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Date: Mon, 12 Dec 2016 16:00:28 -0500 (EST)
From: Alan Stern <stern@rowland.harvard.edu>
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To: Andrey Konovalov <andreyknvl@google.com>
cc: Felipe Balbi <balbi@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Deepa Dinamani <deepa.kernel@gmail.com>,
        Michal Hocko <mhocko@suse.com>,
        Mathieu Laurendeau <mat.lau@laposte.net>, Bin Liu <b-liu@ti.com>,
        USB list <linux-usb@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        syzkaller <syzkaller@googlegroups.com>,
        Dmitry Vyukov <dvyukov@google.com>, Kostya Serebryany <kcc@google.com>
Subject: Re: usb/gadget: warning in ep_write_iter/__alloc_pages_nodemask
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On Mon, 12 Dec 2016, Andrey Konovalov wrote:

> On Mon, Dec 12, 2016 at 9:31 PM, Andrey Konovalov <andreyknvl@google.com> wrote:
> > Hi!
> >
> > While running the syzkaller fuzzer I've got the following error report.
> >
> > The issue is that the len argument is not checked for being too big.
> >
> > WARNING: CPU: 1 PID: 9935 at mm/page_alloc.c:3511
> > __alloc_pages_nodemask+0x159c/0x1e20
> > Kernel panic - not syncing: panic_on_warn set ...
> >
> > CPU: 1 PID: 9935 Comm: syz-executor0 Not tainted 4.9.0-rc7+ #34
> > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> >  ffff88006949f2c8 ffffffff81f96b8a ffffffff00000200 1ffff1000d293dec
> >  ffffed000d293de4 0000000000000a06 0000000041b58ab3 ffffffff8598b510
> >  ffffffff81f968f8 0000000041b58ab3 ffffffff85942a58 ffffffff81432860
> > Call Trace:
> >  [<     inline     >] __dump_stack lib/dump_stack.c:15
> >  [<ffffffff81f96b8a>] dump_stack+0x292/0x398 lib/dump_stack.c:51
> >  [<ffffffff8168c88e>] panic+0x1cb/0x3a9 kernel/panic.c:179
> >  [<ffffffff812b80b4>] __warn+0x1c4/0x1e0 kernel/panic.c:542
> >  [<ffffffff812b831c>] warn_slowpath_null+0x2c/0x40 kernel/panic.c:585
> >  [<     inline     >] __alloc_pages_slowpath mm/page_alloc.c:3511
> >  [<ffffffff816c08ac>] __alloc_pages_nodemask+0x159c/0x1e20 mm/page_alloc.c:3781
> >  [<ffffffff817cde17>] alloc_pages_current+0x1c7/0x6b0 mm/mempolicy.c:2072
> >  [<     inline     >] alloc_pages include/linux/gfp.h:469
> >  [<ffffffff8172fd8f>] kmalloc_order+0x1f/0x70 mm/slab_common.c:1015
> >  [<ffffffff8172fdff>] kmalloc_order_trace+0x1f/0x160 mm/slab_common.c:1026
> >  [<     inline     >] kmalloc_large include/linux/slab.h:422
> >  [<ffffffff817e01f0>] __kmalloc+0x210/0x2d0 mm/slub.c:3723
> >  [<     inline     >] kmalloc include/linux/slab.h:495
> >  [<ffffffff832262a7>] ep_write_iter+0x167/0xb50
> > drivers/usb/gadget/legacy/inode.c:664
> >  [<     inline     >] new_sync_write fs/read_write.c:499
> >  [<ffffffff817fdcd3>] __vfs_write+0x483/0x760 fs/read_write.c:512
> >  [<ffffffff817ff720>] vfs_write+0x170/0x4e0 fs/read_write.c:560
> >  [<     inline     >] SYSC_write fs/read_write.c:607
> >  [<ffffffff81803b2b>] SyS_write+0xfb/0x230 fs/read_write.c:599
> >  [<ffffffff84f47ec1>] entry_SYSCALL_64_fastpath+0x1f/0xc2
> > Dumping ftrace buffer:
> >    (ftrace buffer empty)
> > Kernel Offset: disabled

I'm not an expert in this area, but it seems like length checking of
I/O operations should be done in a more central location, like the
VFS, rather than in a million different drivers.

Anyway, it's not a big deal if the memory allocation fails.  Users who
try to transfer large amounts of data at once should expect that
sometimes it won't work.

Alan Stern