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BUG: KCSAN: data-race in __bpf_get_stackid / bcmp

write to 0xffff888116762190 of 120 bytes by task 16678 on cpu 1:
 __bpf_get_stackid+0x761/0x800 kernel/bpf/stackmap.c:288
 ____bpf_get_stackid kernel/bpf/stackmap.c:324 [inline]
 bpf_get_stackid+0xee/0x120 kernel/bpf/stackmap.c:300
 ____bpf_get_stackid_raw_tp kernel/trace/bpf_trace.c:1810 [inline]
 bpf_get_stackid_raw_tp+0xf6/0x120 kernel/trace/bpf_trace.c:1799
 bpf_prog_e6fc920cfeff8120+0x2a/0x32
 bpf_dispatcher_nop_func include/linux/bpf.h:1332 [inline]
 __bpf_prog_run include/linux/filter.h:718 [inline]
 bpf_prog_run include/linux/filter.h:725 [inline]
 __bpf_trace_run kernel/trace/bpf_trace.c:2257 [inline]
 bpf_trace_run2+0x107/0x1c0 kernel/trace/bpf_trace.c:2298
 __traceiter_kfree+0x2e/0x50 include/trace/events/kmem.h:94
 __do_trace_kfree include/trace/events/kmem.h:94 [inline]
 trace_kfree include/trace/events/kmem.h:94 [inline]
 kfree+0x27b/0x320 mm/slub.c:4866
 netdev_napi_exit net/core/dev.c:11936 [inline]
 free_netdev+0x2b8/0x4a0 net/core/dev.c:11973
 netdev_run_todo+0x711/0x810 net/core/dev.c:11508
 rtnl_unlock+0xe/0x20 net/core/rtnetlink.c:157
 tun_detach drivers/net/tun.c:640 [inline]
 tun_chr_close+0x8c/0x100 drivers/net/tun.c:3433
 __fput+0x298/0x650 fs/file_table.c:468
 ____fput+0x1c/0x30 fs/file_table.c:496
 task_work_run+0x131/0x1a0 kernel/task_work.c:227
 resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
 exit_to_user_mode_loop+0xe4/0x100 kernel/entry/common.c:43
 exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline]
 syscall_exit_to_user_mode_work include/linux/entry-common.h:175 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:210 [inline]
 do_syscall_64+0x1d6/0x200 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff8881167621d8 of 8 bytes by task 16676 on cpu 0:
 memcmp lib/string.c:683 [inline]
 bcmp+0x23/0x90 lib/string.c:715
 memcmp include/linux/fortify-string.h:727 [inline]
 __bpf_get_stackid+0x371/0x800 kernel/bpf/stackmap.c:279
 ____bpf_get_stackid kernel/bpf/stackmap.c:324 [inline]
 bpf_get_stackid+0xee/0x120 kernel/bpf/stackmap.c:300
 ____bpf_get_stackid_raw_tp kernel/trace/bpf_trace.c:1810 [inline]
 bpf_get_stackid_raw_tp+0xf6/0x120 kernel/trace/bpf_trace.c:1799
 bpf_prog_e6fc920cfeff8120+0x2a/0x32
 bpf_dispatcher_nop_func include/linux/bpf.h:1332 [inline]
 __bpf_prog_run include/linux/filter.h:718 [inline]
 bpf_prog_run include/linux/filter.h:725 [inline]
 __bpf_trace_run kernel/trace/bpf_trace.c:2257 [inline]
 bpf_trace_run2+0x107/0x1c0 kernel/trace/bpf_trace.c:2298
 __traceiter_kfree+0x2e/0x50 include/trace/events/kmem.h:94
 __do_trace_kfree include/trace/events/kmem.h:94 [inline]
 trace_kfree include/trace/events/kmem.h:94 [inline]
 kfree+0x27b/0x320 mm/slub.c:4866
 ___sys_recvmsg+0x135/0x370 net/socket.c:2877
 do_recvmmsg+0x1ef/0x540 net/socket.c:2971
 __sys_recvmmsg net/socket.c:3045 [inline]
 __do_sys_recvmmsg net/socket.c:3068 [inline]
 __se_sys_recvmmsg net/socket.c:3061 [inline]
 __x64_sys_recvmmsg+0xe5/0x170 net/socket.c:3061
 x64_sys_call+0x27a6/0x2ff0 arch/x86/include/generated/asm/syscalls_64.h:300
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0xffffffff8567eeb2 -> 0xffffffff81933728

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 16676 Comm: syz.8.14353 Tainted: G        W           syzkaller #0 PREEMPT(voluntary) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
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