Re: BUG: bad usercopy in memdup_user

[Al Viro]

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
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...