x_tables: ip6_tables: rpfilter match: used from hooks OUTPUT, but only valid from PREROUTING
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BUG: KCSAN: data-race in _prb_read_valid / data_alloc

write to 0xffffffff8686b1c8 of 8 bytes by task 4931 on cpu 1:
 data_alloc+0x310/0x390 kernel/printk/printk_ringbuffer.c:1129
 prb_reserve+0x8d7/0xad0 kernel/printk/printk_ringbuffer.c:1724
 vprintk_store+0x53c/0x830 kernel/printk/printk.c:2302
 vprintk_emit+0x15a/0x5c0 kernel/printk/printk.c:2402
 vprintk_default+0x26/0x30 kernel/printk/printk.c:2441
 vprintk+0x1d/0x30 kernel/printk/printk_safe.c:82
 _printk+0x79/0xa0 kernel/printk/printk.c:2451
 __netdev_printk+0x310/0x370 net/core/dev.c:12911
 netdev_info+0x9b/0xd0 net/core/dev.c:12958
 slcan_close+0xb8/0xe0 drivers/net/can/slcan/slcan-core.c:893
 tty_ldisc_close+0x74/0xa0 drivers/tty/tty_ldisc.c:455
 tty_set_ldisc+0x1b9/0x380 drivers/tty/tty_ldisc.c:557
 tiocsetd+0x51/0x60 drivers/tty/tty_io.c:2429
 tty_ioctl+0xa79/0xb80 drivers/tty/tty_io.c:2728
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xce/0x140 fs/ioctl.c:583
 __x64_sys_ioctl+0x43/0x50 fs/ioctl.c:583
 x64_sys_call+0x14b0/0x3000 arch/x86/include/generated/asm/syscalls_64.h:17
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xca/0x2b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffffff8686b1c8 of 16 bytes by task 4934 on cpu 0:
 desc_read kernel/printk/printk_ringbuffer.c:496 [inline]
 desc_read_finalized_seq kernel/printk/printk_ringbuffer.c:1931 [inline]
 prb_read kernel/printk/printk_ringbuffer.c:1979 [inline]
 _prb_read_valid+0x1bc/0x920 kernel/printk/printk_ringbuffer.c:2170
 prb_read_valid+0x3c/0x60 kernel/printk/printk_ringbuffer.c:2242
 printk_get_next_message+0xc8/0x510 kernel/printk/printk.c:2999
 console_emit_next_record kernel/printk/printk.c:3083 [inline]
 console_flush_one_record kernel/printk/printk.c:3215 [inline]
 console_flush_all+0x2c8/0x6c0 kernel/printk/printk.c:3289
 __console_flush_and_unlock kernel/printk/printk.c:3319 [inline]
 console_unlock+0x97/0x270 kernel/printk/printk.c:3359
 vprintk_emit+0x39f/0x5c0 kernel/printk/printk.c:2426
 vprintk_default+0x26/0x30 kernel/printk/printk.c:2441
 vprintk+0x1d/0x30 kernel/printk/printk_safe.c:82
 _printk+0x79/0xa0 kernel/printk/printk.c:2451
 xt_check_match+0x487/0x4f0 net/netfilter/x_tables.c:-1
 check_match net/ipv6/netfilter/ip6_tables.c:488 [inline]
 find_check_match net/ipv6/netfilter/ip6_tables.c:505 [inline]
 find_check_entry net/ipv6/netfilter/ip6_tables.c:556 [inline]
 translate_table+0xb4b/0x1070 net/ipv6/netfilter/ip6_tables.c:733
 do_replace net/ipv6/netfilter/ip6_tables.c:1154 [inline]
 do_ip6t_set_ctl+0x678/0x840 net/ipv6/netfilter/ip6_tables.c:1644
 nf_setsockopt+0x199/0x1b0 net/netfilter/nf_sockopt.c:101
 ipv6_setsockopt+0x11a/0x130 net/ipv6/ipv6_sockglue.c:978
 tcp_setsockopt+0x98/0xb0 net/ipv4/tcp.c:4164
 sock_common_setsockopt+0x69/0x80 net/core/sock.c:3973
 do_sock_setsockopt net/socket.c:2322 [inline]
 __sys_setsockopt+0x184/0x200 net/socket.c:2347
 __do_sys_setsockopt net/socket.c:2353 [inline]
 __se_sys_setsockopt net/socket.c:2350 [inline]
 __x64_sys_setsockopt+0x64/0x80 net/socket.c:2350
 x64_sys_call+0x21d5/0x3000 arch/x86/include/generated/asm/syscalls_64.h:55
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xca/0x2b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 4934 Comm: syz.4.11216 Not tainted syzkaller #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
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