netdev - Re: [PATCH net] ipmr: fix error path when mr_table

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Message-Id: <20180604.172514.1940145189918116408.davem@davemloft.net>
Date:   Mon, 04 Jun 2018 17:25:14 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     sd@...asysnail.net
Cc:     netdev@...r.kernel.org, edumazet@...gle.com,
        nikolay@...ulusnetworks.com, yuvalm@...lanox.com,
        ivecera@...hat.com
Subject: Re: [PATCH net] ipmr: fix error path when mr_table_alloc fails

From: Sabrina Dubroca <sd@...asysnail.net>
Date: Mon,  4 Jun 2018 13:55:54 +0200

> commit 0bbbf0e7d0e7 ("ipmr, ip6mr: Unite creation of new mr_table")
> refactored ipmr_new_table, so that it now returns NULL when
> mr_table_alloc fails. Unfortunately, all callers of ipmr_new_table
> expect an ERR_PTR. commit 66fb33254f45 ("ipmr: properly check
> rhltable_init() return value") followed suit.
> 
> This can result in NULL deref, when ipmr_rules_exit calls
> ipmr_free_table with NULL net->ipv4.mrt in the
> !CONFIG_IP_MROUTE_MULTIPLE_TABLES version.
> 
> This patch makes mr_table_alloc return errors, and changes
> ip6mr_new_table and its callers to return/expect error pointers as
> well. It also removes the version of mr_table_alloc defined under
> !CONFIG_IP_MROUTE_COMMON, since it is never used.
> 
> Fixes: 0bbbf0e7d0e7 ("ipmr, ip6mr: Unite creation of new mr_table")
> Fixes: 66fb33254f45 ("ipmr: properly check rhltable_init() return value")
> Signed-off-by: Sabrina Dubroca <sd@...asysnail.net>

This adds a new warning with gcc-8.1.1 on Fedora 28

  CC [M]  net/ipv6/ip6mr.o
In file included from ./arch/x86/include/asm/current.h:5,
                 from ./include/linux/sched.h:12,
                 from ./include/linux/uaccess.h:5,
                 from net/ipv6/ip6mr.c:19:
net/ipv6/ip6mr.c: In function ‘ip6_mroute_setsockopt’:
./include/linux/compiler.h:177:26: warning: ‘mrt’ may be used uninitialized in this function [-Wmaybe-uninitialized]
  case 8: *(__u64 *)res = *(volatile __u64 *)p; break;  \
                          ^
net/ipv6/ip6mr.c:1752:20: note: ‘mrt’ was declared here
   struct mr_table *mrt;
                    ^~~