crypto: af_alg - Fix race around ctx->rcvused by making it atomic_t

This variable was increased and decreased without any protection.
Result was an occasional misscount and negative wrap around resulting
in false resource allocation failures.

Fixes: 7d2c3f54e6f6 ("crypto: af_alg - remove locking in async callback")
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Stephan Mueller <smueller@chronox.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

4 files changed, 7 insertions, 6 deletions

diff --git a/crypto/af_alg.c b/crypto/af_alg.c
index f1a2caf1b59b..d3f1c431724b 100644
--- a/crypto/af_alg.c
+++ b/crypto/af_alg.c
@@ -664,7 +664,7 @@ void af_alg_free_areq_sgls(struct af_alg_async_req *areq)
         unsigned int i;
 
         list_for_each_entry_safe(rsgl, tmp, &areq->rsgl_list, list) {
-                ctx->rcvused -= rsgl->sg_num_bytes;
+                atomic_sub(rsgl->sg_num_bytes, &ctx->rcvused);
                 af_alg_free_sg(&rsgl->sgl);
                 list_del(&rsgl->list);
                 if (rsgl != &areq->first_rsgl)
@@ -1162,7 +1162,7 @@ int af_alg_get_rsgl(struct sock *sk, struct msghdr *msg, int flags,
 
                 areq->last_rsgl = rsgl;
                 len += err;
-                ctx->rcvused += err;
+                atomic_add(err, &ctx->rcvused);
                 rsgl->sg_num_bytes = err;
                 iov_iter_advance(&msg->msg_iter, err);
         }
diff --git a/crypto/algif_aead.c b/crypto/algif_aead.c
index b73db2b27656..20df8c1b6851 100644
--- a/crypto/algif_aead.c
+++ b/crypto/algif_aead.c
@@ -571,7 +571,7 @@ static int aead_accept_parent_nokey(void *private, struct sock *sk)
         INIT_LIST_HEAD(&ctx->tsgl_list);
         ctx->len = len;
         ctx->used = 0;
-        ctx->rcvused = 0;
+        atomic_set(&ctx->rcvused, 0);
         ctx->more = 0;
         ctx->merge = 0;
         ctx->enc = 0;
diff --git a/crypto/algif_skcipher.c b/crypto/algif_skcipher.c
index baef9bfccdda..c5c47b680152 100644
--- a/crypto/algif_skcipher.c
+++ b/crypto/algif_skcipher.c
@@ -390,7 +390,7 @@ static int skcipher_accept_parent_nokey(void *private, struct sock *sk)
         INIT_LIST_HEAD(&ctx->tsgl_list);
         ctx->len = len;
         ctx->used = 0;
-        ctx->rcvused = 0;
+        atomic_set(&ctx->rcvused, 0);
         ctx->more = 0;
         ctx->merge = 0;
         ctx->enc = 0;
diff --git a/include/crypto/if_alg.h b/include/crypto/if_alg.h
index 38d9c5861ed8..f38227a78eae 100644
--- a/include/crypto/if_alg.h
+++ b/include/crypto/if_alg.h
@@ -18,6 +18,7 @@
 #include <linux/if_alg.h>
 #include <linux/scatterlist.h>
 #include <linux/types.h>
+#include <linux/atomic.h>
 #include <net/sock.h>
 
 #include <crypto/aead.h>
@@ -150,7 +151,7 @@ struct af_alg_ctx {
         struct crypto_wait wait;
 
         size_t used;
-        size_t rcvused;
+        atomic_t rcvused;
 
         bool more;
         bool merge;
@@ -215,7 +216,7 @@ static inline int af_alg_rcvbuf(struct sock *sk)
         struct af_alg_ctx *ctx = ask->private;
 
         return max_t(int, max_t(int, sk->sk_rcvbuf & PAGE_MASK, PAGE_SIZE) -
-                          ctx->rcvused, 0);
+                     atomic_read(&ctx->rcvused), 0);
 }
 
 /**