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

[Yonghua Zheng]

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_to_pagemap() for checking
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>

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

On Sat, Aug 10, 2013 at 4:33 AM, Naoya Horiguchi
<n-horiguchi@xxxxxxxxxxxxx> wrote:
> 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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