1bef4c223b
While looking at a syzbot KCSAN report [1], I found multiple issues in this code : 1) fib6_nh->last_probe has an initial value of 0. While probably okay on 64bit kernels, this causes an issue on 32bit kernels since the time_after(jiffies, 0 + interval) might be false ~24 days after boot (for HZ=1000) 2) The data-race found by KCSAN I could use READ_ONCE() and WRITE_ONCE(), but we also can take the opportunity of not piling-up too many rt6_probe_deferred() works by using instead cmpxchg() so that only one cpu wins the race. [1] BUG: KCSAN: data-race in find_match / find_match write to 0xffff8880bb7aabe8 of 8 bytes by interrupt on cpu 1: rt6_probe net/ipv6/route.c:663 [inline] find_match net/ipv6/route.c:757 [inline] find_match+0x5bd/0x790 net/ipv6/route.c:733 __find_rr_leaf+0xe3/0x780 net/ipv6/route.c:831 find_rr_leaf net/ipv6/route.c:852 [inline] rt6_select net/ipv6/route.c:896 [inline] fib6_table_lookup+0x383/0x650 net/ipv6/route.c:2164 ip6_pol_route+0xee/0x5c0 net/ipv6/route.c:2200 ip6_pol_route_output+0x48/0x60 net/ipv6/route.c:2452 fib6_rule_lookup+0x3d6/0x470 net/ipv6/fib6_rules.c:117 ip6_route_output_flags_noref+0x16b/0x230 net/ipv6/route.c:2484 ip6_route_output_flags+0x50/0x1a0 net/ipv6/route.c:2497 ip6_dst_lookup_tail+0x25d/0xc30 net/ipv6/ip6_output.c:1049 ip6_dst_lookup_flow+0x68/0x120 net/ipv6/ip6_output.c:1150 inet6_csk_route_socket+0x2f7/0x420 net/ipv6/inet6_connection_sock.c:106 inet6_csk_xmit+0x91/0x1f0 net/ipv6/inet6_connection_sock.c:121 __tcp_transmit_skb+0xe81/0x1d60 net/ipv4/tcp_output.c:1169 tcp_transmit_skb net/ipv4/tcp_output.c:1185 [inline] tcp_xmit_probe_skb+0x19b/0x1d0 net/ipv4/tcp_output.c:3735 read to 0xffff8880bb7aabe8 of 8 bytes by interrupt on cpu 0: rt6_probe net/ipv6/route.c:657 [inline] find_match net/ipv6/route.c:757 [inline] find_match+0x521/0x790 net/ipv6/route.c:733 __find_rr_leaf+0xe3/0x780 net/ipv6/route.c:831 find_rr_leaf net/ipv6/route.c:852 [inline] rt6_select net/ipv6/route.c:896 [inline] fib6_table_lookup+0x383/0x650 net/ipv6/route.c:2164 ip6_pol_route+0xee/0x5c0 net/ipv6/route.c:2200 ip6_pol_route_output+0x48/0x60 net/ipv6/route.c:2452 fib6_rule_lookup+0x3d6/0x470 net/ipv6/fib6_rules.c:117 ip6_route_output_flags_noref+0x16b/0x230 net/ipv6/route.c:2484 ip6_route_output_flags+0x50/0x1a0 net/ipv6/route.c:2497 ip6_dst_lookup_tail+0x25d/0xc30 net/ipv6/ip6_output.c:1049 ip6_dst_lookup_flow+0x68/0x120 net/ipv6/ip6_output.c:1150 inet6_csk_route_socket+0x2f7/0x420 net/ipv6/inet6_connection_sock.c:106 inet6_csk_xmit+0x91/0x1f0 net/ipv6/inet6_connection_sock.c:121 __tcp_transmit_skb+0xe81/0x1d60 net/ipv4/tcp_output.c:1169 Reported by Kernel Concurrency Sanitizer on: CPU: 0 PID: 18894 Comm: udevd Not tainted 5.4.0-rc3+ #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Fixes: cc3a86c802f0 ("ipv6: Change rt6_probe to take a fib6_nh") Fixes: f547fac624be ("ipv6: rate-limit probes for neighbourless routes") Signed-off-by: Eric Dumazet <edumazet@google.com> Reported-by: syzbot <syzkaller@googlegroups.com> Reviewed-by: David Ahern <dsahern@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.