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[85.163.43.2]) by smtp.gmail.com with ESMTPSA id p15sm6257061wma.40.2020.02.14.00.33.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 14 Feb 2020 00:33:30 -0800 (PST) Date: Fri, 14 Feb 2020 09:33:29 +0100 From: Jiri Pirko To: Eric Dumazet Cc: Eric Dumazet , "David S . Miller" , netdev , Jiri Pirko , syzbot Subject: Re: [PATCH net] net: rtnetlink: fix bugs in rtnl_alt_ifname() Message-ID: <20200214083329.GA2100@nanopsycho> References: <20200213045826.181478-1-edumazet@google.com> <20200213064532.GD22610@nanopsycho> <2e122d94-89a1-f2aa-2613-2fc75ff6b4d1@gmail.com> <741c1c4e-9f83-d5bd-0100-d33cb5db7cc6@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <741c1c4e-9f83-d5bd-0100-d33cb5db7cc6@gmail.com> Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Fri, Feb 14, 2020 at 08:11:26AM CET, eric.dumazet@gmail.com wrote: > > >On 2/12/20 10:58 PM, Eric Dumazet wrote: >> >> >> On 2/12/20 10:45 PM, Jiri Pirko wrote: >>> Thu, Feb 13, 2020 at 05:58:26AM CET, edumazet@google.com wrote: >>>> Since IFLA_ALT_IFNAME is an NLA_STRING, we have no >>>> guarantee it is nul terminated. >>>> >>>> We should use nla_strdup() instead of kstrdup(), since this >>>> helper will make sure not accessing out-of-bounds data. >>>> >>>> >>>> Fixes: 36fbf1e52bd3 ("net: rtnetlink: add linkprop commands to add and delete alternative ifnames") >>>> Signed-off-by: Eric Dumazet >>>> Cc: Jiri Pirko >>>> Reported-by: syzbot >>>> --- >>>> net/core/rtnetlink.c | 26 ++++++++++++-------------- >>>> 1 file changed, 12 insertions(+), 14 deletions(-) >>>> >>>> diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c >>>> index 09c44bf2e1d28842d77b4ed442ef2c051a25ad21..e1152f4ffe33efb0a69f17a1f5940baa04942e5b 100644 >>>> --- a/net/core/rtnetlink.c >>>> +++ b/net/core/rtnetlink.c >>>> @@ -3504,27 +3504,25 @@ static int rtnl_alt_ifname(int cmd, struct net_device *dev, struct nlattr *attr, >>>> if (err) >>>> return err; >>>> >>>> - alt_ifname = nla_data(attr); >>>> + alt_ifname = nla_strdup(attr, GFP_KERNEL); >>>> + if (!alt_ifname) >>>> + return -ENOMEM; >>>> + >>>> if (cmd == RTM_NEWLINKPROP) { >>>> - alt_ifname = kstrdup(alt_ifname, GFP_KERNEL); >>>> - if (!alt_ifname) >>>> - return -ENOMEM; >>>> err = netdev_name_node_alt_create(dev, alt_ifname); >>>> - if (err) { >>>> - kfree(alt_ifname); >>>> - return err; >>>> - } >>>> + if (!err) >>>> + alt_ifname = NULL; >>>> } else if (cmd == RTM_DELLINKPROP) { >>>> err = netdev_name_node_alt_destroy(dev, alt_ifname); >>>> - if (err) >>>> - return err; >>>> } else { >>> >>> >>>> - WARN_ON(1); >>>> - return 0; >>>> + WARN_ON_ONCE(1); >>>> + err = -EINVAL; >>> >>> These 4 lines do not seem to be related to the rest of the patch. Should >>> it be a separate patch? >> >> Well, we have to kfree(alt_ifname). >> >> Generally speaking I tried to avoid return in the middle of this function. >> >> The WARN_ON(1) is dead code today, making it a WARN_ON_ONCE(1) is simply >> a matter of avoiding syslog floods if this path is ever triggered in the future. > >Also, related to this new fancy code ;) > >Is there anything preventing netdev_name_node_alt_destroy() from destroying the primary >ifname ? > >netdev_name_node_lookup() should be able to find dev->name_node itself ? > >Then we would leave a dangling pointer in dev->name_node, and crash later. > >I am thinking we need this fix : That is correct. We need that. Thanks! > >diff --git a/net/core/dev.c b/net/core/dev.c >index a6316b336128cdb31eea6e80f1a47620abbd0d31..3fa2bc2c30ee1350b5b4b400f0552b9bf2a62697 100644 >--- a/net/core/dev.c >+++ b/net/core/dev.c >@@ -331,6 +331,11 @@ int netdev_name_node_alt_destroy(struct net_device *dev, const char *name) > name_node = netdev_name_node_lookup(net, name); > if (!name_node) > return -ENOENT; >+ >+ /* Do not trust users, ever ! */ >+ if (name_node == dev->name_node || name_node->dev != dev) >+ return -EINVAL; >+ > __netdev_name_node_alt_destroy(name_node); > > return 0;