Re: [PATCH 1/1] pagemap: fix buffer overflow in add_page_map()

[Naoya Horiguchi]

On Fri, Aug 09, 2013 at 01:16:41PM +0800, yonghua zheng wrote:
> Hi,
> 
> Recently we met quite a lot of random kernel panic issues after enable
> CONFIG_PROC_PAGE_MONITOR in kernel, after debuggint sometime we found
> this has something to do with following bug in pagemap:
> 
> In struc pagemapread:
> 
> struct pagemapread {
>     int pos, len;
>     pagemap_entry_t *buffer;
>     bool v2;
> };
> 
> pos is number of PM_ENTRY_BYTES in buffer, but len is the size of buffer,
> it is a mistake to compare pos and len in add_page_map() for checking

s/add_page_map/add_to_pagemap/ ?

> buffer is full or not, and this can lead to buffer overflow and random
> kernel panic issue.
> 
> Correct len to be total number of PM_ENTRY_BYTES in buffer.
> 
> Signed-off-by: Yonghua Zheng <younghua.zheng@xxxxxxxxx>

You can find coding style violation with scripts/checkpatch.pl.
And I think this patch is worth going into -stable trees
(maybe since 2.6.34.)

The fix itself looks fine to me.

Thanks,
Naoya Horiguchi

> ---
>  fs/proc/task_mmu.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index dbf61f6..cb98853 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -1116,8 +1116,8 @@ static ssize_t pagemap_read(struct file *file,
> char __user *buf,
>          goto out_task;
> 
>      pm.v2 = soft_dirty_cleared;
> -    pm.len = PM_ENTRY_BYTES * (PAGEMAP_WALK_SIZE >> PAGE_SHIFT);
> -    pm.buffer = kmalloc(pm.len, GFP_TEMPORARY);
> +    pm.len = (PAGEMAP_WALK_SIZE >> PAGE_SHIFT);
> +    pm.buffer = kmalloc(pm.len * PM_ENTRY_BYTES, GFP_TEMPORARY);
>      ret = -ENOMEM;
>      if (!pm.buffer)
>          goto out_task;
> 
> -- 
> 1.7.9.5
> 
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