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Subject: Re: [PATCH] net: qrtr: fix another OOB Read in qrtr_endpoint_post
To:     Jakub Kicinski <kuba@kernel.org>,
        butt3rflyh4ck <butterflyhuangxx@gmail.com>
Cc:     mani@kernel.org, davem@davemloft.net,
        linux-arm-msm@vger.kernel.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        butt3rflyh4ck <butterflyhhuangxx@gmail.com>,
        bjorn.andersson@linaro.org
References: <20210819181458.623832-1-butterflyhuangxx@gmail.com>
 <20210819121630.1223327f@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
From:   Pavel Skripkin <paskripkin@gmail.com>
Message-ID: <3a5aef93-fafb-5076-4133-690928b8644a@gmail.com>
Date:   Thu, 19 Aug 2021 22:53:43 +0300
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On 8/19/21 10:16 PM, Jakub Kicinski wrote:
> On Fri, 20 Aug 2021 02:14:58 +0800 butt3rflyh4ck wrote:
>> From: butt3rflyh4ck <butterflyhhuangxx@gmail.com>
>> 
>> This check was incomplete, did not consider size is 0:
>> 
>> 	if (len != ALIGN(size, 4) + hdrlen)
>>                     goto err;
>> 
>> if size from qrtr_hdr is 0, the result of ALIGN(size, 4)
>> will be 0, In case of len == hdrlen and size == 0
>> in header this check won't fail and
>> 
>> 	if (cb->type == QRTR_TYPE_NEW_SERVER) {
>>                 /* Remote node endpoint can bridge other distant nodes */
>>                 const struct qrtr_ctrl_pkt *pkt = data + hdrlen;
>> 
>>                 qrtr_node_assign(node, le32_to_cpu(pkt->server.node));
>>         }
>> 
>> will also read out of bound from data, which is hdrlen allocated block.
>> 
>> Fixes: 194ccc88297a ("net: qrtr: Support decoding incoming v2 packets")
>> Fixes: ad9d24c9429e ("net: qrtr: fix OOB Read in qrtr_endpoint_post")
> 
> Please make sure to CC authors of patches which are under Fixes, they
> are usually the best people to review the patch. Adding them now.
> 
>> Signed-off-by: butt3rflyh4ck <butterflyhhuangxx@gmail.com>
> 
> We'll need your name. AFAIU it's because of Developer Certificate of
> Origin. You'll need to resend with this fixed (and please remember the CCs).
> 
>> diff --git a/net/qrtr/qrtr.c b/net/qrtr/qrtr.c
>> index 171b7f3be6ef..0c30908628ba 100644
>> --- a/net/qrtr/qrtr.c
>> +++ b/net/qrtr/qrtr.c
>> @@ -493,7 +493,7 @@ int qrtr_endpoint_post(struct qrtr_endpoint *ep, const void *data, size_t len)
>>  		goto err;
>>  	}
>>  
>> -	if (len != ALIGN(size, 4) + hdrlen)
>> +	if (!size || len != ALIGN(size, 4) + hdrlen)
>>  		goto err;
>>  
>>  	if (cb->dst_port != QRTR_PORT_CTRL && cb->type != QRTR_TYPE_DATA &&
> 

I am able to trigger described bug with this repro:

#define _GNU_SOURCE

#include <endian.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <unistd.h>

uint64_t r[1] = {0xffffffffffffffff};

int main(void)
{
    syscall(__NR_mmap, 0x1ffff000ul, 0x1000ul, 0ul, 0x32ul, -1, 0ul);
    syscall(__NR_mmap, 0x20000000ul, 0x1000000ul, 7ul, 0x32ul, -1, 0ul);
    syscall(__NR_mmap, 0x21000000ul, 0x1000ul, 0ul, 0x32ul, -1, 0ul);
    intptr_t res = 0;
    memcpy((void*)0x20000000, "/dev/qrtr-tun\000", 14);
    res = syscall(__NR_openat, 0xffffffffffffff9cul, 0x20000000ul, 
0x82ul, 0);
    if (res != -1)
      r[0] = res;
    memcpy((void*)0x20000000, 
"\x01\x21\x21\x39\x04\x00\x00\x00\xd6\x2c\xf3\x50"
 
"\x1a\x47\x56\x52\x19\x56\x86\xef\x00\x00\x00\x00"
                              "\xff\xff\xff\x00\xfe\xff\xff\xff", 32);
    syscall(__NR_write, r[0], 0x20000000ul, 0x20ul);
    return 0;
}

( I didn't write it, it's modified syzbot's repro :) )

One thing I am wondering about is why Fixes tag points to my commit? My 
commit didn't introduce any bugs, this bug will happen even _without_ my 
change.

Anyway, LGTM!

Reviewed-by: Pavel Skripkin <paskripkin@gmail.com>


With regards,
Pavel Skripkin