crypto: fix uninit-value in af_alg_free_resources

Syzbot was able to trigger use of uninitialized memory in
af_alg_free_resources.

Bug is caused by missing initialization of rsgl->sgl.need_unpin before
adding to rsgl_list. Then in case of extract_iter_to_sg() failure, rsgl
is left with uninitialized need_unpin which is read during clean up

BUG: KMSAN: uninit-value in af_alg_free_sg crypto/af_alg.c:545 [inline]
BUG: KMSAN: uninit-value in af_alg_free_areq_sgls crypto/af_alg.c:778 [inline]
BUG: KMSAN: uninit-value in af_alg_free_resources+0x3d1/0xf60 crypto/af_alg.c:1117
 af_alg_free_sg crypto/af_alg.c:545 [inline]
 af_alg_free_areq_sgls crypto/af_alg.c:778 [inline]
 af_alg_free_resources+0x3d1/0xf60 crypto/af_alg.c:1117
 _skcipher_recvmsg crypto/algif_skcipher.c:144 [inline]
...

Uninit was created at:
 slab_post_alloc_hook+0x12f/0xb70 mm/slab.h:767
 slab_alloc_node mm/slub.c:3470 [inline]
 __kmem_cache_alloc_node+0x536/0x8d0 mm/slub.c:3509
 __do_kmalloc_node mm/slab_common.c:984 [inline]
 __kmalloc+0x121/0x3c0 mm/slab_common.c:998
 kmalloc include/linux/slab.h:586 [inline]
 sock_kmalloc+0x128/0x1c0 net/core/sock.c:2683
 af_alg_alloc_areq+0x41/0x2a0 crypto/af_alg.c:1188
 _skcipher_recvmsg crypto/algif_skcipher.c:71 [inline]

Fixes: c1abe6f ("crypto: af_alg: Use extract_iter_to_sg() to create scatterlists")
Reported-and-tested-by: [email protected]
Closes: https://syzkaller.appspot.com/bug?extid=cba21d50095623218389
Signed-off-by: Pavel Skripkin <[email protected]>
Signed-off-by: Herbert Xu <[email protected]>

Author: pskrgag

crypto/af_alg.c

@@ -1241,6 +1241,8 @@ int af_alg_get_rsgl(struct sock *sk, struct msghdr *msg, int flags,
 				return -ENOMEM;
 		}
 
+		rsgl->sgl.need_unpin =
+			iov_iter_extract_will_pin(&msg->msg_iter);
 		rsgl->sgl.sgt.sgl = rsgl->sgl.sgl;
 		rsgl->sgl.sgt.nents = 0;
 		rsgl->sgl.sgt.orig_nents = 0;
@@ -1255,8 +1257,6 @@ int af_alg_get_rsgl(struct sock *sk, struct msghdr *msg, int flags,
 		}
 
 		sg_mark_end(rsgl->sgl.sgt.sgl + rsgl->sgl.sgt.nents - 1);
-		rsgl->sgl.need_unpin =
-			iov_iter_extract_will_pin(&msg->msg_iter);
 
 		/* chain the new scatterlist with previous one */
 		if (areq->last_rsgl)