CVE-2023-52521 Information

Description

In the Linux kernel the following vulnerability has been resolved:

bpf: Annotate bpf_long_memcpy with data_race

syzbot reported a data race splat between two processes trying to update the same BPF map value via syscall on different CPUs:

BUG: KCSAN: data-race in bpf_percpu_array_update / bpf_percpu_array_update

write to 0xffffe8fffe7425d8 of 8 bytes by task 8257 on cpu 1: bpf_long_memcpy include/linux/bpf.h:428 [inline] bpf_obj_memcpy include/linux/bpf.h:441 [inline] copy_map_value_long include/linux/bpf.h:464 [inline] bpf_percpu_array_update+0x3bb/0x500 kernel/bpf/arraymap.c:380 bpf_map_update_value+0x190/0x370 kernel/bpf/syscall.c:175 generic_map_update_batch+0x3ae/0x4f0 kernel/bpf/syscall.c:1749 bpf_map_do_batch+0x2df/0x3d0 kernel/bpf/syscall.c:4648 __sys_bpf+0x28a/0x780 __do_sys_bpf kernel/bpf/syscall.c:5241 [inline] __se_sys_bpf kernel/bpf/syscall.c:5239 [inline] __x64_sys_bpf+0x43/0x50 kernel/bpf/syscall.c:5239 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x63/0xcd

write to 0xffffe8fffe7425d8 of 8 bytes by task 8268 on cpu 0: bpf_long_memcpy include/linux/bpf.h:428 [inline] bpf_obj_memcpy include/linux/bpf.h:441 [inline] copy_map_value_long include/linux/bpf.h:464 [inline] bpf_percpu_array_update+0x3bb/0x500 kernel/bpf/arraymap.c:380 bpf_map_update_value+0x190/0x370 kernel/bpf/syscall.c:175 generic_map_update_batch+0x3ae/0x4f0 kernel/bpf/syscall.c:1749 bpf_map_do_batch+0x2df/0x3d0 kernel/bpf/syscall.c:4648 __sys_bpf+0x28a/0x780 __do_sys_bpf kernel/bpf/syscall.c:5241 [inline] __se_sys_bpf kernel/bpf/syscall.c:5239 [inline] __x64_sys_bpf+0x43/0x50 kernel/bpf/syscall.c:5239 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x63/0xcd

value changed: 0x0000000000000000 -> 0xfffffff000002788

The bpf_long_memcpy is used with 8-byte aligned pointers power-of-8 size and forced to use long read/writes to try to atomically copy long counters. It is best-effort only and no barriers are here since it will race with concurrent updates from BPF programs. The bpf_long_memcpy() is called from bpf(2) syscall. Marco suggested that the best way to make this known to KCSAN would be to use data_race() annotation.

Reference

https://git.kernel.org/stable/c/5685f8a6fae1fbe480493b980a1fdbe67c86a094 https://git.kernel.org/stable/c/e562de67dc9196f2415f117796a2108c00ac7fc6 https://git.kernel.org/stable/c/6a86b5b5cd76d2734304a0173f5f01aa8aa2025e