crypto: af_alg/hash: Fix recvmsg() after sendmsg(MSG_MORE)

If an AF_ALG socket bound to a hashing algorithm is sent a zero-length
message with MSG_MORE set and then recvmsg() is called without first
sending another message without MSG_MORE set to end the operation, an oops
will occur because the crypto context and result doesn't now get set up in
advance because hash_sendmsg() now defers that as long as possible in the
hope that it can use crypto_ahash_digest() - and then because the message
is zero-length, it the data wrangling loop is skipped.

Fix this by handling zero-length sends at the top of the hash_sendmsg()
function.  If we're not continuing the previous sendmsg(), then just ignore
the send (hash_recvmsg() will invent something when called); if we are
continuing, then we finalise the request at this point if MSG_MORE is not
set to get any error here, otherwise the send is of no effect and can be
ignored.

Whilst we're at it, remove the code to create a kvmalloc'd scatterlist if
we get more than ALG_MAX_PAGES - this shouldn't happen.

Fixes: c662b043cdca ("crypto: af_alg/hash: Support MSG_SPLICE_PAGES")
Reported-by: syzbot+13a08c0bf4d212766c3c@syzkaller.appspotmail.com
Link: https://lore.kernel.org/r/000000000000b928f705fdeb873a@google.com/
Reported-by: syzbot+14234ccf6d0ef629ec1a@syzkaller.appspotmail.com
Link: https://lore.kernel.org/r/000000000000c047db05fdeb8790@google.com/
Reported-by: syzbot+4e2e47f32607d0f72d43@syzkaller.appspotmail.com
Link: https://lore.kernel.org/r/000000000000bcca3205fdeb87fb@google.com/
Reported-by: syzbot+472626bb5e7c59fb768f@syzkaller.appspotmail.com
Link: https://lore.kernel.org/r/000000000000b55d8805fdeb8385@google.com/
Signed-off-by: David Howells <dhowells@redhat.com>
Reported-and-tested-by: syzbot+6efc50cc1f8d718d6cb7@syzkaller.appspotmail.com
cc: Jens Axboe <axboe@kernel.dk>
cc: Matthew Wilcox <willy@infradead.org>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
Link: https://lore.kernel.org/r/427646.1686913832@warthog.procyon.org.uk
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/crypto/algif_hash.c b/crypto/algif_hash.c
index dfb048c..0ab43e1 100644 (file)
--- a/crypto/algif_hash.c
+++ b/crypto/algif_hash.c
@@ -76,13 +76,30 @@ static int hash_sendmsg(struct socket *sock, struct msghdr *msg,
 
        lock_sock(sk);
        if (!continuing) {
-               if ((msg->msg_flags & MSG_MORE))
-                       hash_free_result(sk, ctx);
+               /* Discard a previous request that wasn't marked MSG_MORE. */
+               hash_free_result(sk, ctx);
+               if (!msg_data_left(msg))
+                       goto done; /* Zero-length; don't start new req */
                need_init = true;
+       } else if (!msg_data_left(msg)) {
+               /*
+                * No data - finalise the prev req if MSG_MORE so any error
+                * comes out here.
+                */
+               if (!(msg->msg_flags & MSG_MORE)) {
+                       err = hash_alloc_result(sk, ctx);
+                       if (err)
+                               goto unlock_free;
+                       ahash_request_set_crypt(&ctx->req, NULL,
+                                               ctx->result, 0);
+                       err = crypto_wait_req(crypto_ahash_final(&ctx->req),
+                                             &ctx->wait);
+                       if (err)
+                               goto unlock_free;
+               }
+               goto done_more;
        }
 
-       ctx->more = false;
-
        while (msg_data_left(msg)) {
                ctx->sgl.sgt.sgl = ctx->sgl.sgl;
                ctx->sgl.sgt.nents = 0;
@@ -93,15 +110,6 @@ static int hash_sendmsg(struct socket *sock, struct msghdr *msg,
                if (npages == 0)
                        goto unlock_free;
 
-               if (npages > ARRAY_SIZE(ctx->sgl.sgl)) {
-                       err = -ENOMEM;
-                       ctx->sgl.sgt.sgl =
-                               kvmalloc(array_size(npages,
-                                                   sizeof(*ctx->sgl.sgt.sgl)),
-                                        GFP_KERNEL);
-                       if (!ctx->sgl.sgt.sgl)
-                               goto unlock_free;
-               }
                sg_init_table(ctx->sgl.sgl, npages);
 
                ctx->sgl.need_unpin = iov_iter_extract_will_pin(&msg->msg_iter);
@@ -150,7 +158,9 @@ static int hash_sendmsg(struct socket *sock, struct msghdr *msg,
                af_alg_free_sg(&ctx->sgl);
        }
 
+done_more:
        ctx->more = msg->msg_flags & MSG_MORE;
+done:
        err = 0;
 unlock:
        release_sock(sk);
@@ -158,6 +168,8 @@ unlock:
 
 unlock_free:
        af_alg_free_sg(&ctx->sgl);
+       hash_free_result(sk, ctx);
+       ctx->more = false;
        goto unlock;
 }