[PATCH AUTOSEL 6.18] crypto: af_alg - Fix page reassignment overflow in af_alg_pull_tsgl

[Sasha Levin <sashal@kernel.org>]

From: Herbert Xu <herbert@gondor.apana.org.au>

[ Upstream commit 31d00156e50ecad37f2cb6cbf04aaa9a260505ef ]

When page reassignment was added to af_alg_pull_tsgl the original
loop wasn't updated so it may try to reassign one more page than
necessary.

Add the check to the reassignment so that this does not happen.

Also update the comment which still refers to the obsolete offset
argument.

Reported-by: syzbot+d23888375c2737c17ba5@syzkaller.appspotmail.com
Fixes: e870456d8e7c ("crypto: algif_skcipher - overhaul memory management")
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

LLM Generated explanations, may be completely bogus:

Error: Failed to generate final synthesis

 crypto/af_alg.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/crypto/af_alg.c b/crypto/af_alg.c
index 6867d177f2a2d..b61c3ba126ed1 100644
--- a/crypto/af_alg.c
+++ b/crypto/af_alg.c
@@ -705,8 +705,8 @@ void af_alg_pull_tsgl(struct sock *sk, size_t used, struct scatterlist *dst)
 			 * Assumption: caller created af_alg_count_tsgl(len)
 			 * SG entries in dst.
 			 */
-			if (dst) {
-				/* reassign page to dst after offset */
+			if (dst && plen) {
+				/* reassign page to dst */
 				get_page(page);
 				sg_set_page(dst + j, page, plen, sg[i].offset);
 				j++;
-- 
2.53.0