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| author | Jiayuan Chen <jiayuan.chen@linux.dev> | 2025-12-23 13:14:12 +0800 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2026-01-08 10:16:49 +0100 |
| commit | 787515ccb2292f82eb0876993129154629a49651 (patch) | |
| tree | 34689176a9555faaafe50546d162f23d8361688b /net/ipv6 | |
| parent | 92d900aac3a5721fb54f3328f1e089b44a861c38 (diff) | |
| download | linux-787515ccb2292f82eb0876993129154629a49651.tar.gz linux-787515ccb2292f82eb0876993129154629a49651.tar.bz2 linux-787515ccb2292f82eb0876993129154629a49651.zip | |
ipv6: fix a BUG in rt6_get_pcpu_route() under PREEMPT_RT
[ Upstream commit 1adaea51c61b52e24e7ab38f7d3eba023b2d050d ]
On PREEMPT_RT kernels, after rt6_get_pcpu_route() returns NULL, the
current task can be preempted. Another task running on the same CPU
may then execute rt6_make_pcpu_route() and successfully install a
pcpu_rt entry. When the first task resumes execution, its cmpxchg()
in rt6_make_pcpu_route() will fail because rt6i_pcpu is no longer
NULL, triggering the BUG_ON(prev). It's easy to reproduce it by adding
mdelay() after rt6_get_pcpu_route().
Using preempt_disable/enable is not appropriate here because
ip6_rt_pcpu_alloc() may sleep.
Fix this by handling the cmpxchg() failure gracefully on PREEMPT_RT:
free our allocation and return the existing pcpu_rt installed by
another task. The BUG_ON is replaced by WARN_ON_ONCE for non-PREEMPT_RT
kernels where such races should not occur.
Link: https://syzkaller.appspot.com/bug?extid=9b35e9bc0951140d13e6
Fixes: d2d6422f8bd1 ("x86: Allow to enable PREEMPT_RT.")
Reported-by: syzbot+9b35e9bc0951140d13e6@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/6918cd88.050a0220.1c914e.0045.GAE@google.com/T/
Signed-off-by: Jiayuan Chen <jiayuan.chen@linux.dev>
Link: https://patch.msgid.link/20251223051413.124687-1-jiayuan.chen@linux.dev
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Diffstat (limited to 'net/ipv6')
| -rw-r--r-- | net/ipv6/route.c | 13 |
1 files changed, 12 insertions, 1 deletions
diff --git a/net/ipv6/route.c b/net/ipv6/route.c index aee6a10b112a..a3e051dc66ee 100644 --- a/net/ipv6/route.c +++ b/net/ipv6/route.c @@ -1470,7 +1470,18 @@ static struct rt6_info *rt6_make_pcpu_route(struct net *net, p = this_cpu_ptr(res->nh->rt6i_pcpu); prev = cmpxchg(p, NULL, pcpu_rt); - BUG_ON(prev); + if (unlikely(prev)) { + /* + * Another task on this CPU already installed a pcpu_rt. + * This can happen on PREEMPT_RT where preemption is possible. + * Free our allocation and return the existing one. + */ + WARN_ON_ONCE(!IS_ENABLED(CONFIG_PREEMPT_RT)); + + dst_dev_put(&pcpu_rt->dst); + dst_release(&pcpu_rt->dst); + return prev; + } if (res->f6i->fib6_destroying) { struct fib6_info *from; |