linux-kernel - [PATCH bpf-next v1 0/3] bpf: Fix FIONREAD and copied

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <20251117110736.293040-1-jiayuan.chen@linux.dev>
Date: Mon, 17 Nov 2025 19:07:04 +0800
From: Jiayuan Chen <jiayuan.chen@...ux.dev>
To: bpf@...r.kernel.org
Cc: jiayuan.chen@...ux.dev,
	John Fastabend <john.fastabend@...il.com>,
	Jakub Sitnicki <jakub@...udflare.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>,
	Neal Cardwell <ncardwell@...gle.com>,
	Kuniyuki Iwashima <kuniyu@...gle.com>,
	David Ahern <dsahern@...nel.org>,
	Andrii Nakryiko <andrii@...nel.org>,
	Eduard Zingerman <eddyz87@...il.com>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Martin KaFai Lau <martin.lau@...ux.dev>,
	Song Liu <song@...nel.org>,
	Yonghong Song <yonghong.song@...ux.dev>,
	KP Singh <kpsingh@...nel.org>,
	Stanislav Fomichev <sdf@...ichev.me>,
	Hao Luo <haoluo@...gle.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Shuah Khan <shuah@...nel.org>,
	Michal Luczaj <mhal@...x.co>,
	Stefano Garzarella <sgarzare@...hat.com>,
	Cong Wang <cong.wang@...edance.com>,
	netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-kselftest@...r.kernel.org
Subject: [PATCH bpf-next v1 0/3] bpf: Fix FIONREAD and copied_seq issues

syzkaller reported a bug [1] where a socket using sockmap, after being
unloaded, exposed incorrect copied_seq calculation. The selftest I
provided can be used to reproduce the issue reported by syzkaller.

TCP recvmsg seq # bug 2: copied E92C873, seq E68D125, rcvnxt E7CEB7C, fl 40
WARNING: CPU: 1 PID: 5997 at net/ipv4/tcp.c:2724 tcp_recvmsg_locked+0xb2f/0x2910 net/ipv4/tcp.c:2724
Call Trace:
 <TASK>
 receive_fallback_to_copy net/ipv4/tcp.c:1968 [inline]
 tcp_zerocopy_receive+0x131a/0x2120 net/ipv4/tcp.c:2200
 do_tcp_getsockopt+0xe28/0x26c0 net/ipv4/tcp.c:4713
 tcp_getsockopt+0xdf/0x100 net/ipv4/tcp.c:4812
 do_sock_getsockopt+0x34d/0x440 net/socket.c:2421
 __sys_getsockopt+0x12f/0x260 net/socket.c:2450
 __do_sys_getsockopt net/socket.c:2457 [inline]
 __se_sys_getsockopt net/socket.c:2454 [inline]
 __x64_sys_getsockopt+0xbd/0x160 net/socket.c:2454
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0xfa0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

A sockmap socket maintains its own receive queue (ingress_msg) which may
contain data from either its own protocol stack or forwarded from other
sockets.

                                                     FD1:read()
                                                     --  FD1->copied_seq++
                                                         |  [read data]
                                                         |
                                [enqueue data]           v
                  [sockmap]     -> ingress to self ->  ingress_msg queue
FD1 native stack  ------>                                 ^
-- FD1->rcv_nxt++               -> redirect to other      | [enqueue data]
                                       |                  |
                                       |             ingress to FD1
                                       v                  ^
                                      ...                 |  [sockmap]
                                                     FD2 native stack

The issue occurs when reading from ingress_msg: we update tp->copied_seq
by default, but if the data comes from other sockets (not the socket's
own protocol stack), tcp->rcv_nxt remains unchanged. Later, when
converting back to a native socket, reads may fail as copied_seq could
be significantly larger than rcv_nxt.

Additionally, FIONREAD calculation based on copied_seq and rcv_nxt is
insufficient for sockmap sockets, requiring separate field tracking.

[1] https://syzkaller.appspot.com/bug?extid=06dbd397158ec0ea4983

Jiayuan Chen (3):
  bpf, sockmap: Fix incorrect copied_seq calculation
  bpf, sockmap: Fix FIONREAD for sockmap
  bpf, selftest: Add tests for FIONREAD and copied_seq

 include/linux/skmsg.h                         |  71 ++++++-
 net/core/skmsg.c                              |  20 +-
 net/ipv4/tcp_bpf.c                            |  26 ++-
 net/ipv4/udp_bpf.c                            |  25 ++-
 .../selftests/bpf/prog_tests/sockmap_basic.c  | 192 +++++++++++++++++-
 .../bpf/progs/test_sockmap_pass_prog.c        |   8 +
 6 files changed, 325 insertions(+), 17 deletions(-)

-- 
2.43.0