Re: BUG: bad usercopy in memdup_user

[Randy Dunlap]

On 12/19/2017 01:48 PM, Al Viro wrote:
> On Tue, Dec 19, 2017 at 01:36:46PM -0800, Linus Torvalds wrote:
> 
>> I suspect that an "offset and size within the kernel object" value
>> might make sense.  But what does the _pointer_ tell you?
> 
> Well, for example seeing a 0xfffffffffffffff4 where a pointer to object
> must have been is a pretty strong hint to start looking for a way for
> that ERR_PTR(-ENOMEM) having ended up there...  Something like
> 0x6e69622f7273752f is almost certainly a misplaced "/usr/bin", i.e. a

possibly poison values also?

> pathname overwriting whatever it ends up in, etc.  And yes, I have run
> into both of those in real life.
> 
> Debugging the situation when crap value has ended up in place of a
> pointer is certainly a case where you do want to see what exactly has
> ended up in there...


-- 
~Randy