[PATCH] mm: Don't let userspace spam allocations warnings

[Michal Hocko]

On Wed 20-02-19 21:40:58, Daniel Vetter wrote:
> memdump_user usually gets fed unchecked userspace input. Blasting a
> full backtrace into dmesg every time is a bit excessive - I'm not sure
> on the kernel rule in general, but at least in drm we're trying not to
> let unpriviledge userspace spam the logs freely. Definitely not entire
> warning backtraces.

Yes, this makes sense to me. This API sounds like an example where
returning ENOMEM to the userspace right away is much better than
spamming the log for large allocation requests. Smaller allocations
simply do not fail and the OOM killer report will be printed regardless
of __GFP_NOWARN.

> It also means more filtering for our CI, because our testsuite
> exercises these corner cases and so hits these a lot.
> 
> Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
> Cc: Andrew Morton <akpm at linux-foundation.org>
> Cc: Mike Rapoport <rppt at linux.vnet.ibm.com>
> Cc: Michal Hocko <mhocko at suse.com>
> Cc: Roman Gushchin <guro at fb.com>
> Cc: Vlastimil Babka <vbabka at suse.cz>
> Cc: Jan Stancek <jstancek at redhat.com>
> Cc: Kees Cook <keescook at chromium.org>
> Cc: Andrey Ryabinin <aryabinin at virtuozzo.com>
> Cc: "Michael S. Tsirkin" <mst at redhat.com>
> Cc: Huang Ying <ying.huang at intel.com>
> Cc: Bartosz Golaszewski <brgl at bgdev.pl>
> Cc: linux-mm at kvack.org

Acked-by: Michal Hocko <mhocko at suse.com>

> ---
>  mm/util.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/util.c b/mm/util.c
> index 1ea055138043..379319b1bcfd 100644
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -150,7 +150,7 @@ void *memdup_user(const void __user *src, size_t len)
>  {
>  	void *p;
>  
> -	p = kmalloc_track_caller(len, GFP_USER);
> +	p = kmalloc_track_caller(len, GFP_USER | __GFP_NOWARN);
>  	if (!p)
>  		return ERR_PTR(-ENOMEM);
>  
> -- 
> 2.20.1
> 

-- 
Michal Hocko
SUSE Labs