linux-kernel - [PATCH] FS: Fixed buffer overflow issue in seq

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Date:	Tue, 19 Nov 2013 00:18:41 +0000
From:	"Charley (Hao Chuan) Chu" <charley.chu@...adcom.com>
To:	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"Alexander Viro" <viro@...iv.linux.org.uk>
cc:	"torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: [PATCH] FS: Fixed buffer overflow issue in seq_read()

The buffer count is not initialized when a new buffer is allocated. 

It cause kernel crash with "Unable to handle kernel paging
request..." error in __copy_to_user_std(). It happens when a 
memory allocation failure in the while(1)-loop, which left the 
buffer count (m->count) is larger than buffer size 
(m->size).  

This patch is currently against a linux 3.12 kernel

Signed-off-by: Charley Chu charley.chu@...adcom.com
---
diff --git a/fs/seq_file.c b/fs/seq_file.c
index 1cd2388..480a341 100644
--- a/fs/seq_file.c
+++ b/fs/seq_file.c
@@ -191,6 +191,7 @@ ssize_t seq_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
 
        /* grab buffer if we didn't have one */
        if (!m->buf) {
+               m->count = m->from = 0;
                m->buf = kmalloc(m->size = PAGE_SIZE, GFP_KERNEL);
                if (!m->buf)
                        goto Enomem;



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