linux-kernel - Re: [syzbot] KASAN: null-ptr-deref Read in __free

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Date:   Mon, 21 Mar 2022 09:37:57 +0000
From:   David Howells <dhowells@...hat.com>
To:     "Fabio M. De Francesco" <fmdefrancesco@...il.com>
Cc:     dhowells@...hat.com, christophe.jaillet@...adoo.fr,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] KASAN: null-ptr-deref Read in __free_pages

Fabio M. De Francesco <fmdefrancesco@...il.com> wrote:

> I cannot have any objection, it's up to you to decide :)

Of course you can object.  That's kind of the point of a review;-)

How about the attached instead, then?

David
---
--- a/kernel/watch_queue.c
+++ b/kernel/watch_queue.c
@@ -271,9 +271,8 @@ long watch_queue_set_size(struct pipe_inode_info *pipe, unsigned int nr_notes)
 	return 0;
 
 error_p:
-	for (i = 0; i < nr_pages; i++)
-		if (pages[i])
-			__free_page(pages[i]);
+	while (--i >= 0)
+		__free_page(pages[i]);
 	kfree(pages);
 error:
 	(void) account_pipe_buffers(pipe->user, nr_pages, pipe->nr_accounted);