This is a note to let you know that I've just added the patch titled
nexthop: Fix division by zero while replacing a resilient group
to the 5.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
nexthop-fix-division-by-zero-while-replacing-a-resilient-group.patch
and it can be found in the queue-5.14 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 563f23b002534176f49524b5ca0e1d94d8906c40 Mon Sep 17 00:00:00 2001
From: Ido Schimmel <idosch@xxxxxxxxxx>
Date: Fri, 17 Sep 2021 16:02:18 +0300
Subject: nexthop: Fix division by zero while replacing a resilient group
From: Ido Schimmel <idosch@xxxxxxxxxx>
commit 563f23b002534176f49524b5ca0e1d94d8906c40 upstream.
The resilient nexthop group torture tests in fib_nexthop.sh exposed a
possible division by zero while replacing a resilient group [1]. The
division by zero occurs when the data path sees a resilient nexthop
group with zero buckets.
The tests replace a resilient nexthop group in a loop while traffic is
forwarded through it. The tests do not specify the number of buckets
while performing the replacement, resulting in the kernel allocating a
stub resilient table (i.e, 'struct nh_res_table') with zero buckets.
This table should never be visible to the data path, but the old nexthop
group (i.e., 'oldg') might still be used by the data path when the stub
table is assigned to it.
Fix this by only assigning the stub table to the old nexthop group after
making sure the group is no longer used by the data path.
Tested with fib_nexthops.sh:
Tests passed: 222
Tests failed: 0
[1]
divide error: 0000 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 1850 Comm: ping Not tainted 5.14.0-custom-10271-ga86eb53057fe #1107
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-4.fc34 04/01/2014
RIP: 0010:nexthop_select_path+0x2d2/0x1a80
[...]
Call Trace:
fib_select_multipath+0x79b/0x1530
fib_select_path+0x8fb/0x1c10
ip_route_output_key_hash_rcu+0x1198/0x2da0
ip_route_output_key_hash+0x190/0x340
ip_route_output_flow+0x21/0x120
raw_sendmsg+0x91d/0x2e10
inet_sendmsg+0x9e/0xe0
__sys_sendto+0x23d/0x360
__x64_sys_sendto+0xe1/0x1b0
do_syscall_64+0x35/0x80
entry_SYSCALL_64_after_hwframe+0x44/0xae
Cc: stable@xxxxxxxxxxxxxxx
Fixes: 283a72a5599e ("nexthop: Add implementation of resilient next-hop groups")
Signed-off-by: Ido Schimmel <idosch@xxxxxxxxxx>
Reviewed-by: Petr Machata <petrm@xxxxxxxxxx>
Reviewed-by: David Ahern <dsahern@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
net/ipv4/nexthop.c | 2 ++
1 file changed, 2 insertions(+)
--- a/net/ipv4/nexthop.c
+++ b/net/ipv4/nexthop.c
@@ -1982,6 +1982,8 @@ static int replace_nexthop_grp(struct ne
rcu_assign_pointer(old->nh_grp, newg);
if (newg->resilient) {
+ /* Make sure concurrent readers are not using 'oldg' anymore. */
+ synchronize_net();
rcu_assign_pointer(oldg->res_table, tmp_table);
rcu_assign_pointer(oldg->spare->res_table, tmp_table);
}
Patches currently in stable-queue which might be from idosch@xxxxxxxxxx are
queue-5.14/nexthop-fix-division-by-zero-while-replacing-a-resilient-group.patch
