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Message-ID: <7aa47549-5a95-22d7-1d03-ffdd251cec6d@linux.dev>
Date: Thu, 5 Oct 2023 18:00:46 -0700
From: Martin KaFai Lau <martin.lau@...ux.dev>
To: Andrew Kanner <andrew.kanner@...il.com>
Cc: linux-kernel-mentees@...ts.linuxfoundation.org,
netdev@...r.kernel.org, bpf@...r.kernel.org,
linux-kernel@...r.kernel.org,
syzbot+fae676d3cf469331fc89@...kaller.appspotmail.com,
syzbot+b132693e925cbbd89e26@...kaller.appspotmail.com,
bjorn@...nel.org, magnus.karlsson@...el.com,
maciej.fijalkowski@...el.com, jonathan.lemon@...il.com,
davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
pabeni@...hat.com, aleksander.lobakin@...el.com,
xuanzhuo@...ux.alibaba.com, ast@...nel.org, hawk@...nel.org,
john.fastabend@...il.com, daniel@...earbox.net
Subject: Re: [PATCH bpf v3] net/xdp: fix zero-size allocation warning in
xskq_create()
On 10/5/23 12:35 PM, Andrew Kanner wrote:
> Syzkaller reported the following issue:
> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 2807 at mm/vmalloc.c:3247 __vmalloc_node_range (mm/vmalloc.c:3361)
> Modules linked in:
> CPU: 0 PID: 2807 Comm: repro Not tainted 6.6.0-rc2+ #12
> Hardware name: Generic DT based system
> unwind_backtrace from show_stack (arch/arm/kernel/traps.c:258)
> show_stack from dump_stack_lvl (lib/dump_stack.c:107 (discriminator 1))
> dump_stack_lvl from __warn (kernel/panic.c:633 kernel/panic.c:680)
> __warn from warn_slowpath_fmt (./include/linux/context_tracking.h:153 kernel/panic.c:700)
> warn_slowpath_fmt from __vmalloc_node_range (mm/vmalloc.c:3361 (discriminator 3))
> __vmalloc_node_range from vmalloc_user (mm/vmalloc.c:3478)
> vmalloc_user from xskq_create (net/xdp/xsk_queue.c:40)
> xskq_create from xsk_setsockopt (net/xdp/xsk.c:953 net/xdp/xsk.c:1286)
> xsk_setsockopt from __sys_setsockopt (net/socket.c:2308)
> __sys_setsockopt from ret_fast_syscall (arch/arm/kernel/entry-common.S:68)
>
> xskq_get_ring_size() uses struct_size() macro to safely calculate the
> size of struct xsk_queue and q->nentries of desc members. But the
> syzkaller repro was able to set q->nentries with the value initially
> taken from copy_from_sockptr() high enough to return SIZE_MAX by
> struct_size(). The next PAGE_ALIGN(size) is such case will overflow
> the size_t value and set it to 0. This will trigger WARN_ON_ONCE in
Please ignore the pw-bot email. A question just came to my mind after applying.
> diff --git a/net/xdp/xsk_queue.c b/net/xdp/xsk_queue.c
> index f8905400ee07..c7e8bbb12752 100644
> --- a/net/xdp/xsk_queue.c
> +++ b/net/xdp/xsk_queue.c
> @@ -34,6 +34,11 @@ struct xsk_queue *xskq_create(u32 nentries, bool umem_queue)
> q->ring_mask = nentries - 1;
>
> size = xskq_get_ring_size(q, umem_queue);
> + if (unlikely(size == SIZE_MAX)) {
What if "size" is SIZE_MAX-1? Would it still overflow the PAGE_ALIGN below?
> + kfree(q);
> + return NULL;
> + }
> +
> size = PAGE_ALIGN(size);
>
> q->ring = vmalloc_user(size);
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