Dear Linux Developers, Recently, when using our tool to fuzz kernel, the following crash was triggered. HEAD commit: 76dcd734eca git tree: linux-next compiler: clang 12.0.0 console output: https://drive.google.com/file/d/1mHUUrG4QFkrmP3xw7QgiytT7xWE6lbPy/view?usp=share_link kernel config: https://drive.google.com/file/d/1jH4qV5XblPADvMDUlvS7DwtW0FroMoVB/view?usp=share_link Unfortunately, I do not have a reproducer for this crash. My manual investigation found that the value of %rax may be invalid. When adding statistics to net_statistics of the current network namespace, the value of net->mib (which is %rax) is invalid. I'm wondering if sk or net is freed, which causes an invalid address of mib. IMPORTANT: if you fix the bug, please add the following tag to the commit: Reported-by: Wei Chen <harperchen1110@xxxxxxxxx> BUG: unable to handle page fault for address: ffff88800167981d #PF: supervisor write access in kernel mode #PF: error_code(0x0003) - permissions violation PGD 7201067 P4D 7201067 PUD 7202067 PMD 80000000016001e1 Oops: 0003 [#1] PREEMPT SMP CPU: 0 PID: 1425 Comm: systemd-udevd Not tainted 6.1.0-rc8 #3 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.13.0-48-gd9c812dda519-prebuilt.qemu.org 04/01/2014 RIP: 0010:tcp_xmit_probe_skb net/ipv4/tcp_output.c:4024 [inline] RIP: 0010:tcp_write_wakeup+0x450/0x710 net/ipv4/tcp_output.c:4078 Code: fd 44 89 6d 2c 49 8d 7c 24 30 e8 9b 93 49 fd 49 8b 5c 24 30 48 8d bb c8 01 00 00 e8 8a 93 49 fd 48 8b 83 c8 01 00 00 49 63 cf <65> 48 ff 04 c8 49 8d bc 24 90 05 00 00 e8 ee 8e 49 fd 45 8b 84 24 RSP: 0018:ffffc90000003cb8 EFLAGS: 00010246 RAX: ffffffff83a794b5 RBX: ffff88800bbe8040 RCX: 000000000000006d RDX: 0000000000000855 RSI: 0000000000000000 RDI: ffff88800bbe8208 RBP: ffff88800bb1a000 R08: 000188800bbe820f R09: 0000000000000000 R10: 0001ffffffffffff R11: 000188800bb1a02c R12: ffff8880368d00c0 R13: 00000000ffffffff R14: ffff88800bb1a028 R15: 000000000000006d FS: 00007fa45b07c8c0(0000) GS:ffff88807dc00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: ffff88800167981d CR3: 000000000ac20000 CR4: 00000000003506f0 Call Trace: <IRQ> tcp_send_probe0+0x2c/0x2b0 net/ipv4/tcp_output.c:4093 tcp_probe_timer net/ipv4/tcp_timer.c:393 [inline] tcp_write_timer_handler+0x322/0x4c0 net/ipv4/tcp_timer.c:624 tcp_write_timer+0xb9/0x160 net/ipv4/tcp_timer.c:637 call_timer_fn+0x2e/0x240 kernel/time/timer.c:1474 expire_timers+0x116/0x240 kernel/time/timer.c:1519 __run_timers+0x368/0x410 kernel/time/timer.c:1790 run_timer_softirq+0x2e/0x60 kernel/time/timer.c:1803 __do_softirq+0xf2/0x2c9 kernel/softirq.c:571 __irq_exit_rcu kernel/softirq.c:650 [inline] irq_exit_rcu+0x41/0x70 kernel/softirq.c:662 sysvec_apic_timer_interrupt+0x8d/0xb0 arch/x86/kernel/apic/apic.c:1107 </IRQ> <TASK> asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:649 RIP: 0010:check_kcov_mode kernel/kcov.c:173 [inline] RIP: 0010:write_comp_data kernel/kcov.c:236 [inline] RIP: 0010:__sanitizer_cov_trace_const_cmp4+0x14/0xa0 kernel/kcov.c:304 Code: 12 4d 89 44 fa 18 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 4c 8b 04 24 65 48 8b 14 25 80 ac 01 00 65 8b 05 04 22 da 7e <a9> 00 01 ff 00 74 10 a9 00 01 00 00 74 6e 83 ba c4 0a 00 00 00 74 RSP: 0018:ffffc9000059ba10 EFLAGS: 00000246 RAX: 0000000080000000 RBX: ffff8880090653c0 RCX: 0000000000000000 RDX: ffff888009b60e80 RSI: 0000000000000001 RDI: 0000000000000000 RBP: 0000000000000000 R08: ffffffff818fa64f R09: ffffc9000059ba30 R10: 0001ffffffffffff R11: 00018880095f63f0 R12: 0000000000000001 R13: ffff8880095f63a8 R14: 0000000000000000 R15: ffff8880095f63a8 selinux_inode_permission+0x6f/0x400 security/selinux/hooks.c:3073 security_inode_permission+0x72/0xc0 security/security.c:1326 inode_permission+0xc5/0x460 fs/namei.c:533 may_lookup fs/namei.c:1715 [inline] link_path_walk+0x1b2/0x7e0 fs/namei.c:2262 path_lookupat+0x8b/0x3c0 fs/namei.c:2473 filename_lookup+0x133/0x310 fs/namei.c:2503 vfs_statx+0xa3/0x460 fs/stat.c:229 vfs_fstatat fs/stat.c:267 [inline] vfs_lstat include/linux/fs.h:3304 [inline] __do_sys_newlstat fs/stat.c:423 [inline] __se_sys_newlstat+0x6c/0x270 fs/stat.c:417 __x64_sys_newlstat+0x2d/0x40 fs/stat.c:417 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x63/0xcd RIP: 0033:0x7fa459eef335 Code: 69 db 2b 00 64 c7 00 16 00 00 00 b8 ff ff ff ff c3 0f 1f 40 00 83 ff 01 48 89 f0 77 30 48 89 c7 48 89 d6 b8 06 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 03 f3 c3 90 48 8b 15 31 db 2b 00 f7 d8 64 89 RSP: 002b:00007ffeff53e148 EFLAGS: 00000246 ORIG_RAX: 0000000000000006 RAX: ffffffffffffffda RBX: 000055cd6b8d7780 RCX: 00007fa459eef335 RDX: 00007ffeff53e180 RSI: 00007ffeff53e180 RDI: 000055cd6b8d6780 RBP: 00007ffeff53e240 R08: 00007fa45a1ae248 R09: 0000000000001010 R10: 0000000000000020 R11: 0000000000000246 R12: 000055cd6b8d6780 R13: 000055cd6b8d67a0 R14: 000055cd6b8cabbb R15: 000055cd6b8cabc0 </TASK> Modules linked in: CR2: ffff88800167981d ---[ end trace 0000000000000000 ]--- RIP: 0010:tcp_xmit_probe_skb net/ipv4/tcp_output.c:4024 [inline] RIP: 0010:tcp_write_wakeup+0x450/0x710 net/ipv4/tcp_output.c:4078 Code: fd 44 89 6d 2c 49 8d 7c 24 30 e8 9b 93 49 fd 49 8b 5c 24 30 48 8d bb c8 01 00 00 e8 8a 93 49 fd 48 8b 83 c8 01 00 00 49 63 cf <65> 48 ff 04 c8 49 8d bc 24 90 05 00 00 e8 ee 8e 49 fd 45 8b 84 24 RSP: 0018:ffffc90000003cb8 EFLAGS: 00010246 RAX: ffffffff83a794b5 RBX: ffff88800bbe8040 RCX: 000000000000006d RDX: 0000000000000855 RSI: 0000000000000000 RDI: ffff88800bbe8208 RBP: ffff88800bb1a000 R08: 000188800bbe820f R09: 0000000000000000 R10: 0001ffffffffffff R11: 000188800bb1a02c R12: ffff8880368d00c0 R13: 00000000ffffffff R14: ffff88800bb1a028 R15: 000000000000006d FS: 00007fa45b07c8c0(0000) GS:ffff88807dc00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: ffff88800167981d CR3: 000000000ac20000 CR4: 00000000003506f0 ---------------- Code disassembly (best guess): 0: fd std 1: 44 89 6d 2c mov %r13d,0x2c(%rbp) 5: 49 8d 7c 24 30 lea 0x30(%r12),%rdi a: e8 9b 93 49 fd callq 0xfd4993aa f: 49 8b 5c 24 30 mov 0x30(%r12),%rbx 14: 48 8d bb c8 01 00 00 lea 0x1c8(%rbx),%rdi 1b: e8 8a 93 49 fd callq 0xfd4993aa 20: 48 8b 83 c8 01 00 00 mov 0x1c8(%rbx),%rax 27: 49 63 cf movslq %r15d,%rcx * 2a: 65 48 ff 04 c8 incq %gs:(%rax,%rcx,8) <-- trapping instruction 2f: 49 8d bc 24 90 05 00 lea 0x590(%r12),%rdi 36: 00 37: e8 ee 8e 49 fd callq 0xfd498f2a 3c: 45 rex.RB 3d: 8b .byte 0x8b 3e: 84 .byte 0x84 3f: 24 .byte 0x24 Best, Wei
