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[85.127.190.169]) by smtp.gmail.com with ESMTPSA id k12sm3467494edo.50.2021.04.01.06.01.21 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 01 Apr 2021 06:01:21 -0700 (PDT) Subject: Re: [Drbd-dev] [PATCH] drbd: Fix a use after free in get_initial_state To: Lv Yunlong Cc: philipp.reisner@linbit.com, lars.ellenberg@linbit.com, axboe@kernel.dk, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, drbd-dev@lists.linbit.com References: <20210401115753.3684-1-lyl2019@mail.ustc.edu.cn> From: =?UTF-8?Q?Christoph_B=c3=b6hmwalder?= Message-ID: Date: Thu, 1 Apr 2021 15:01:20 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.0 MIME-Version: 1.0 In-Reply-To: <20210401115753.3684-1-lyl2019@mail.ustc.edu.cn> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 4/1/21 1:57 PM, Lv Yunlong wrote: > In get_initial_state, it calls notify_initial_state_done(skb,..) if > cb->args[5]==1. I see that if genlmsg_put() failed in > notify_initial_state_done(), the skb will be freed by nlmsg_free(skb). > Then get_initial_state will goto out and the freed skb will be used by > return value skb->len. > > My patch lets skb_len = skb->len and return the skb_len to avoid the uaf. > > Fixes: a29728463b254 ("drbd: Backport the "events2" command") > Signed-off-by: Lv Yunlong > --- > drivers/block/drbd/drbd_nl.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/drivers/block/drbd/drbd_nl.c b/drivers/block/drbd/drbd_nl.c > index bf7de4c7b96c..474f84675d0a 100644 > --- a/drivers/block/drbd/drbd_nl.c > +++ b/drivers/block/drbd/drbd_nl.c > @@ -4905,6 +4905,7 @@ static int get_initial_state(struct sk_buff *skb, struct netlink_callback *cb) > struct drbd_state_change *state_change = (struct drbd_state_change *)cb->args[0]; > unsigned int seq = cb->args[2]; > unsigned int n; > + unsigned int skb_len = skb->len; > enum drbd_notification_type flags = 0; > > /* There is no need for taking notification_mutex here: it doesn't > @@ -4915,7 +4916,7 @@ static int get_initial_state(struct sk_buff *skb, struct netlink_callback *cb) > cb->args[5]--; > if (cb->args[5] == 1) { > notify_initial_state_done(skb, seq); > - goto out; > + return skb_len; > } > n = cb->args[4]++; > if (cb->args[4] < cb->args[3]) > Thanks for the patch! I think the problem goes even further: skb can also be freed in the notify_*_state_change -> notify_*_state calls below. Also, at the point where we save skb->len into skb_len, skb is not initialized yet. Maybe it makes more sense to not return a length in the first place here, but an error code instead. -- Christoph Böhmwalder LINBIT | Keeping the Digital World Running DRBD HA — Disaster Recovery — Software defined Storage