linux-kernel - Re: [BUG]: mm/vmalloc: uninitialized variable access in pcpu_get_vm

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Message-ID: <457d8e5e453a18faf358bc1360a19003@suse.de>
Date:   Mon, 17 Jun 2019 15:49:51 +0200
From:   Roman Penyaev <rpenyaev@...e.de>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     "Uladzislau Rezki (Sony)" <urezki@...il.com>,
        Roman Gushchin <guro@...com>, Michal Hocko <mhocko@...e.com>,
        Matthew Wilcox <willy@...radead.org>,
        Thomas Garnier <thgarnie@...gle.com>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...ymobile.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Joel Fernandes <joelaf@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...e.hu>, Tejun Heo <tj@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Mike Rapoport <rppt@...ux.ibm.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [BUG]: mm/vmalloc: uninitialized variable access in
 pcpu_get_vm_areas

On 2019-06-17 14:14, Arnd Bergmann wrote:
> gcc points out some obviously broken code in linux-next
> 
> mm/vmalloc.c: In function 'pcpu_get_vm_areas':
> mm/vmalloc.c:991:4: error: 'lva' may be used uninitialized in this
> function [-Werror=maybe-uninitialized]
>     insert_vmap_area_augment(lva, &va->rb_node,
>     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>      &free_vmap_area_root, &free_vmap_area_list);
>      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> mm/vmalloc.c:916:20: note: 'lva' was declared here
>   struct vmap_area *lva;
>                     ^~~
> 
> Remove the obviously broken code. This is almost certainly
> not the correct solution, but it's what I have applied locally
> to get a clean build again.
> 
> Please fix this properly.
> 
> Fixes: 68ad4a330433 ("mm/vmalloc.c: keep track of free blocks for vmap
> allocation")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  mm/vmalloc.c | 7 +------
>  1 file changed, 1 insertion(+), 6 deletions(-)
> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index a9213fc3802d..bfcf0124a773 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -984,14 +984,9 @@ adjust_va_to_fit_type(struct vmap_area *va,
>  		return -1;
>  	}
> 
> -	if (type != FL_FIT_TYPE) {
> +	if (type == FL_FIT_TYPE)
>  		augment_tree_propagate_from(va);
> 
> -		if (type == NE_FIT_TYPE)
> -			insert_vmap_area_augment(lva, &va->rb_node,
> -				&free_vmap_area_root, &free_vmap_area_list);
> -	}
> -
>  	return 0;
>  }


Hi Arnd,

Seems the proper fix is just setting lva to NULL.  The only place
where lva is allocated and then used is when type == NE_FIT_TYPE,
so according to my shallow understanding of the code everything
should be fine.

--
Roman