Re: [PATCH] proc: fix NULL dereference when reading /proc/<pid>/auxv

[Al Viro]

On Wed, Oct 19, 2016 at 09:59:40PM +0800, Leon Yu wrote:
> Reading auxv of any kernel thread results in NULL pointer dereferencing in
> auxv_read() where mm can be NULL or even error code. Fix that by testing mm
> with IS_ERR_OR_NULL() helper. This is also the original behavior changed by
> recent commit c5317167854e ("proc: switch auxv to use of __mem_open()").

What the...  How can it be ERR_PTR(...) after it has passed __mem_open()?
I agree that we ought to check for NULL mm (the only question is whether it's
best done by failing open() or by treating the file as empty), but this
IS_ERR_OR_NULL() is pure cargo-cult, AFAICS.