Re: [PATCH net] ipv6: fix a dst leak when removing its exception

[David Ahern <dsa@cumulusnetworks.com>]

On 11/14/18 11:03 AM, David Ahern wrote:
> On 11/13/18 8:48 AM, Xin Long wrote:
>> These is no need to hold dst before calling rt6_remove_exception_rt().
>> The call to dst_hold_safe() in ip6_link_failure() was for ip6_del_rt(),
>> which has been removed in Commit 93531c674315 ("net/ipv6: separate
>> handling of FIB entries from dst based routes"). Otherwise, it will
>> cause a dst leak.
>>
>> This patch is to simply remove the dst_hold_safe() call before calling
>> rt6_remove_exception_rt() and also do the same in ip6_del_cached_rt().
>> It's safe, because the removal of the exception that holds its dst's
>> refcnt is protected by rt6_exception_lock.
>>
>> Fixes: 93531c674315 ("net/ipv6: separate handling of FIB entries from dst based routes")
>> Fixes: 23fb93a4d3f1 ("net/ipv6: Cleanup exception and cache route handling")
>> Reported-by: Li Shuang <shuali@redhat.com>
>> Signed-off-by: Xin Long <lucien.xin@gmail.com>
>> ---
>>  net/ipv6/route.c | 7 +++----
>>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> was this problem actually hit or is this patch based on a code analysis?
> 

I ask because I have not been able to reproduce the leak using existing
tests (e.g., pmtu) that I know create exceptions.

If this problem was hit, it would be good to get a test case for it.