crypto: algif_skcipher - only call put_page on referenced and used pages

For asynchronous operation, SGs are allocated without a page mapped to
them or with a page that is not used (ref-counted). If the SGL is freed,
the code must only call put_page for an SG if there was a page assigned
and ref-counted in the first place.

This fixes a kernel crash when using io_submit with more than one iocb
using the sendmsg and sendpage (vmsplice/splice) interface.

Cc: <stable@vger.kernel.org>
Signed-off-by: Stephan Mueller <smueller@chronox.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

1 files changed, 7 insertions, 2 deletions

diff --git a/crypto/algif_skcipher.c b/crypto/algif_skcipher.c
index 43839b00fe6c..903605dbc1a5 100644
--- a/crypto/algif_skcipher.c
+++ b/crypto/algif_skcipher.c
@@ -87,8 +87,13 @@ static void skcipher_free_async_sgls(struct skcipher_async_req *sreq)
         }
         sgl = sreq->tsg;
         n = sg_nents(sgl);
-        for_each_sg(sgl, sg, n, i)
-                put_page(sg_page(sg));
+        for_each_sg(sgl, sg, n, i) {
+                struct page *page = sg_page(sg);
+
+                /* some SGs may not have a page mapped */
+                if (page && page_ref_count(page))
+                        put_page(page);
+        }
 
         kfree(sreq->tsg);
 }