Re: [PATCH] tty: use __GFP_NOWARN for user-controlled kmalloc()

[Peter Hurley <peter@hurleysoftware.com>]

Hi Dmitry,

Just a quick procedural note: tty patches need to be addressed to Greg.


On 02/04/2016 07:55 AM, Dmitry Vyukov wrote:
> Size of kmalloc() in vc_do_resize() is controlled by user.
> Too large kmalloc() size triggers WARNING message on console.
> 
> Use __GFP_NOWARN for this kmalloc() to not scare admins.
> 
> Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
> ---
> Example WARNING:
> 
> WARNING: CPU: 3 PID: 7642 at mm/page_alloc.c:2999
> __alloc_pages_nodemask+0x7d2/0x1760()
> Modules linked in:
> CPU: 3 PID: 7642 Comm: a.out Not tainted 4.4.0+ #276
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
>  00000000ffffffff ffff88006d24f610 ffffffff82999e2d 0000000000000000
>  ffff880060d9af80 ffffffff86475560 ffff88006d24f650 ffffffff81352089
>  ffffffff816721e2 ffffffff86475560 0000000000000bb7 00000000024240c0
> Call Trace:
>  [<     inline     >] __dump_stack lib/dump_stack.c:15
>  [<ffffffff82999e2d>] dump_stack+0x6f/0xa2 lib/dump_stack.c:50
>  [<ffffffff81352089>] warn_slowpath_common+0xd9/0x140 kernel/panic.c:482
>  [<ffffffff813522b9>] warn_slowpath_null+0x29/0x30 kernel/panic.c:515
>  [<     inline     >] __alloc_pages_slowpath mm/page_alloc.c:2999
>  [<ffffffff816721e2>] __alloc_pages_nodemask+0x7d2/0x1760 mm/page_alloc.c:3253
>  [<ffffffff8174a799>] alloc_pages_current+0xe9/0x450 mm/mempolicy.c:2090
>  [<     inline     >] alloc_pages include/linux/gfp.h:459
>  [<ffffffff8166df66>] alloc_kmem_pages+0x16/0x100 mm/page_alloc.c:3433
>  [<ffffffff816c698f>] kmalloc_order+0x1f/0x80 mm/slab_common.c:1008
>  [<ffffffff816c6a0f>] kmalloc_order_trace+0x1f/0x140 mm/slab_common.c:1019
>  [<     inline     >] kmalloc_large include/linux/slab.h:395
>  [<ffffffff8175b624>] __kmalloc+0x2f4/0x340 mm/slub.c:3557
>  [<     inline     >] kmalloc include/linux/slab.h:468
>  [<ffffffff82d47800>] vc_do_resize+0x2c0/0x1140 drivers/tty/vt/vt.c:874
>  [<ffffffff82d4878a>] vt_resize+0xaa/0xe0 drivers/tty/vt/vt.c:993
>  [<     inline     >] tiocswinsz drivers/tty/tty_io.c:2357
>  [<ffffffff82cf22b3>] tty_ioctl+0x1083/0x2160 drivers/tty/tty_io.c:2869
>  [<     inline     >] vfs_ioctl fs/ioctl.c:43
>  [<ffffffff817efdac>] do_vfs_ioctl+0x18c/0xfb0 fs/ioctl.c:674
>  [<     inline     >] SYSC_ioctl fs/ioctl.c:689
>  [<ffffffff817f0c5f>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:680
> ---
>  drivers/tty/vt/vt.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
> index bd51bdd..2382810 100644
> --- a/drivers/tty/vt/vt.c
> +++ b/drivers/tty/vt/vt.c
> @@ -871,7 +871,7 @@ static int vc_do_resize(struct tty_struct *tty, struct vc_data *vc,
>  	if (new_cols == vc->vc_cols && new_rows == vc->vc_rows)
>  		return 0;
>  
> -	newscreen = kmalloc(new_screen_size, GFP_USER);
> +	newscreen = kmalloc(new_screen_size, GFP_USER | __GFP_NOWARN);
>  	if (!newscreen)
>  		return -ENOMEM;
>  
>