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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 References: <20241130-tcp-bpf-sendmsg-v1-0-bae583d014f3@outlook.com> Content-Language: en-US From: Levi Zim In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: SG2PR01CA0189.apcprd01.prod.exchangelabs.com (2603:1096:4:189::15) To MEYP282MB2312.AUSP282.PROD.OUTLOOK.COM (2603:10c6:220:ff::9) X-Microsoft-Original-Message-ID: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: MEYP282MB2312:EE_|SYBP282MB4054:EE_ X-MS-Office365-Filtering-Correlation-Id: 0f3d9ef4-bbcb-43f2-ed77-08dd142fc534 X-Microsoft-Antispam: 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X-MS-Exchange-CrossTenant-RMS-PersistedConsumerOrg: 00000000-0000-0000-0000-000000000000 X-MS-Exchange-Transport-CrossTenantHeadersStamped: SYBP282MB4054 On 2024-12-04 09:01, Cong Wang wrote: > 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. I am also curious about why other people or the CI didn't hit such crash. I just did a search and find only one mention of this bug: https://lore.kernel.org/bpf/20241020110345.1468595-1-zijianzhang@bytedance.com/ Personally when trying to run test_sockmap on Arch Linux 6.12.1 kernel, I get rcu stall instead of this NPE: rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: rcu:         Tasks blocked on level-0 rcu_node (CPUs 0-11): P3378 rcu:         (detected by 0, t=18002 jiffies, g=9525, q=28619 ncpus=12) task:test_sockmap    state:R  running task     stack:0 pid:3378  tgid:3378  ppid:1168   flags:0x00004006 Call Trace:    ? __schedule+0x3b8/0x12b0  ? get_page_from_freelist+0x366/0x1730  ? sysvec_apic_timer_interrupt+0xe/0x90  ? asm_sysvec_apic_timer_interrupt+0x1a/0x20  ? bpf_msg_pop_data+0x41e/0x690  ? mem_cgroup_charge_skmem+0x40/0x60  ? bpf_prog_1fca1a523ce93f38_bpf_prog4+0x23d/0x248  ? sk_psock_msg_verdict+0x99/0x1e0  ? tcp_bpf_sendmsg+0x42d/0x9f0  ? sock_sendmsg+0x109/0x130  ? splice_to_socket+0x359/0x4f0  ? shmem_file_splice_read+0x2cd/0x300  ? direct_splice_actor+0x51/0x130  ? splice_direct_to_actor+0xf0/0x260  ? __pfx_direct_splice_actor+0x10/0x10  ? do_splice_direct+0x77/0xc0  ? __pfx_direct_file_splice_eof+0x10/0x10  ? do_sendfile+0x382/0x440  ? __x64_sys_sendfile64+0xb3/0xd0  ? do_syscall_64+0x82/0x190  ? find_next_iomem_res+0xbe/0x130  ? __pfx_pagerange_is_ram_callback+0x10/0x10  ? walk_system_ram_range+0xa6/0x100  ? __pte_offset_map+0x1b/0x180  ? __pte_offset_map_lock+0x9e/0x130  ? set_ptes.isra.0+0x41/0x90  ? insert_pfn+0xba/0x210  ? vmf_insert_pfn_prot+0x85/0xd0  ? __do_fault+0x30/0x170  ? do_fault+0x303/0x4c0  ? __handle_mm_fault+0x7c2/0xfa0  ? shmem_file_write_iter+0x5b/0x90  ? __count_memcg_events+0x53/0xf0  ? count_memcg_events.constprop.0+0x1a/0x30  ? handle_mm_fault+0x1bb/0x2c0  ? do_user_addr_fault+0x17f/0x620  ? clear_bhb_loop+0x25/0x80  ? clear_bhb_loop+0x25/0x80  ? clear_bhb_loop+0x25/0x80  ? entry_SYSCALL_64_after_hwframe+0x76/0x7e   >>> 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. Thanks for your help. I will double check it.