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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , David Ahern , netdev@vger.kernel.org, bpf@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH net 0/2] Fix NPE discovered by running bpf kselftest Message-ID: References: <20241130-tcp-bpf-sendmsg-v1-0-bae583d014f3@outlook.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Sun, Dec 01, 2024 at 09:42:08AM +0800, Levi Zim wrote: > On 2024-11-30 21:38, Levi Zim via B4 Relay wrote: > > I found that bpf kselftest sockhash::test_txmsg_cork_hangs in > > test_sockmap.c triggers a kernel NULL pointer dereference: Interesting, I also ran this test recently and I didn't see such a crash. > > > > BUG: kernel NULL pointer dereference, address: 0000000000000008 > > ? __die_body+0x6e/0xb0 > > ? __die+0x8b/0xa0 > > ? page_fault_oops+0x358/0x3c0 > > ? local_clock+0x19/0x30 > > ? lock_release+0x11b/0x440 > > ? kernelmode_fixup_or_oops+0x54/0x60 > > ? __bad_area_nosemaphore+0x4f/0x210 > > ? mmap_read_unlock+0x13/0x30 > > ? bad_area_nosemaphore+0x16/0x20 > > ? do_user_addr_fault+0x6fd/0x740 > > ? prb_read_valid+0x1d/0x30 > > ? exc_page_fault+0x55/0xd0 > > ? asm_exc_page_fault+0x2b/0x30 > > ? splice_to_socket+0x52e/0x630 > > ? shmem_file_splice_read+0x2b1/0x310 > > direct_splice_actor+0x47/0x70 > > splice_direct_to_actor+0x133/0x300 > > ? do_splice_direct+0x90/0x90 > > do_splice_direct+0x64/0x90 > > ? __ia32_sys_tee+0x30/0x30 > > do_sendfile+0x214/0x300 > > __se_sys_sendfile64+0x8e/0xb0 > > __x64_sys_sendfile64+0x25/0x30 > > x64_sys_call+0xb82/0x2840 > > do_syscall_64+0x75/0x110 > > entry_SYSCALL_64_after_hwframe+0x4b/0x53 > > > > This is caused by tcp_bpf_sendmsg() returning a larger value(12289) than > > size(8192), which causes the while loop in splice_to_socket() to release > > an uninitialized pipe buf. > > > > The underlying cause is that this code assumes sk_msg_memcopy_from_iter() > > will copy all bytes upon success but it actually might only copy part of > > it. > I am not sure what Fixes tag I should put. Git blame leads me to a refactor > commit > and I am not familiar with this part of code base. Any suggestions? I think it is the following commit which introduced memcopy_from_iter() (which was renamed to sk_msg_memcopy_from_iter() later): commit 4f738adba30a7cfc006f605707e7aee847ffefa0 Author: John Fastabend Date: Sun Mar 18 12:57:10 2018 -0700 bpf: create tcp_bpf_ulp allowing BPF to monitor socket TX/RX data Please double check. Thanks.