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Message-Id: <20231007075148.1759-1-andrew.kanner@gmail.com>
Date: Sat, 7 Oct 2023 10:51:49 +0300
From: Andrew Kanner <andrew.kanner@...il.com>
To: martin.lau@...ux.dev, 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
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,
Andrew Kanner <andrew.kanner@...il.com>
Subject: [PATCH bpf v4] net/xdp: fix zero-size allocation warning in xskq_create()
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
vmalloc_user() -> __vmalloc_node_range().
The issue is reproducible on 32-bit arm kernel.
Reported-and-tested-by: syzbot+fae676d3cf469331fc89@...kaller.appspotmail.com
Closes: https://lore.kernel.org/all/000000000000c84b4705fb31741e@google.com/T/
Link: https://syzkaller.appspot.com/bug?extid=fae676d3cf469331fc89
Reported-by: syzbot+b132693e925cbbd89e26@...kaller.appspotmail.com
Closes: https://lore.kernel.org/all/000000000000e20df20606ebab4f@google.com/T/
Fixes: 9f78bf330a66 ("xsk: support use vaddr as ring")
Signed-off-by: Andrew Kanner <andrew.kanner@...il.com>
---
Notes (akanner):
v4:
- add explanation about SIZE_MAX, suggested by Martin KaFai Lau
<martin.lau@...ux.dev>
v3: https://lore.kernel.org/all/20231005193548.515-1-andrew.kanner@gmail.com/T/
- free kzalloc-ed memory before return, the leak was noticed by
Daniel Borkmann <daniel@...earbox.net>
v2: https://lore.kernel.org/all/20231002222939.1519-1-andrew.kanner@gmail.com/raw
- use unlikely() optimization for the case with SIZE_MAX return from
struct_size(), suggested by Alexander Lobakin
<aleksander.lobakin@...el.com>
- cc-ed 4 more maintainers, mentioned by cc_maintainers patchwork
test
v1: https://lore.kernel.org/all/20230928204440.543-1-andrew.kanner@gmail.com/T/
- RFC notes:
It was found that net/xdp/xsk.c:xsk_setsockopt() uses
copy_from_sockptr() to get the number of entries (int) for cases
with XDP_RX_RING / XDP_TX_RING and XDP_UMEM_FILL_RING /
XDP_UMEM_COMPLETION_RING.
Next in xsk_init_queue() there're 2 sanity checks (entries == 0)
and (!is_power_of_2(entries)) for which -EINVAL will be returned.
After that net/xdp/xsk_queue.c:xskq_create() will calculate the
size multipling the number of entries (int) with the size of u64,
at least.
I wonder if there should be the upper bound (e.g. the 3rd sanity
check inside xsk_init_queue()). It seems that without the upper
limit it's quiet easy to overflow the allocated size (SIZE_MAX),
especially for 32-bit architectures, for example arm nodes which
were used by the syzkaller.
In this patch I added a naive check for SIZE_MAX which helped to
skip zero-size allocation after overflow, but maybe it's not quite
right. Please, suggest if you have any thoughts about the
appropriate limit for the size of these xdp rings.
PS: the initial number of entries is 0x20000000 in syzkaller
repro: syscall(__NR_setsockopt, (intptr_t)r[0], 0x11b, 3,
0x20000040, 0x20);
Link:
https://syzkaller.appspot.com/text?tag=ReproC&x=10910f18280000
net/xdp/xsk_queue.c | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/net/xdp/xsk_queue.c b/net/xdp/xsk_queue.c
index f8905400ee07..d2c264030017 100644
--- a/net/xdp/xsk_queue.c
+++ b/net/xdp/xsk_queue.c
@@ -34,6 +34,16 @@ struct xsk_queue *xskq_create(u32 nentries, bool umem_queue)
q->ring_mask = nentries - 1;
size = xskq_get_ring_size(q, umem_queue);
+
+ /* size which is overflowing or close to SIZE_MAX will become 0 in
+ * PAGE_ALIGN(), checking SIZE_MAX is enough due to the previous
+ * is_power_of_2(), the rest will be handled by vmalloc_user()
+ */
+ if (unlikely(size == SIZE_MAX)) {
+ kfree(q);
+ return NULL;
+ }
+
size = PAGE_ALIGN(size);
q->ring = vmalloc_user(size);
--
2.39.3
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