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When user application calls read() with MSG_PEEK flag to read data of bpf sockmap socket, kernel panic happens at __tcp_bpf_recvmsg+0x12c/0x350. sk_msg is not removed from ingress_msg queue after read out under MSG_PEEK flag is set. Because it's not judged whether sk_msg is the last msg of ingress_msg queue, the next sk_msg may be the head of ingress_msg queue, whose memory address of sg page is invalid. So it's necessary to add check codes to prevent this problem. [20759.125457] BUG: kernel NULL pointer dereference, address: 0000000000000008 [20759.132118] CPU: 53 PID: 51378 Comm: envoy Tainted: G E 5.4.32 #1 [20759.140890] Hardware name: Inspur SA5212M4/YZMB-00370-109, BIOS 4.1.12 06/18/2017 [20759.149734] RIP: 0010:copy_page_to_iter+0xad/0x300 [20759.270877] __tcp_bpf_recvmsg+0x12c/0x350 [20759.276099] tcp_bpf_recvmsg+0x113/0x370 [20759.281137] inet_recvmsg+0x55/0xc0 [20759.285734] __sys_recvfrom+0xc8/0x130 [20759.290566] ? __audit_syscall_entry+0x103/0x130 [20759.296227] ? syscall_trace_enter+0x1d2/0x2d0 [20759.301700] ? __audit_syscall_exit+0x1e4/0x290 [20759.307235] __x64_sys_recvfrom+0x24/0x30 [20759.312226] do_syscall_64+0x55/0x1b0 [20759.316852] entry_SYSCALL_64_after_hwframe+0x44/0xa9 Signed-off-by: dihu <anny.hu@linux.alibaba.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: John Fastabend <john.fastabend@gmail.com> Acked-by: Jakub Sitnicki <jakub@cloudflare.com> Link: https://lore.kernel.org/bpf/20200605084625.9783-1-anny.hu@linux.alibaba.com
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.