Re: NULL pointer dereference in sysfs_readdir

[Stefan Richter <stefanr@s5r6.in-berlin.de>]

Michael Buesch wrote:
> On Saturday 21 October 2006 23:09, Stefan Richter wrote:
...
>>>> https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=188140
[hard lockups, also one oops: 'Unable to handle kernel NULL pointer
dereference at virtual address 00000020', 'EIP is at sysfs_readdir',
'Process hald']
...
>>> Maybe FC changed some of the structures. I couldn't find
>>> a used structure with an interresting member at offset 00000020, at least.
>> Could be struct sysfs_dirent.s_dentry if I'm counting correctly in
>> http://www.linux-m32r.org/lxr/http/source/include/linux/sysfs.h?v=2.6.16#L68
>> The trace was from 2.6.16.
> 
> Yeah, I found that offset, too, but:
> 
> There is only one usage of s_dentry
> if (next->s_dentry)
> 
> But _before_ that there already comes
> if (!next->s_element)
> 
> So, if "next" was NULL, it would already oops there.

What if "next" became NULL afterwards? I know it's unlikely (but so is
the whole bug, given that we have just one reporter despite the bug's
age), but is it impossible? IOW does sysfs_readdir have any indirect
mutex protection?

Dave, do you patch sysfs datatypes in FC's kernel, or types they include?
-- 
Stefan Richter
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http://arcgraph.de/sr/