[PATCH] crypto: AF_ALG - get_page upon reassignment to TX SGL

[Stephan Müller]

Hi Herbert,

The error can be triggered with the following test. Invoking that test
in a while [ 1 ] loop shows that no memory is leaked.

#include <stdio.h>
#include <kcapi.h>

int main(int argc, char *argv[])
{
        char buf[8192];
        struct kcapi_handle *handle;
        struct iovec iov;
        int ret;

        (void)argc;
        (void)argv;

        iov.iov_base = buf;

        ret = kcapi_cipher_init(&handle, "ctr(aes)", 0);
        if (ret)
                return ret;

        ret = kcapi_cipher_setkey(handle, (unsigned char *)"0123456789abcdef", 
16);
        if (ret)
                return ret;

        ret = kcapi_cipher_stream_init_enc(handle, (unsigned char 
*)"0123456789abcdef", NULL, 0);
        if (ret < 0)
                return ret;

        iov.iov_len = 4152;
        ret = kcapi_cipher_stream_update(handle, &iov, 1);
        if (ret < 0)
                return ret;

        iov.iov_len = 4096;
        ret = kcapi_cipher_stream_op(handle, &iov, 1);
        if (ret < 0)
                return ret;

        kcapi_cipher_destroy(handle);

        return 0;
}

---8<---

When a page is assigned to a TX SGL, call get_page to increment the
reference counter. It is possible that one page is referenced in
multiple SGLs:

- in the global TX SGL in case a previous af_alg_pull_tsgl only
reassigned parts of a page to a per-request TX SGL

- in the per-request TX SGL as assigned by af_alg_pull_tsgl

Note, multiple requests can be active at the same time whose TX SGLs all
point to different parts of the same page.

Signed-off-by: Stephan Mueller <smuel...@chronox.de>
---
 crypto/af_alg.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/crypto/af_alg.c b/crypto/af_alg.c
index d6936c0e08d9..ffa9f4ccd9b4 100644
--- a/crypto/af_alg.c
+++ b/crypto/af_alg.c
@@ -641,9 +641,9 @@ void af_alg_pull_tsgl(struct sock *sk, size_t used, struct 
scatterlist *dst,
                                if (dst_offset >= plen) {
                                        /* discard page before offset */
                                        dst_offset -= plen;
-                                       put_page(page);
                                } else {
                                        /* reassign page to dst after offset */
+                                       get_page(page);
                                        sg_set_page(dst + j, page,
                                                    plen - dst_offset,
                                                    sg[i].offset + dst_offset);
@@ -661,9 +661,7 @@ void af_alg_pull_tsgl(struct sock *sk, size_t used, struct 
scatterlist *dst,
                        if (sg[i].length)
                                return;
 
-                       if (!dst)
-                               put_page(page);
-
+                       put_page(page);
                        sg_assign_page(sg + i, NULL);
                }
 
-- 
2.13.4