Re: [PATCH] net: qrtr: fix another OOB Read in qrtr_endpoint_post

Yes, this bug can be triggered without your change. The reason why I
point to your commit is to make it easier for everyone to understand
this bug.

Regards,
 Xiaolong Huang (butt3rflyh4ck)

On Fri, Aug 20, 2021 at 3:53 AM Pavel Skripkin [off-list ref] wrote:

On 8/19/21 10:16 PM, Jakub Kicinski wrote:

quoted

On Fri, 20 Aug 2021 02:14:58 +0800 butt3rflyh4ck wrote:

quoted

From: butt3rflyh4ck <redacted>

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.

quoted

Signed-off-by: butt3rflyh4ck <redacted>

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).

quoted

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 <redacted>




With regards,
Pavel Skripkin

-- 
Active Defense Lab of Venustech