Re: [GIT] Networking

From	Sowmini Varadhan <sowmini.varadhan@oracle.com>
Newsgroups	linux.kernel
Subject	Re: [GIT] Networking
Date	2017-07-10 14:20 +0200
Message-ID	<u1FPs-4Ta-27@gated-at.bofh.it> (permalink)
References	<u0VjA-11F-9@gated-at.bofh.it> <u1pAZ-2UI-15@gated-at.bofh.it> <u1pUm-3gg-3@gated-at.bofh.it> <u1rjr-43b-3@gated-at.bofh.it> <u1DNF-3IW-11@gated-at.bofh.it>
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On (07/10/17 18:05), Herbert Xu wrote:
> 
> Hmm, I can't see the problem in af_alg_accept.  The struct socket
> comes directly from sys_accept() which creates it using sock_alloc.
> 
> So the only thing I can think of is that the memory returned by
> sock_alloc is not zeroed and therefore the WARN_ON is just reading
> garbage.

Then it is odd that this WARN_ON is not triggered for other sockets
(e.g., for TCP sockets), though it happens easily with AF_ALG. 

But it's not sock_alloc() - that function is returning a properly
zeroed ->sk.

The reason that the WARN_ON is triggered is that af_alg_accept() calls
sock_init_data() which does 

   2636         if (sock) {
    :
   2639                 sock->sk        =       sk;

So we can do one of the following:

1. drop the WARN_ON(), which makes true leaks hard to detect
2. change the WARN_ON() to WARN_ON(parent->sk && parent->sk != sk)

#2 assumes that all the refcount book-keeping is being done
correctly (there is the danger that we end up taking 2 refs on the sk) 

--Sowmini

Thread

[GIT] Networking David Miller <davem@davemloft.net> - 2017-07-08 12:40 +0200
  Re: [GIT] Networking Linus Torvalds <torvalds@linux-foundation.org> - 2017-07-09 21:00 +0200
    Re: [GIT] Networking Sowmini Varadhan <sowmini.varadhan@oracle.com> - 2017-07-09 21:20 +0200
      Re: [GIT] Networking David Miller <davem@davemloft.net> - 2017-07-09 22:50 +0200
        Re: [GIT] Networking Herbert Xu <herbert@gondor.apana.org.au> - 2017-07-10 12:10 +0200
          Re: [GIT] Networking Sowmini Varadhan <sowmini.varadhan@oracle.com> - 2017-07-10 14:20 +0200
            Re: [GIT] Networking Herbert Xu <herbert@gondor.apana.org.au> - 2017-07-10 16:10 +0200
              Re: [GIT] Networking David Miller <davem@davemloft.net> - 2017-07-11 22:40 +0200
                Re: [GIT] Networking Herbert Xu <herbert@gondor.apana.org.au> - 2017-07-12 03:50 +0200

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