crypto: af_alg - wait for data at beginning of recvmsg

The wait for data is a non-atomic operation that can sleep and therefore
potentially release the socket lock. The release of the socket lock
allows another thread to modify the context data structure. The waiting
operation for new data therefore must be called at the beginning of
recvmsg. This prevents a race condition where checks of the members of
the context data structure are performed by recvmsg while there is a
potential for modification of these values.

Fixes: e870456d8e7c ("crypto: algif_skcipher - overhaul memory management")
Fixes: d887c52d6ae4 ("crypto: algif_aead - overhaul memory management")
Reported-by: syzbot <syzkaller@googlegroups.com>
Cc: <stable@vger.kernel.org> # v4.14+
Signed-off-by: Stephan Mueller <smueller@chronox.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

diff --git a/crypto/af_alg.c b/crypto/af_alg.c
index 358749c38894e31481fb0d903c0d1f7504311aa8..f1a2caf1b59babb28ad777556b329ea48a2314a4 100644 (file)
--- a/crypto/af_alg.c
+++ b/crypto/af_alg.c
@@ -1137,12 +1137,6 @@ int af_alg_get_rsgl(struct sock *sk, struct msghdr *msg, int flags,
                if (!af_alg_readable(sk))
                        break;
 
-               if (!ctx->used) {
-                       err = af_alg_wait_for_data(sk, flags);
-                       if (err)
-                               return err;
-               }
-
                seglen = min_t(size_t, (maxsize - len),
                               msg_data_left(msg));
 

diff --git a/crypto/algif_aead.c b/crypto/algif_aead.c
index 805f485ddf1be4711a9d2ec47998964543f1d217..c8a32bef208a657056ccf81e1c60a7e79f87720a 100644 (file)
--- a/crypto/algif_aead.c
+++ b/crypto/algif_aead.c
@@ -111,6 +111,12 @@ static int _aead_recvmsg(struct socket *sock, struct msghdr *msg,
        size_t usedpages = 0;           /* [in]  RX bufs to be used from user */
        size_t processed = 0;           /* [in]  TX bufs to be consumed */
 
+       if (!ctx->used) {
+               err = af_alg_wait_for_data(sk, flags);
+               if (err)
+                       return err;
+       }
+
        /*
         * Data length provided by caller via sendmsg/sendpage that has not
         * yet been processed.

diff --git a/crypto/algif_skcipher.c b/crypto/algif_skcipher.c
index 30cff827dd8fff048fa3e2ca7de770ab73022749..6fb595cd63ac2a9d14fd606210eeb065930e3724 100644 (file)
--- a/crypto/algif_skcipher.c
+++ b/crypto/algif_skcipher.c
@@ -72,6 +72,12 @@ static int _skcipher_recvmsg(struct socket *sock, struct msghdr *msg,
        int err = 0;
        size_t len = 0;
 
+       if (!ctx->used) {
+               err = af_alg_wait_for_data(sk, flags);
+               if (err)
+                       return err;
+       }
+
        /* Allocate cipher request for current operation. */
        areq = af_alg_alloc_areq(sk, sizeof(struct af_alg_async_req) +
                                     crypto_skcipher_reqsize(tfm));