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git-send-email 2.55.0 In-Reply-To: <6a57ad78.9d83364e.246513.0004.GAE@google.com> References: <6a57ad78.9d83364e.246513.0004.GAE@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Hi, In syzbot report, syzbot wrote: >Hello, > >syzbot found the following issue on: > >HEAD commit: a13c140cc289 Linux 7.2-rc3 >git tree: upstream >console output: https://syzkaller.appspot.com/x/log.txt?x=144c3b89580000 >kernel config: https://syzkaller.appspot.com/x/.config?x=d69870d5e052935f >dashboard link: https://syzkaller.appspot.com/bug?extid=44efda9647c52be29d9c >compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44 > >Unfortunately, I don't have any reproducer for this issue yet. > >Downloadable assets: >disk image: https://storage.googleapis.com/syzbot-assets/2052a80016f0/disk-a13c140c.raw.xz >vmlinux: https://storage.googleapis.com/syzbot-assets/0d06ec9d98a4/vmlinux-a13c140c.xz >kernel image: https://storage.googleapis.com/syzbot-assets/8cfe7c92eaf6/bzImage-a13c140c.xz > >IMPORTANT: if you fix the issue, please add the following tag to the commit: >Reported-by: syzbot+44efda9647c52be29d9c@syzkaller.appspotmail.com > >================================================================== >BUG: KASAN: slab-use-after-free in llc_conn_ac_send_sabme_cmd_p_set_x+0x442/0x470 net/llc/llc_c_ac.c:782 >Read of size 1 at addr ffff8880370c8010 by task kworker/u8:0/11804 > >CPU: 0 UID: 0 PID: 11804 Comm: kworker/u8:0 Not tainted syzkaller >0 PREEMPT(full) >Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/10/2026 >Workqueue: events_unbound toggle_allocation_gate >Call Trace: > > __dump_stack lib/dump_stack.c:94 [inline] > dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120 > print_address_description mm/kasan/report.c:378 [inline] > print_report+0x13d/0x4b0 mm/kasan/report.c:482 > kasan_report+0xdf/0x1c0 mm/kasan/report.c:595 > llc_conn_ac_send_sabme_cmd_p_set_x+0x442/0x470 net/llc/llc_c_ac.c:782 > llc_exec_conn_trans_actions net/llc/llc_conn.c:437 [inline] > llc_conn_service net/llc/llc_conn.c:362 [inline] > llc_conn_state_process+0x3ec/0x1480 net/llc/llc_conn.c:66 > llc_process_tmr_ev net/llc/llc_c_ac.c:1442 [inline] > llc_conn_tmr_common_cb+0x2d4/0x880 net/llc/llc_c_ac.c:1325 > call_timer_fn+0x19a/0x610 kernel/time/timer.c:1748 > expire_timers kernel/time/timer.c:1799 [inline] > __run_timers+0x757/0xb00 kernel/time/timer.c:2374 > __run_timer_base kernel/time/timer.c:2386 [inline] > __run_timer_base kernel/time/timer.c:2378 [inline] > run_timer_base+0x114/0x190 kernel/time/timer.c:2395 > run_timer_softirq+0x1a/0x50 kernel/time/timer.c:2405 > handle_softirqs+0x1ea/0x9b0 kernel/softirq.c:622 > __do_softirq kernel/softirq.c:656 [inline] > invoke_softirq kernel/softirq.c:496 [inline] > __irq_exit_rcu+0x162/0x210 kernel/softirq.c:735 > irq_exit_rcu+0x9/0x30 kernel/softirq.c:752 > instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1062 [inline] > sysvec_apic_timer_interrupt+0xa3/0xc0 arch/x86/kernel/apic/apic.c:1062 > > > asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:674 >RIP: 0010:finish_task_switch.isra.0+0x2cd/0x10c0 kernel/sched/core.c:5361 >Code: ab 0a 00 00 41 c7 87 20 0e 00 00 00 00 00 00 e9 47 04 00 00 49 8d 7f 48 e8 30 b4 e6 09 e8 1b a9 3c 00 fb 48 8d bb f8 16 00 00 <48> b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 0f b6 04 02 84 >RSP: 0018:ffffc90005097578 EFLAGS: 00000202 >RAX: 0000000000056db3 RBX: ffff8880741c8000 RCX: 0000000000000040 >RDX: 0000000000000000 RSI: ffffffff8e1a3c59 RDI: ffff8880741c96f8 >RBP: ffffc900050975d0 R08: 0000000000000001 R09: 0000000000000000 >R10: 0000000000000001 R11: 0000000000000000 R12: ffffffff8e891480 >R13: 0000000000000001 R14: ffffffff91227064 R15: ffff8880b843b4c0 > context_switch kernel/sched/core.c:5513 [inline] > __schedule+0x1264/0x6730 kernel/sched/core.c:7234 > preempt_schedule_irq+0x50/0x90 kernel/sched/core.c:7556 > irqentry_exit_to_kernel_mode_preempt include/linux/irq-entry-common.h:468 [inline] > irqentry_exit_to_kernel_mode include/linux/irq-entry-common.h:539 [inline] > irqentry_exit+0x205/0xa00 kernel/entry/common.c:167 > asm_sysvec_reschedule_ipi+0x1a/0x20 arch/x86/include/asm/idtentry.h:679 >RIP: 0010:__sanitizer_cov_trace_pc+0x0/0x70 kernel/kcov.c:210 >Code: 56 e1 5e 00 48 89 df 5b e9 9d 5c 64 00 be 03 00 00 00 5b e9 32 5a 13 03 66 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 0f 1e fa 65 8b 05 85 a3 59 12 48 8b 34 24 65 48 8b 15 61 a3 59 >RSP: 0018:ffffc90005097850 EFLAGS: 00000206 >RAX: 0000000000000000 RBX: ffffc900050979b0 RCX: ffffffff8bb86f00 >RDX: 0000000000008000 RSI: 0000000000000000 RDI: ffff8880741c8000 >RBP: ffffc900050979d4 R08: 0000000000000005 R09: 0000000000000000 >R10: 0000000000008000 R11: 0000000000000000 R12: ffffc900050979fc >R13: 0000000000008000 R14: 0000000000008000 R15: 0000000000000ffa > insn_get_modrm+0xee/0x790 arch/x86/lib/insn.c:396 > insn_get_sib arch/x86/lib/insn.c:466 [inline] > insn_get_displacement+0x2f9/0x960 arch/x86/lib/insn.c:507 > insn_get_immediate+0x84/0x1e00 arch/x86/lib/insn.c:673 > insn_get_length arch/x86/lib/insn.c:745 [inline] > insn_decode+0x21d/0x320 arch/x86/lib/insn.c:784 > __smp_text_poke_batch_add+0x174/0x790 arch/x86/kernel/alternative.c:3103 > arch_jump_label_transform_queue+0xaf/0x120 arch/x86/kernel/jump_label.c:138 > __jump_label_update+0xd7/0x380 kernel/jump_label.c:513 > jump_label_update+0x37a/0x550 kernel/jump_label.c:910 > static_key_disable_cpuslocked+0x162/0x1c0 kernel/jump_label.c:240 > static_key_disable+0x1a/0x20 kernel/jump_label.c:248 > toggle_allocation_gate mm/kfence/core.c:918 [inline] > toggle_allocation_gate+0x149/0x2d0 mm/kfence/core.c:903 > process_one_work+0xa23/0x1940 kernel/workqueue.c:3322 > process_scheduled_works kernel/workqueue.c:3405 [inline] > worker_thread+0x5ef/0xe50 kernel/workqueue.c:3486 > kthread+0x370/0x450 kernel/kthread.c:436 > ret_from_fork+0x72b/0xd50 arch/x86/kernel/process.c:158 > ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 > > >Allocated by task 12543: > kasan_save_stack+0x30/0x50 mm/kasan/common.c:57 > kasan_save_track+0x14/0x30 mm/kasan/common.c:78 > poison_kmalloc_redzone mm/kasan/common.c:398 [inline] > __kasan_kmalloc+0xaa/0xb0 mm/kasan/common.c:415 > kasan_kmalloc include/linux/kasan.h:263 [inline] > __kmalloc_cache_noprof+0x2e5/0x6c0 mm/slub.c:5515 > _kmalloc_noprof include/linux/slab.h:969 [inline] > _kzalloc_noprof include/linux/slab.h:1290 [inline] > llc_sap_alloc net/llc/llc_core.c:29 [inline] > llc_sap_open+0x120/0x3b0 net/llc/llc_core.c:96 > llc_ui_autobind.isra.0+0x2ae/0x580 net/llc/af_llc.c:301 > llc_ui_connect+0x582/0xdb0 net/llc/af_llc.c:498 > __sys_connect_file+0x141/0x1a0 net/socket.c:2135 > __sys_connect+0x141/0x170 net/socket.c:2154 > __do_sys_connect net/socket.c:2160 [inline] > __se_sys_connect net/socket.c:2157 [inline] > __x64_sys_connect+0x72/0xb0 net/socket.c:2157 > do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] > do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94 > entry_SYSCALL_64_after_hwframe+0x77/0x7f > >Freed by task 0: > kasan_save_stack+0x30/0x50 mm/kasan/common.c:57 > kasan_save_track+0x14/0x30 mm/kasan/common.c:78 > kasan_save_free_info+0x3b/0x70 mm/kasan/generic.c:584 > poison_slab_object mm/kasan/common.c:253 [inline] > __kasan_slab_free+0x5f/0x80 mm/kasan/common.c:285 > kasan_slab_free include/linux/kasan.h:235 [inline] > slab_free_hook mm/slub.c:2705 [inline] > __rcu_free_sheaf_prepare+0x5d/0x2f0 mm/slub.c:2956 > rcu_free_sheaf+0x1a/0xe0 mm/slub.c:6004 > rcu_do_batch kernel/rcu/tree.c:2645 [inline] > rcu_core+0x5a2/0x10d0 kernel/rcu/tree.c:2897 > handle_softirqs+0x1ea/0x9b0 kernel/softirq.c:622 > __do_softirq kernel/softirq.c:656 [inline] > invoke_softirq kernel/softirq.c:496 [inline] > __irq_exit_rcu+0x162/0x210 kernel/softirq.c:735 > irq_exit_rcu+0x9/0x30 kernel/softirq.c:752 > instr_sysvec_call_function_single arch/x86/kernel/smp.c:267 [inline] > sysvec_call_function_single+0xa3/0xc0 arch/x86/kernel/smp.c:267 > asm_sysvec_call_function_single+0x1a/0x20 arch/x86/include/asm/idtentry.h:681 > >The buggy address belongs to the object at ffff8880370c8000 > which belongs to the cache kmalloc-2k of size 2048 >The buggy address is located 16 bytes inside of > freed 2048-byte region [ffff8880370c8000, ffff8880370c8800) > >The buggy address belongs to the physical page: >page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff8880370cd000 pfn:0x370c8 >head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0 >flags: 0xfff00000000240(workingset|head|node=0|zone=1|lastcpupid=0x7ff) >page_type: f5(slab) >raw: 00fff00000000240 ffff88813fe22000 ffffea0000c73e10 ffffea0000a2e810 >raw: ffff8880370cd000 0000000800080007 00000000f5000000 0000000000000000 >head: 00fff00000000240 ffff88813fe22000 ffffea0000c73e10 ffffea0000a2e810 >head: ffff8880370cd000 0000000800080007 00000000f5000000 0000000000000000 >head: 00fff00000000003 fffffffffffffe01 00000000ffffffff 00000000ffffffff >head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000008 >page dumped because: kasan: bad access detected >page_owner tracks the page as allocated >page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd2820(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 5615, tgid 5615 (syz-executor), ts 66637688496, free_ts 48968356257 > set_page_owner include/linux/page_owner.h:32 [inline] > post_alloc_hook+0xfd/0x120 mm/page_alloc.c:1859 > prep_new_page mm/page_alloc.c:1867 [inline] > get_page_from_freelist+0xf48/0x3530 mm/page_alloc.c:3946 > __alloc_frozen_pages_noprof+0x299/0x2dc0 mm/page_alloc.c:5304 > alloc_slab_page mm/slub.c:3294 [inline] > allocate_slab mm/slub.c:3408 [inline] > new_slab+0xa2/0x650 mm/slub.c:3454 > refill_objects+0xe3/0x410 mm/slub.c:7338 > refill_sheaf mm/slub.c:2832 [inline] > __pcs_replace_empty_main+0x376/0x680 mm/slub.c:4703 > alloc_from_pcs mm/slub.c:4801 [inline] > slab_alloc_node mm/slub.c:4933 [inline] > __do_kmalloc_node mm/slub.c:5361 [inline] > __kmalloc_node_track_caller_noprof+0x679/0x830 mm/slub.c:5497 > kmalloc_reserve+0xe8/0x350 net/core/skbuff.c:637 > pskb_expand_head+0x249/0x10e0 net/core/skbuff.c:2306 > netlink_trim+0x22d/0x2f0 net/netlink/af_netlink.c:1300 > netlink_broadcast_filtered+0x6d/0xf20 net/netlink/af_netlink.c:1518 > nlmsg_multicast_filtered include/net/netlink.h:1165 [inline] > nlmsg_multicast include/net/netlink.h:1184 [inline] > nlmsg_notify+0xb1/0x290 net/netlink/af_netlink.c:2599 > rtnl_notify net/core/rtnetlink.c:963 [inline] > rtmsg_ifinfo_send net/core/rtnetlink.c:4553 [inline] > rtmsg_ifinfo_event net/core/rtnetlink.c:4569 [inline] > rtmsg_ifinfo_event net/core/rtnetlink.c:4556 [inline] > rtmsg_ifinfo+0x177/0x1b0 net/core/rtnetlink.c:4575 > __dev_notify_flags+0x24c/0x2e0 net/core/dev.c:9789 > rtnl_configure_link+0x1b5/0x280 net/core/rtnetlink.c:3679 > rtnl_newlink_create net/core/rtnetlink.c:3923 [inline] > __rtnl_newlink net/core/rtnetlink.c:4044 [inline] > rtnl_newlink+0x153b/0x2380 net/core/rtnetlink.c:4159 >page last free pid 5271 tgid 5271 stack trace: > reset_page_owner include/linux/page_owner.h:25 [inline] > __free_pages_prepare mm/page_alloc.c:1406 [inline] > __free_frozen_pages+0x79f/0x1090 mm/page_alloc.c:2950 > qlink_free mm/kasan/quarantine.c:163 [inline] > qlist_free_all+0x47/0xf0 mm/kasan/quarantine.c:179 > kasan_quarantine_reduce+0x1a0/0x1f0 mm/kasan/quarantine.c:286 > __kasan_slab_alloc+0x69/0x90 mm/kasan/common.c:350 > kasan_slab_alloc include/linux/kasan.h:253 [inline] > slab_post_alloc_hook mm/slub.c:4612 [inline] > slab_alloc_node mm/slub.c:4945 [inline] > kmem_cache_alloc_node_noprof+0x27d/0x6b0 mm/slub.c:5017 > __alloc_skb+0x140/0x710 net/core/skbuff.c:704 > alloc_skb include/linux/skbuff.h:1384 [inline] > alloc_skb_with_frags+0xdd/0x760 net/core/skbuff.c:6769 > sock_alloc_send_pskb+0x801/0x980 net/core/sock.c:3010 > unix_dgram_sendmsg+0x3c7/0x1810 net/unix/af_unix.c:2136 > unix_seqpacket_sendmsg+0x12a/0x1d0 net/unix/af_unix.c:2537 > sock_sendmsg_nosec net/socket.c:775 [inline] > __sock_sendmsg net/socket.c:790 [inline] > sock_write_iter+0x53a/0x5b0 net/socket.c:1241 > do_iter_readv_writev+0x6f7/0x930 fs/read_write.c:828 > vfs_writev+0x360/0xdd0 fs/read_write.c:1058 > do_writev+0x28a/0x340 fs/read_write.c:1104 > do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] > do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94 > entry_SYSCALL_64_after_hwframe+0x77/0x7f > >Memory state around the buggy address: > ffff8880370c7f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc > ffff8880370c7f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc >>ffff8880370c8000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > ^ > ffff8880370c8080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > ffff8880370c8100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb >================================================================== >---------------- >Code disassembly (best guess), 2 bytes skipped: > 0: 00 00 add %al,(%rax) > 2: 41 c7 87 20 0e 00 00 movl $0x0,0xe20(%r15) > 9: 00 00 00 00 > d: e9 47 04 00 00 jmp 0x459 > 12: 49 8d 7f 48 lea 0x48(%r15),%rdi > 16: e8 30 b4 e6 09 call 0x9e6b44b > 1b: e8 1b a9 3c 00 call 0x3ca93b > 20: fb sti > 21: 48 8d bb f8 16 00 00 lea 0x16f8(%rbx),%rdi >* 28: 48 b8 00 00 00 00 00 movabs $0xdffffc0000000000,%rax <-- trapping instruction > 2f: fc ff df > 32: 48 89 fa mov %rdi,%rdx > 35: 48 c1 ea 03 shr $0x3,%rdx > 39: 0f b6 04 02 movzbl (%rdx,%rax,1),%eax > 3d: 84 .byte 0x84 > > >--- Before I go further, I would like to say that I am relatively new to this subsystem and anything I say must be taken with a grain of salt. If possible, I would like you to educate me further on this topic. I have analyzed this issue and with the limited knowledge I have, I have reached a potential conclusion. Looking at all possible state transitions, nearly every state starts with our function at fault(llc_conn_ac_send_sabme_cmd_p_set_x()). Timers are deleted further back in the state transitions(llc_conn_ac_stop_other_timers()). static const llc_conn_action_t llc_common_actions_2[] = { *[0] = llc_conn_ac_send_sabme_cmd_p_set_x, [1] = llc_conn_ac_start_ack_timer, *[2] = llc_conn_ac_stop_other_timers, [3] = llc_conn_ac_set_retry_cnt_0, [4] = llc_conn_ac_set_cause_flag_1, [5] = NULL, }; That leaves one plausible explanation: There is a potential race condition occurring between 2 or more CPUs. State transitions that use llc_conn_ac_stop_other_timers() use timer_delete() for all timers except the ack_timer. Since timer_delete() does not synchronize the callbacks, if a second CPU attempts a callback concurrently right as the first CPU executed the timer_delete() or before it moves to LLC_CONN_STATE_RESET, it could cause a UAF(or am I mistaken?) If possible, I would like to know if this is the correct cause for the UAF or if I am looking in the wrong place entirely? Thanks, Jeffin.