Re: [Jfs-discussion] [PATCH] jfs: Add missing NULL pointer check in __get_metapage

[Dave Kleikamp]

On 10/25/2017 02:50 AM, Juerg Haefliger wrote:
> Is this a patch you might consider?

Sorry it's taken me so long to respond.

I don't think this is the right fix. A failed allocation will still
result in a null pointer dereference by the caller, __get_metapage(). I
think the check needs to be put there. Like this:

--- a/fs/jfs/jfs_metapage.c
+++ b/fs/jfs/jfs_metapage.c
@@ -663,6 +663,8 @@ struct metapage *__get_metapage(struct inode *inode,
unsigned long lblock,
        } else {
                INCREMENT(mpStat.pagealloc);
                mp = alloc_metapage(GFP_NOFS);
+               if (!mp)
+                       goto unlock;
                mp->page = page;
                mp->sb = inode->i_sb;
                mp->flag = 0;


Furthermore, it looks like all the callers of __get_metapage() check for
a null return, so I'm not sure we need to handle the error at this
point. I might have to look a bit harder at that, since there are many
callers.

Thanks,
Shaggy

> 
> Thanks
> ...Juerg
> 
> 
> On 10/04/2017 10:24 AM, Juerg Haefliger wrote:
>> alloc_metapage can return a NULL pointer so check for that. And also emit
>> an error message if that happens.
>>
>> Signed-off-by: Juerg Haefliger <juerg.haefli...@canonical.com>
>> ---
>>  fs/jfs/jfs_metapage.c | 20 +++++++++++++-------
>>  1 file changed, 13 insertions(+), 7 deletions(-)
>>
>> diff --git a/fs/jfs/jfs_metapage.c b/fs/jfs/jfs_metapage.c
>> index 1c4b9ad4d7ab..00f21af66872 100644
>> --- a/fs/jfs/jfs_metapage.c
>> +++ b/fs/jfs/jfs_metapage.c
>> @@ -187,14 +187,18 @@ static inline struct metapage *alloc_metapage(gfp_t 
>> gfp_mask)
>>  {
>>      struct metapage *mp = mempool_alloc(metapage_mempool, gfp_mask);
>>  
>> -    if (mp) {
>> -            mp->lid = 0;
>> -            mp->lsn = 0;
>> -            mp->data = NULL;
>> -            mp->clsn = 0;
>> -            mp->log = NULL;
>> -            init_waitqueue_head(&mp->wait);
>> +    if (!mp) {
>> +            jfs_err("mempool_alloc failed!\n");
>> +            return NULL;
>>      }
>> +
>> +    mp->lid = 0;
>> +    mp->lsn = 0;
>> +    mp->data = NULL;
>> +    mp->clsn = 0;
>> +    mp->log = NULL;
>> +    init_waitqueue_head(&mp->wait);
>> +
>>      return mp;
>>  }
>>  
>> @@ -663,6 +667,8 @@ struct metapage *__get_metapage(struct inode *inode, 
>> unsigned long lblock,
>>      } else {
>>              INCREMENT(mpStat.pagealloc);
>>              mp = alloc_metapage(GFP_NOFS);
>> +            if (!mp)
>> +                    goto unlock;
>>              mp->page = page;
>>              mp->sb = inode->i_sb;
>>              mp->flag = 0;
>>