Patch "crypto: algif_skcipher - only call put_page on referenced and used pages" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

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

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
crypto-algif_skcipher-only-call-put_page-on-referenced-and-used-pages.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Stephan Mueller <[email protected]>
Date: Wed, 16 Aug 2017 11:56:24 +0200
Subject: crypto: algif_skcipher - only call put_page on referenced and used pages

From: Stephan Mueller <[email protected]>

commit 445a582738de6802669aeed9c33ca406c23c3b1f upstream.

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.

---
 crypto/algif_skcipher.c |    9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

@@ -86,8 +86,13 @@ static void skcipher_free_async_sgls(str
 	}
 	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);
 }

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/crypto-algif_skcipher-only-call-put_page-on-referenced-and-used-pages.patch

Nope, this broke the build, sorry. If you want it in 4.4-stable, please provide a backported patch.

thanks,

greg k-h

Hi Greg,

The issue is the missing page_ref_count function which used to be atomic_read(&page->_count).

I am not fully sure how to properly provide a patch for old kernels. Below is a manually created patch that compiles and has the same logic. Please let me know if that patch is not suitable.

Note, this patch is only for 4.4 and earlier.

Thanks

---8<---

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.

---

@@ -86,8 +86,13 @@ static void skcipher_free_async_sgls(str
 	}
 	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 && atomic_read(&page->_count))
+			put_page(page);
+	}
 
 	kfree(sreq->tsg);
 }

That works great, thanks.

This doesn't apply to 3.18-stable, is it needed there?

thanks,

greg k-h

Am Dienstag, 5. September 2017, 08:22:43 CEST schrieb Greg KH:

Hi Greg,

No, it fixes a596999b7ddfe "crypto: algif - change algif_skcipher to be asynchronous"

Thanks a lot.

Ciao
Stephan