[PATCH 6.15 231/780] crypto/krb5: Fix change to use SG miter to use offset

[Greg Kroah-Hartman]

6.15-stable review patch.  If anyone has any objections, please let me know.

------------------

From: David Howells <dhowells at redhat.com>

[ Upstream commit eed848871c96d4b5a7b06307755b75abd0cc7a06 ]

The recent patch to make the rfc3961 simplified code use sg_miter rather
than manually walking the scatterlist to hash the contents of a buffer
described by that scatterlist failed to take the starting offset into
account.

This is indicated by the selftests reporting:

    krb5: Running aes128-cts-hmac-sha256-128 mic
    krb5: !!! TESTFAIL crypto/krb5/selftest.c:446
    krb5: MIC mismatch

Fix this by calling sg_miter_skip() before doing the loop to advance
by the offset.

This only affects packet signing modes and not full encryption in RxGK
because, for full encryption, the message digest is handled inside the
authenc and krb5enc drivers.

Note: Nothing in linus/master uses the krb5lib, though the bug is there.
It is used by AF_RXRPC's RxGK implementation in -next, no need to backport.

Fixes: da6f9bf40ac2 ("crypto: krb5 - Use SG miter instead of doing it by hand")
Reported-by: Marc Dionne <marc.dionne at auristor.com>
Signed-off-by: David Howells <dhowells at redhat.com>
cc: Chuck Lever <chuck.lever at oracle.com>
cc: Simon Horman <horms at kernel.org>
cc: linux-afs at lists.infradead.org
Acked-by: Herbert Xu <herbert at gondor.apana.org.au>
Link: https://patch.msgid.link/3824017.1745835726@warthog.procyon.org.uk
Signed-off-by: Jakub Kicinski <kuba at kernel.org>
Signed-off-by: Sasha Levin <sashal at kernel.org>
---
 crypto/krb5/rfc3961_simplified.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/crypto/krb5/rfc3961_simplified.c b/crypto/krb5/rfc3961_simplified.c
index 79180d28baa9f..e49cbdec7c404 100644
--- a/crypto/krb5/rfc3961_simplified.c
+++ b/crypto/krb5/rfc3961_simplified.c
@@ -89,6 +89,7 @@ int crypto_shash_update_sg(struct shash_desc *desc, struct scatterlist *sg,
 
 	sg_miter_start(&miter, sg, sg_nents(sg),
 		       SG_MITER_FROM_SG | SG_MITER_LOCAL);
+	sg_miter_skip(&miter, offset);
 	for (i = 0; i < len; i += n) {
 		sg_miter_next(&miter);
 		n = min(miter.length, len - i);
-- 
2.39.5