linux-kernel - [PATCH] drivers/gpu/vga: use __GFP_NOWARN for user-controlled kmalloc

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Date:	Thu,  4 Feb 2016 16:49:49 +0100
From:	Dmitry Vyukov <dvyukov@...gle.com>
To:	daniel@...ll.ch, airlied@...ux.ie, dri-devel@...ts.freedesktop.org
Cc:	linux-kernel@...r.kernel.org, syzkaller@...glegroups.com,
	kcc@...gle.com, glider@...gle.com,
	Dmitry Vyukov <dvyukov@...gle.com>
Subject: [PATCH] drivers/gpu/vga: use __GFP_NOWARN for user-controlled kmalloc

Size of kmalloc() in vga_arb_write() is controlled by user.
Too large kmalloc() size triggers WARNING message on console.

Use GFP_USER | __GFP_NOWARN for this kmalloc() to not scare admins.

Signed-off-by: Dmitry Vyukov <dvyukov@...gle.com>
---
Example WARNING:

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
---
 drivers/gpu/vga/vgaarb.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/vga/vgaarb.c b/drivers/gpu/vga/vgaarb.c
index f17cb04..d73b85b 100644
--- a/drivers/gpu/vga/vgaarb.c
+++ b/drivers/gpu/vga/vgaarb.c
@@ -923,7 +923,7 @@ static ssize_t vga_arb_write(struct file *file, const char __user *buf,
 	int i;
 
 
-	kbuf = kmalloc(count + 1, GFP_KERNEL);
+	kbuf = kmalloc(count + 1, GFP_USER | __GFP_NOWARN);
 	if (!kbuf)
 		return -ENOMEM;
 
-- 
2.7.0.rc3.207.g0ac5344