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Sat, 07 Oct 2023 00:52:48 -0700 (PDT) Received: from localhost.localdomain ([77.222.24.57]) by smtp.gmail.com with ESMTPSA id n24-20020aa7d058000000b0053331f9094dsm3568685edo.52.2023.10.07.00.52.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 07 Oct 2023 00:52:44 -0700 (PDT) From: Andrew Kanner To: martin.lau@linux.dev, bjorn@kernel.org, magnus.karlsson@intel.com, maciej.fijalkowski@intel.com, jonathan.lemon@gmail.com, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, aleksander.lobakin@intel.com, xuanzhuo@linux.alibaba.com, ast@kernel.org, hawk@kernel.org, john.fastabend@gmail.com, daniel@iogearbox.net Cc: linux-kernel-mentees@lists.linuxfoundation.org, netdev@vger.kernel.org, bpf@vger.kernel.org, linux-kernel@vger.kernel.org, syzbot+fae676d3cf469331fc89@syzkaller.appspotmail.com, syzbot+b132693e925cbbd89e26@syzkaller.appspotmail.com, Andrew Kanner Subject: [PATCH bpf v4] net/xdp: fix zero-size allocation warning in xskq_create() Date: Sat, 7 Oct 2023 10:51:49 +0300 Message-Id: <20231007075148.1759-1-andrew.kanner@gmail.com> X-Mailer: git-send-email 2.39.3 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Syzkaller reported the following issue: ------------[ cut here ]------------ WARNING: CPU: 0 PID: 2807 at mm/vmalloc.c:3247 __vmalloc_node_range (mm/vm= alloc.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 kern= el/panic.c:700) warn_slowpath_fmt from __vmalloc_node_range (mm/vmalloc.c:3361 (discrimina= tor 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@syzkaller.appspotmail.c= om Closes: https://lore.kernel.org/all/000000000000c84b4705fb31741e@google.com= /T/ Link: https://syzkaller.appspot.com/bug?extid=3Dfae676d3cf469331fc89 Reported-by: syzbot+b132693e925cbbd89e26@syzkaller.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 Acked-by: Magnus Karlsson --- Notes (akanner): v4: - add explanation about SIZE_MAX, suggested by Martin KaFai Lau v3: https://lore.kernel.org/all/20231005193548.515-1-andrew.kanner@gmai= l.com/T/ - free kzalloc-ed memory before return, the leak was noticed by Daniel Borkmann v2: https://lore.kernel.org/all/20231002222939.1519-1-andrew.kanner@gma= il.com/raw - use unlikely() optimization for the case with SIZE_MAX return from struct_size(), suggested by Alexander Lobakin - cc-ed 4 more maintainers, mentioned by cc_maintainers patchwork test =20 v1: https://lore.kernel.org/all/20230928204440.543-1-andrew.kanner@gmai= l.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. =20 Next in xsk_init_queue() there're 2 sanity checks (entries =3D=3D 0) and (!is_power_of_2(entries)) for which -EINVAL will be returned. =20 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. =20 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. =20 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. =20 PS: the initial number of entries is 0x20000000 in syzkaller repro: syscall(__NR_setsockopt, (intptr_t)r[0], 0x11b, 3, 0x20000040, 0x20); =20 Link: https://syzkaller.appspot.com/text?tag=3DReproC&x=3D10910f18280000 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_qu= eue) q->ring_mask =3D nentries - 1; =20 size =3D 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 =3D=3D SIZE_MAX)) { + kfree(q); + return NULL; + } + size =3D PAGE_ALIGN(size); =20 q->ring =3D vmalloc_user(size); --=20 2.39.3