[Plinth PATCH]{topost} crypto: Fix race around ctx->rcvused by making it atomic_t

[Jonathan Cameron]

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

Signed-off-by: Jonathan Cameron <jonathan.came...@huawei.com>
Fixes: 2d97591ef43d ("crypto: af_alg - consolidation of duplicate code")
---
The fixes tag is probably not ideal as I'm not 100% sure when this actually
became a bug.  The code in question was introduced in

Fixes: e870456d8e7c ("crypto: algif_skcipher - overhaul memory management")
and related.
rcvused moved in 
Fixes: 2d97591ef43d ("crypto: af_alg - consolidation of duplicate code")
So I have gone with the latter option as that is where it will cleanly apply.
However, it probably doesn't matter as both are present only in the 4.14
final kernel.

 crypto/af_alg.c         | 4 ++--
 crypto/algif_aead.c     | 2 +-
 crypto/algif_skcipher.c | 2 +-
 include/crypto/if_alg.h | 5 +++--
 4 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/crypto/af_alg.c b/crypto/af_alg.c
index 8612aa36a3ef..759cfa678c04 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)
@@ -1173,7 +1173,7 @@ 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 db9378a45296..d3da3b0869f5 100644
--- a/crypto/algif_aead.c
+++ b/crypto/algif_aead.c
@@ -550,7 +550,7 @@ 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 c7c75ef41952..a5b4898f625a 100644
--- a/crypto/algif_skcipher.c
+++ b/crypto/algif_skcipher.c
@@ -388,7 +388,7 @@ 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);
 }
 
 /**
-- 
2.11.0