc; desc++) {
-		if (!isxdigit(*desc))
+		if (!isxdigit(*desc) || isupper(*desc))
 			return -EINVAL;
 		n++;
 	}
-- 
2.30.0