lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  PHC 
Open Source and information security mailing list archives
Hash Suite for Android: free password hash cracker in your pocket
[<prev] [next>] [<thread-prev] [day] [month] [year] [list]
Date:	Thu, 6 Jun 2013 11:02:55 +0300
From:	Ruslan Bilovol <>
To:	"Theodore Ts'o" <>,
	Ruslan Bilovol <>,,,
Subject: Re: [PATCH 1/2] jbd2: check bh->b_data for NULL in
 jbd2_journal_get_descriptor_buffer before memset()

Hi Ted,

On Tue, Jun 4, 2013 at 4:37 PM, Theodore Ts'o <> wrote:
> On Tue, Jun 04, 2013 at 02:15:57PM +0300, Ruslan Bilovol wrote:
>> > Have you actually seen a case where bh is non-NULL, but bh->b_data is
>> > NULL?  If not, it might be better to do something like this:
>> Yes, this is exactly the situation I observe (bh is non-NULL, but
>> bh->b_data is NULL)
> Hmm... so the stack trace you sent in the commit description was one
> where bh->b_data was NULL?  I'm trying to make sure there isn't
> something else going on that we don't understand.
> Could you put some instrumentation in __find_get_block()?  Something like this:
> struct buffer_head *
> __find_get_block(struct block_device *bdev, sector_t block, unsigned size)
> {
>         struct buffer_head *bh = lookup_bh_lru(bdev, block, size);
>         if (bh == NULL) {
>                 bh = __find_get_block_slow(bdev, block);
>                 if (bh->b_data == NULL) {
>                    pr_crit("b_data NULL after find_get_block_slow\n);
>                    WARN_ON(1);
>                 }
>                 if (bh)
>                         bh_lru_install(bh);
>         } else {
>                 if (bh->b_data == NULL) {
>                         pr_crit("b_data NULL after lookup_bh_lru\n");
>                         WARN_ON(1);
>                 }
>         }
>         if (bh)
>                 touch_buffer(bh);
>         return bh;
> }
> ... and then send me the stack trace after running your reproduction
> case.  If it turns out the problem is in __find_get_block_slow(),
> could you put in similar debugging checks there and try to track it
> down?
> I'm pretty sure the case of bh non-NULL and bh->b_data NULL is never
> supposed to happen, and while we could just put a check where you
> suggested, there are plenty of other places which use __getblk(), and
> there may be other bugs that are hiding here.

Yes agree, that's what I told about in my cover letter fir this patch series.
I will debug it with code you mentioned, but the issue appears
very rarely, so I need at lease few days for catching this..


> Regards,
>                                                 - Ted
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to
> More majordomo info at
> Please read the FAQ at

Best regards,
Ruslan Bilvol
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to
More majordomo info at

Powered by blists - more mailing lists