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    Subject[PATCH 4.20 34/52] ipv6: route: enforce RCU protection in rt6_update_exception_stamp_rt()
    Date
    4.20-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Paolo Abeni <pabeni@redhat.com>

    [ Upstream commit 193f3685d0546b0cea20c99894aadb70098e47bf ]

    We must access rt6_info->from under RCU read lock: move the
    dereference under such lock, with proper annotation.

    v1 -> v2:
    - avoid using multiple, racy, fetch operations for rt->from

    Fixes: a68886a69180 ("net/ipv6: Make from in rt6_info rcu protected")
    Signed-off-by: Paolo Abeni <pabeni@redhat.com>
    Reviewed-by: David Ahern <dsahern@gmail.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    net/ipv6/route.c | 11 ++++++-----
    1 file changed, 6 insertions(+), 5 deletions(-)

    --- a/net/ipv6/route.c
    +++ b/net/ipv6/route.c
    @@ -1608,15 +1608,15 @@ static int rt6_remove_exception_rt(struc
    static void rt6_update_exception_stamp_rt(struct rt6_info *rt)
    {
    struct rt6_exception_bucket *bucket;
    - struct fib6_info *from = rt->from;
    struct in6_addr *src_key = NULL;
    struct rt6_exception *rt6_ex;
    -
    - if (!from ||
    - !(rt->rt6i_flags & RTF_CACHE))
    - return;
    + struct fib6_info *from;

    rcu_read_lock();
    + from = rcu_dereference(rt->from);
    + if (!from || !(rt->rt6i_flags & RTF_CACHE))
    + goto unlock;
    +
    bucket = rcu_dereference(from->rt6i_exception_bucket);

    #ifdef CONFIG_IPV6_SUBTREES
    @@ -1635,6 +1635,7 @@ static void rt6_update_exception_stamp_r
    if (rt6_ex)
    rt6_ex->stamp = jiffies;

    +unlock:
    rcu_read_unlock();
    }


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