Messages in this thread | | | Subject | Re: [Jfs-discussion] [PATCH] jfs: Add missing NULL pointer check in __get_metapage | From | Juerg Haefliger <> | Date | Thu, 2 Nov 2017 14:43:42 +0100 |
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On 11/02/2017 02:15 PM, Dave Kleikamp wrote: > On 11/02/2017 01:59 AM, Juerg Haefliger wrote: >> >> >> On 10/30/2017 11:13 PM, Dave Kleikamp wrote: >>> 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; >> >> I don't understand. This is part of the patch that I sent. > > Doh! How'd I miss that?
:-)
>> >> >>> >>> 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. >> >> I don't understand this either :-) Yes, the callers do check for a null >> pointer but things blow up (in __get_metapage) before that check without >> the above fix. > > Yeah, the fix to __get_metapage() is necessary. I'm not convinced the > first part of the patch, to alloc_metapage(), is necessary.
It's not. I just thought it'd be nice to get some sort of notification in the log when the alloc fails. But if the callers log it then that's fine.
...Juerg
>> >> ...Juerg >> >> >>> >>> 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.haefliger@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; >>>>> >>
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