On Thu, Feb 4, 2016 at 5:59 PM, Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> wrote: > On Thu, Feb 04, 2016 at 05:37:49PM +0100, Dmitry Vyukov wrote: >> On Thu, Feb 4, 2016 at 5:32 PM, Ville Syrjälä >> <ville.syrjala@xxxxxxxxxxxxxxx> wrote: >> > On Thu, Feb 04, 2016 at 04:49:49PM +0100, Dmitry Vyukov wrote: >> >> 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@xxxxxxxxxx> >> >> --- >> >> 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); >> > >> > I don't really see why it does this user controlled malloc in the >> > first place. The max legth of the string it will actually handle looks >> > well bounded, so it could just use some fixed length buffer (on stack >> > even). >> >> >> What would be the right limit on data len? > > From the looks of things the longest command could be the > "target PCI:domain:bus:dev.fn" thing. Even assuming something silly like > having 10 characters for each domain,bus,dev,fn that would still be only > 55 bytes. So based on that even something like 64 bytes should be more > than enough AFAICS. David, what do you think? I can allocate char kbuf[64] on stack. > The other thing that strikes me as bit odd in this code is that it > just ignores whatever data is left over after it's done parsing the > string. But it returns the full count to userspace, indicating it > ate all of it. I guess that's fairly sane when userspace just uses a > fixed size buffer and checks that the kernel consumed it all. But > maybe there should be an actual check to see that there's a '\0' > or maybe <any amount of whitespace>+'\0' after the parsed string. _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/dri-devel
