[PATCH net-next v2] net/xdp: fix zero-size allocation warning in xskq_create()
From: Andrew Kanner
Date: Mon Oct 02 2023 - 18:31:51 EST
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@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://lore.kernel.org/all/000000000000c84b4705fb31741e@xxxxxxxxxx/T/
Link: https://syzkaller.appspot.com/bug?extid=fae676d3cf469331fc89
Fixes: 9f78bf330a66 ("xsk: support use vaddr as ring")
Signed-off-by: Andrew Kanner <andrew.kanner@xxxxxxxxx>
---
Notes (akanner):
v2:
- use unlikely() optimization for the case with SIZE_MAX return from
struct_size(), suggested by Alexander Lobakin
<aleksander.lobakin@xxxxxxxxx>
- cc-ed 4 more maintainers, mentioned by cc_maintainers patchwork
test
v1: https://lore.kernel.org/all/20230928204440.543-1-andrew.kanner@xxxxxxxxx/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 | 3 +++
1 file changed, 3 insertions(+)
diff --git a/net/xdp/xsk_queue.c b/net/xdp/xsk_queue.c
index f8905400ee07..b03d1bfb6978 100644
--- a/net/xdp/xsk_queue.c
+++ b/net/xdp/xsk_queue.c
@@ -34,6 +34,9 @@ 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))
+ return NULL;
+
size = PAGE_ALIGN(size);
q->ring = vmalloc_user(size);
--
2.39.3