Dear developers and maintainers, We encountered a kernel warning while using our modified Syzkaller. It is tested against linux kernel 6.8-rc7. Kernel config and C repro are attached to this email. The kernel log is listed below. ``` WARNING: CPU: 0 PID: 8286 at kernel/jump_label.c:229 static_key_disable_cpuslocked+0x15e/0x1c0 kernel/jump_label.c:229 Modules linked in: CPU: 0 PID: 8286 Comm: syz-executor393 Not tainted 6.7.0-rc7 #1 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014 RIP: 0010:static_key_disable_cpuslocked+0x15e/0x1c0 kernel/jump_label.c:229 Code: d3 ff 48 c7 c7 a0 cc 0a 8d e8 5e d3 b6 08 5b 5d e9 f7 bd d3 ff e8 f2 bd d3 ff 48 89 ef e8 2a f8 ff ff eb d9 e8 e3 bd d3 ff 90 <0f> 0b 90 eb 8f e8 d8 bd d3 ff 90 48 c7 c6 00 74 b7 8a 48 89 ea 48 RSP: 0018:ffffc90002c4faf0 EFLAGS: 00010293 RAX: 0000000000000000 RBX: 00000000ffffffff RCX: ffffffff81b1568e RDX: ffff888013b5d980 RSI: ffffffff81b156fd RDI: 0000000000000005 RBP: ffffffff8d0c75d0 R08: 0000000000000005 R09: 0000000000000000 R10: 00000000ffffffff R11: 0000000000000000 R12: ffffffff8d0c75d0 R13: ffff8880209fb980 R14: 0000000000000000 R15: ffffffff8211e160 FS: 0000555555e0e3c0(0000) GS:ffff888063a00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f49e210e090 CR3: 000000001a2d4000 CR4: 0000000000750ef0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 PKRU: 55555554 Call Trace: <TASK> static_key_disable+0x1a/0x20 kernel/jump_label.c:243 enabled_store+0x288/0x2040 mm/vmscan.c:5137 kobj_attr_store+0x54/0x80 lib/kobject.c:836 sysfs_kf_write+0x114/0x170 fs/sysfs/file.c:136 kernfs_fop_write_iter+0x337/0x500 fs/kernfs/file.c:334 call_write_iter include/linux/fs.h:2020 [inline] new_sync_write fs/read_write.c:491 [inline] vfs_write+0x96a/0xd80 fs/read_write.c:584 ksys_write+0x122/0x250 fs/read_write.c:637 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0x40/0x110 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x63/0x6b RIP: 0033:0x7f49e208a7bd Code: c3 e8 a7 1f 00 00 0f 1f 80 00 00 00 00 f3 0f 1e fa 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007ffe25660128 EFLAGS: 00000246 ORIG_RAX: 0000000000000001 RAX: ffffffffffffffda RBX: 00007f49e20db078 RCX: 00007f49e208a7bd RDX: 0000000000000002 RSI: 0000000020000080 RDI: 0000000000000004 RBP: 0000000000000000 R08: 00007f49e20dfb55 R09: 00007f49e20dfb55 R10: 00007f49e20dfb55 R11: 0000000000000246 R12: 00000000000207f3 R13: 00007ffe2566013c R14: 00007ffe25660150 R15: 00007ffe25660140 </TASK> ``` We analyzed the cause of this bug. It seems that in function static_key_disable_cpuslocked(), there is a small racing window between two atomic_read(&key->enabled) in line 228 & 229, triggering the WARN_ON_ONCE macro. This might cause function returned without actually disabling the static_key "key". I am not sure if there is any other potential threat here. I searched on web and found that there was a similar bug reported by syzbot several years ago (https://groups.google.com/g/syzkaller-bugs/c/_W3lgRCwlb4/m/TqzyQcPpAQAJ). At that time the fix was in the net instead of kernel/jump_label.c. So I checked the call stack and cc this email to memory management maintainers. Hope there is no confusion. If you have any questions, please contact us. Reported by: Yue Sun <samsun1006219@xxxxxxxxx> Reported by: xingwei lee <xrivendell7@xxxxxxxxx> Best Regards, Yue
Attachment:
config
Description: Binary data
// autogenerated by syzkaller (https://github.com/google/syzkaller) #define _GNU_SOURCE #include <dirent.h> #include <endian.h> #include <errno.h> #include <fcntl.h> #include <signal.h> #include <stdarg.h> #include <stdbool.h> #include <stdint.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <sys/prctl.h> #include <sys/stat.h> #include <sys/syscall.h> #include <sys/types.h> #include <sys/wait.h> #include <time.h> #include <unistd.h> static unsigned long long procid; static void sleep_ms(uint64_t ms) { usleep(ms * 1000); } static uint64_t current_time_ms(void) { struct timespec ts; if (clock_gettime(CLOCK_MONOTONIC, &ts)) exit(1); return (uint64_t)ts.tv_sec * 1000 + (uint64_t)ts.tv_nsec / 1000000; } static bool write_file(const char* file, const char* what, ...) { char buf[1024]; va_list args; va_start(args, what); vsnprintf(buf, sizeof(buf), what, args); va_end(args); buf[sizeof(buf) - 1] = 0; int len = strlen(buf); int fd = open(file, O_WRONLY | O_CLOEXEC); if (fd == -1) return false; if (write(fd, buf, len) != len) { int err = errno; close(fd); errno = err; return false; } close(fd); return true; } static void kill_and_wait(int pid, int* status) { kill(-pid, SIGKILL); kill(pid, SIGKILL); for (int i = 0; i < 100; i++) { if (waitpid(-1, status, WNOHANG | __WALL) == pid) return; usleep(1000); } DIR* dir = opendir("/sys/fs/fuse/connections"); if (dir) { for (;;) { struct dirent* ent = readdir(dir); if (!ent) break; if (strcmp(ent->d_name, ".") == 0 || strcmp(ent->d_name, "..") == 0) continue; char abort[300]; snprintf(abort, sizeof(abort), "/sys/fs/fuse/connections/%s/abort", ent->d_name); int fd = open(abort, O_WRONLY); if (fd == -1) { continue; } if (write(fd, abort, 1) < 0) { } close(fd); } closedir(dir); } else { } while (waitpid(-1, status, __WALL) != pid) { } } static void setup_test() { prctl(PR_SET_PDEATHSIG, SIGKILL, 0, 0, 0); setpgrp(); write_file("/proc/self/oom_score_adj", "1000"); } static void execute_one(void); #define WAIT_FLAGS __WALL static void loop(void) { int iter = 0; for (;; iter++) { int pid = fork(); if (pid < 0) exit(1); if (pid == 0) { setup_test(); execute_one(); exit(0); } int status = 0; uint64_t start = current_time_ms(); for (;;) { if (waitpid(-1, &status, WNOHANG | WAIT_FLAGS) == pid) break; sleep_ms(1); if (current_time_ms() - start < 5000) continue; kill_and_wait(pid, &status); break; } } } uint64_t r[2] = {0xffffffffffffffff, 0xffffffffffffffff}; void execute_one(void) { intptr_t res = 0; memcpy((void*)0x20000180, "/sys/kernel/mm/lru_gen/enabled\000", 31); res = syscall(__NR_openat, /*fd=*/0xffffffffffffff9cul, /*file=*/0x20000180ul, /*flags=*/2ul, /*mode=*/0ul); if (res != -1) r[0] = res; memcpy((void*)0x20000200, "2\000", 2); syscall(__NR_write, /*fd=*/r[0], /*val=*/0x20000200ul, /*len=*/2ul); memcpy((void*)0x20000000, "/sys/kernel/mm/lru_gen/enabled\000", 31); res = syscall(__NR_openat, /*fd=*/0xffffffffffffff9cul, /*file=*/0x20000000ul, /*flags=*/2ul, /*mode=*/0ul); if (res != -1) r[1] = res; memcpy((void*)0x20000080, "0\000", 2); syscall(__NR_write, /*fd=*/r[1], /*val=*/0x20000080ul, /*len=*/2ul); } int main(void) { syscall(__NR_mmap, /*addr=*/0x1ffff000ul, /*len=*/0x1000ul, /*prot=*/0ul, /*flags=*/0x32ul, /*fd=*/-1, /*offset=*/0ul); syscall(__NR_mmap, /*addr=*/0x20000000ul, /*len=*/0x1000000ul, /*prot=*/7ul, /*flags=*/0x32ul, /*fd=*/-1, /*offset=*/0ul); syscall(__NR_mmap, /*addr=*/0x21000000ul, /*len=*/0x1000ul, /*prot=*/0ul, /*flags=*/0x32ul, /*fd=*/-1, /*offset=*/0ul); for (procid = 0; procid < 4; procid++) { if (fork() == 0) { loop(); } } sleep(1000000); return 0; }
