crypto: af_alg - fix backlog handling

If a request is backlogged, it's complete() handler will get called
twice: once with -EINPROGRESS, and once with the final error code.

af_alg's complete handler, unlike other users, does not handle the
-EINPROGRESS but instead always completes the completion that recvmsg()
is waiting on.  This can lead to a return to user space while the
request is still pending in the driver.  If userspace closes the sockets
before the requests are handled by the driver, this will lead to
use-after-frees (and potential crashes) in the kernel due to the tfm
having been freed.

The crashes can be easily reproduced (for example) by reducing the max
queue length in cryptod.c and running the following (from
http://www.chronox.de/libkcapi.html) on AES-NI capable hardware:

 $ while true; do kcapi -x 1 -e -c '__ecb-aes-aesni' \
    -k 00000000000000000000000000000000 \
    -p 00000000000000000000000000000000 >/dev/null & done

Cc: stable@vger.kernel.org
Signed-off-by: Rabin Vincent <rabin.vincent@axis.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

diff --git a/crypto/af_alg.c b/crypto/af_alg.c
index 1fa7bc31be63b9fb774782ebe3fbdaed0b16ff72..4665b79c729ac1d59d699907d3e5c75628231cdb 100644 (file)
--- a/crypto/af_alg.c
+++ b/crypto/af_alg.c
@@ -455,6 +455,9 @@ void af_alg_complete(struct crypto_async_request *req, int err)
 {
        struct af_alg_completion *completion = req->data;
 
+       if (err == -EINPROGRESS)
+               return;
+
        completion->err = err;
        complete(&completion->completion);
 }