net: filter: fix possible use after free

net: filter: fix possible use after free

[ No appicable upstream commit, this bug has been subsequently been
  fixed as a side effect of other changes. ]

If kmemdup() fails, we free fp->orig_prog and return -ENOMEM

sk_attach_filter()
 -> sk_filter_uncharge(sk, fp)
  -> sk_filter_release(fp)
   -> call_rcu(&fp->rcu, sk_filter_release_rcu)
    -> sk_filter_release_rcu()
     -> sk_release_orig_filter()
        fprog = fp->orig_prog; // not NULL, but points to freed memory
	  kfree(fprog->filter); // use after free, potential corruption
          kfree(fprog); // double free or corruption

Note: This was fixed in 3.17+ with commit 278571baca2a
("net: filter: simplify socket charging")

Found by AddressSanitizer

Signed-off-by: Eric Dumazet <edumazet@google.com>
Fixes: a3ea269b8bcdb ("net: filter: keep original BPF program around")
Acked-by: Alexei Starovoitov <ast@plumgrid.com>
Acked-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>