Re: gpu: kmalloc size WARNING in vga_arb_write

[Daniel Vetter]

On Tue, Jan 26, 2016 at 11:26:29AM +0100, Dmitry Vyukov wrote:
> Hello,
> 
> I've hit the following warning while running syzkaller fuzzer:
> 
> ------------[ cut here ]------------
> WARNING: CPU: 2 PID: 29322 at mm/page_alloc.c:2999
> __alloc_pages_nodemask+0x7d2/0x1760()
> Modules linked in:
> CPU: 2 PID: 29322 Comm: syz-executor Tainted: G    B           4.5.0-rc1+ #283
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
>  00000000ffffffff ffff880069eff670 ffffffff8299a06d 0000000000000000
>  ffff8800658a4740 ffffffff864985a0 ffff880069eff6b0 ffffffff8134fcf9
>  ffffffff8166de32 ffffffff864985a0 0000000000000bb7 00000000024040c0
> Call Trace:
>  [<     inline     >] __dump_stack lib/dump_stack.c:15
>  [<ffffffff8299a06d>] dump_stack+0x6f/0xa2 lib/dump_stack.c:50
>  [<ffffffff8134fcf9>] warn_slowpath_common+0xd9/0x140 kernel/panic.c:482
>  [<ffffffff8134ff29>] warn_slowpath_null+0x29/0x30 kernel/panic.c:515
>  [<     inline     >] __alloc_pages_slowpath mm/page_alloc.c:2999
>  [<ffffffff8166de32>] __alloc_pages_nodemask+0x7d2/0x1760 mm/page_alloc.c:3253
>  [<ffffffff81745c99>] alloc_pages_current+0xe9/0x450 mm/mempolicy.c:2090
>  [<     inline     >] alloc_pages include/linux/gfp.h:459
>  [<ffffffff81669bb6>] alloc_kmem_pages+0x16/0x100 mm/page_alloc.c:3433
>  [<ffffffff816c20af>] kmalloc_order+0x1f/0x80 mm/slab_common.c:1008
>  [<ffffffff816c212f>] kmalloc_order_trace+0x1f/0x140 mm/slab_common.c:1019
>  [<     inline     >] kmalloc_large include/linux/slab.h:395
>  [<ffffffff81756b24>] __kmalloc+0x2f4/0x340 mm/slub.c:3557
>  [<     inline     >] kmalloc include/linux/slab.h:468
>  [<ffffffff832c65a4>] vga_arb_write+0xd4/0xe40 drivers/gpu/vga/vgaarb.c:926
>  [<ffffffff817a9831>] do_loop_readv_writev+0x141/0x1e0 fs/read_write.c:719
>  [<ffffffff817ad698>] do_readv_writev+0x5f8/0x6e0 fs/read_write.c:849
>  [<ffffffff817ad8b6>] vfs_writev+0x86/0xc0 fs/read_write.c:886
>  [<     inline     >] SYSC_writev fs/read_write.c:919
>  [<ffffffff817b0a21>] SyS_writev+0x111/0x2b0 fs/read_write.c:911
>  [<ffffffff86359636>] entry_SYSCALL_64_fastpath+0x16/0x7a
> arch/x86/entry/entry_64.S:185
> ---[ end trace d543527022b589ec ]---
> 
> 
> vga_arb_write does:
> 
>     kbuf = kmalloc(count + 1, GFP_KERNEL);
> 
> The kmalloc should use GFP_USER|__GFP_NOWARN flags since the size is
> user-controlled.
> 
> On commit 92e963f50fc74041b5e9e744c330dca48e04f08d.

Care to create a patch for this and submit it please? You've done all the
debug work, might as well take credit ;-)

Thanks, Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch