From mboxrd@z Thu Jan 1 00:00:00 1970 From: Anmol Karn Subject: Re: [Linux-kernel-mentees] [PATCH] net: rose: Fix Null pointer dereference in rose_send_frame() Date: Thu, 15 Oct 2020 19:40:12 +0530 Message-ID: <20201015141012.GB77038@Thinkpad> References: <20201015001712.72976-1-anmol.karan123@gmail.com> <20201015051225.GA404970@kroah.com> Mime-Version: 1.0 Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=aT/El/Gn9neHvZZa/+9NtdmwjsbnakBhZHDByWNqGyw=; b=BNSxMPGkXPupxt3UFTpBo9CCOJOAFIXlAE7ATUBEzeF+Q3f5qZWm3G/Nv3rNGX5D8+ ZhH59Q/TWJX8QmM1PClQq4PU5tS9hticmSRCwXGyL7W50NiK1K9X1otuXEIIlVIS1KUP c7V8gmqtIgMMZJugVmA9+PpgAtU3iW9UUaXDx59USDLehgNO1+hyNHtEKXhhdRavDWHB LttvXd8TkTod160mb24X6WoGKqOB1vflsdcROKt5r7sY1/BgfADkLG7KgAcapfgpJc8V ke+SdeS7bPizwOMnfQz16w8LTPHMzpsPOj97IXJD2EWzGygCvDL6INqqysepHGsgOhfD zPGQ== Content-Disposition: inline In-Reply-To: <20201015051225.GA404970@kroah.com> List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Greg KH Cc: ralf@linux-mips.org, davem@davemloft.net, kuba@kernel.org, netdev@vger.kernel.org, syzkaller-bugs@googlegroups.com, linux-kernel@vger.kernel.org, syzbot+a1c743815982d9496393@syzkaller.appspotmail.com, linux-hams@vger.kernel.org, linux-kernel-mentees@lists.linuxfoundation.org On Thu, Oct 15, 2020 at 07:12:25AM +0200, Greg KH wrote: > On Thu, Oct 15, 2020 at 05:47:12AM +0530, Anmol Karn wrote: > > In rose_send_frame(), when comparing two ax.25 addresses, it assigns rose_call to > > either global ROSE callsign or default port, but when the former block triggers and > > rose_call is assigned by (ax25_address *)neigh->dev->dev_addr, a NULL pointer is > > dereferenced by 'neigh' when dereferencing 'dev'. > > > > - net/rose/rose_link.c > > This bug seems to get triggered in this line: > > > > rose_call = (ax25_address *)neigh->dev->dev_addr; > > > > Prevent it by checking NULL condition for neigh->dev before comparing addressed for > > rose_call initialization. > > > > Reported-by: syzbot+a1c743815982d9496393@syzkaller.appspotmail.com > > Link: https://syzkaller.appspot.com/bug?id=9d2a7ca8c7f2e4b682c97578dfa3f236258300b3 > > Signed-off-by: Anmol Karn > > --- > > I am bit sceptical about the error return code, please suggest if anything else is > > appropriate in place of '-ENODEV'. > > > > net/rose/rose_link.c | 3 +++ > > 1 file changed, 3 insertions(+) > > > > diff --git a/net/rose/rose_link.c b/net/rose/rose_link.c > > index f6102e6f5161..92ea6a31d575 100644 > > --- a/net/rose/rose_link.c > > +++ b/net/rose/rose_link.c > > @@ -97,6 +97,9 @@ static int rose_send_frame(struct sk_buff *skb, struct rose_neigh *neigh) > > ax25_address *rose_call; > > ax25_cb *ax25s; > > > > + if (!neigh->dev) > > + return -ENODEV; > > How can ->dev not be set at this point in time? Shouldn't that be > fixed, because it could change right after you check this, right? > > thanks, > > greg k-h Hello Sir, Thanks for the review, After following the call trace i thought, if neigh->dev is NULL it should be checked, but I will figure out what is going on with the crash reproducer, and I think rose_loopback_timer() is the place where problem started. Also, I have created a diff for checking neigh->dev before assigning ROSE callsign , please give your suggestions on this. diff --git a/net/rose/rose_link.c b/net/rose/rose_link.c index f6102e6f5161..2ddd5e559442 100644 --- a/net/rose/rose_link.c +++ b/net/rose/rose_link.c @@ -97,10 +97,14 @@ static int rose_send_frame(struct sk_buff *skb, struct rose_neigh *neigh) ax25_address *rose_call; ax25_cb *ax25s; - if (ax25cmp(&rose_callsign, &null_ax25_address) == 0) - rose_call = (ax25_address *)neigh->dev->dev_addr; - else - rose_call = &rose_callsign; + if (neigh->dev) { + if (ax25cmp(&rose_callsign, &null_ax25_address) == 0) + rose_call = (ax25_address *)neigh->dev->dev_addr; + else + rose_call = &rose_callsign; + } else { + return -ENODEV; + } ax25s = neigh->ax25; neigh->ax25 = ax25_send_frame(skb, 260, rose_call, &neigh->callsign, neigh->digipeat, neigh->dev); Thanks, Anmol From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.3 required=3.0 tests=BAYES_00,DKIM_ADSP_CUSTOM_MED, DKIM_INVALID,DKIM_SIGNED,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3D79BC43457 for ; 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Thu, 15 Oct 2020 07:10:21 -0700 (PDT) Received: from Thinkpad ([45.118.167.207]) by smtp.gmail.com with ESMTPSA id b185sm3341294pgc.68.2020.10.15.07.10.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 15 Oct 2020 07:10:20 -0700 (PDT) Date: Thu, 15 Oct 2020 19:40:12 +0530 From: Anmol Karn To: Greg KH Message-ID: <20201015141012.GB77038@Thinkpad> References: <20201015001712.72976-1-anmol.karan123@gmail.com> <20201015051225.GA404970@kroah.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20201015051225.GA404970@kroah.com> Cc: netdev@vger.kernel.org, syzkaller-bugs@googlegroups.com, linux-kernel@vger.kernel.org, ralf@linux-mips.org, syzbot+a1c743815982d9496393@syzkaller.appspotmail.com, linux-hams@vger.kernel.org, kuba@kernel.org, linux-kernel-mentees@lists.linuxfoundation.org, davem@davemloft.net Subject: Re: [Linux-kernel-mentees] [PATCH] net: rose: Fix Null pointer dereference in rose_send_frame() X-BeenThere: linux-kernel-mentees@lists.linuxfoundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: linux-kernel-mentees-bounces@lists.linuxfoundation.org Sender: "Linux-kernel-mentees" On Thu, Oct 15, 2020 at 07:12:25AM +0200, Greg KH wrote: > On Thu, Oct 15, 2020 at 05:47:12AM +0530, Anmol Karn wrote: > > In rose_send_frame(), when comparing two ax.25 addresses, it assigns rose_call to > > either global ROSE callsign or default port, but when the former block triggers and > > rose_call is assigned by (ax25_address *)neigh->dev->dev_addr, a NULL pointer is > > dereferenced by 'neigh' when dereferencing 'dev'. > > > > - net/rose/rose_link.c > > This bug seems to get triggered in this line: > > > > rose_call = (ax25_address *)neigh->dev->dev_addr; > > > > Prevent it by checking NULL condition for neigh->dev before comparing addressed for > > rose_call initialization. > > > > Reported-by: syzbot+a1c743815982d9496393@syzkaller.appspotmail.com > > Link: https://syzkaller.appspot.com/bug?id=9d2a7ca8c7f2e4b682c97578dfa3f236258300b3 > > Signed-off-by: Anmol Karn > > --- > > I am bit sceptical about the error return code, please suggest if anything else is > > appropriate in place of '-ENODEV'. > > > > net/rose/rose_link.c | 3 +++ > > 1 file changed, 3 insertions(+) > > > > diff --git a/net/rose/rose_link.c b/net/rose/rose_link.c > > index f6102e6f5161..92ea6a31d575 100644 > > --- a/net/rose/rose_link.c > > +++ b/net/rose/rose_link.c > > @@ -97,6 +97,9 @@ static int rose_send_frame(struct sk_buff *skb, struct rose_neigh *neigh) > > ax25_address *rose_call; > > ax25_cb *ax25s; > > > > + if (!neigh->dev) > > + return -ENODEV; > > How can ->dev not be set at this point in time? Shouldn't that be > fixed, because it could change right after you check this, right? > > thanks, > > greg k-h Hello Sir, Thanks for the review, After following the call trace i thought, if neigh->dev is NULL it should be checked, but I will figure out what is going on with the crash reproducer, and I think rose_loopback_timer() is the place where problem started. Also, I have created a diff for checking neigh->dev before assigning ROSE callsign , please give your suggestions on this. diff --git a/net/rose/rose_link.c b/net/rose/rose_link.c index f6102e6f5161..2ddd5e559442 100644 --- a/net/rose/rose_link.c +++ b/net/rose/rose_link.c @@ -97,10 +97,14 @@ static int rose_send_frame(struct sk_buff *skb, struct rose_neigh *neigh) ax25_address *rose_call; ax25_cb *ax25s; - if (ax25cmp(&rose_callsign, &null_ax25_address) == 0) - rose_call = (ax25_address *)neigh->dev->dev_addr; - else - rose_call = &rose_callsign; + if (neigh->dev) { + if (ax25cmp(&rose_callsign, &null_ax25_address) == 0) + rose_call = (ax25_address *)neigh->dev->dev_addr; + else + rose_call = &rose_callsign; + } else { + return -ENODEV; + } ax25s = neigh->ax25; neigh->ax25 = ax25_send_frame(skb, 260, rose_call, &neigh->callsign, neigh->digipeat, neigh->dev); Thanks, Anmol _______________________________________________ Linux-kernel-mentees mailing list Linux-kernel-mentees@lists.linuxfoundation.org https://lists.linuxfoundation.org/mailman/listinfo/linux-kernel-mentees