2020-07-22 16:07:58

by Peilin Ye

Subject: [Linux-kernel-mentees] [PATCH net] AX.25: Prevent out-of-bounds read in ax25_sendmsg()

Checks on `addr_len` and `usax->sax25_ndigis` are insufficient.
ax25_sendmsg() can go out of bounds when `usax->sax25_ndigis` equals to 7
or 8. Fix it.

It is safe to remove `usax->sax25_ndigis > AX25_MAX_DIGIS`, since
`addr_len` is guaranteed to be less than or equal to
`sizeof(struct full_sockaddr_ax25)`

Signed-off-by: Peilin Ye <[email protected]>
---
net/ax25/af_ax25.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/ax25/af_ax25.c b/net/ax25/af_ax25.c
index ef5bf116157a..0862fe49d434 100644
--- a/net/ax25/af_ax25.c
+++ b/net/ax25/af_ax25.c
@@ -1509,7 +1509,8 @@ static int ax25_sendmsg(struct socket *sock, struct msghdr *msg, size_t len)
struct full_sockaddr_ax25 *fsa = (struct full_sockaddr_ax25 *)usax;

/* Valid number of digipeaters ? */
- if (usax->sax25_ndigis < 1 || usax->sax25_ndigis > AX25_MAX_DIGIS) {
+ if (usax->sax25_ndigis < 1 || addr_len < sizeof(struct sockaddr_ax25) +
+ sizeof(ax25_address) * usax->sax25_ndigis) {
err = -EINVAL;
goto out;
}
--
2.25.1

2020-07-23 01:09:57

by David Miller

Subject: Re: [Linux-kernel-mentees] [PATCH net] AX.25: Prevent out-of-bounds read in ax25_sendmsg()

From: Peilin Ye <[email protected]>
Date: Wed, 22 Jul 2020 12:05:12 -0400

> Checks on `addr_len` and `usax->sax25_ndigis` are insufficient.
> ax25_sendmsg() can go out of bounds when `usax->sax25_ndigis` equals to 7
> or 8. Fix it.
>
> It is safe to remove `usax->sax25_ndigis > AX25_MAX_DIGIS`, since
> `addr_len` is guaranteed to be less than or equal to
> `sizeof(struct full_sockaddr_ax25)`
>
> Signed-off-by: Peilin Ye <[email protected]>

Applied.

2020-07-24 23:29:46

by David Ranch

Subject: Re: [Linux-kernel-mentees] [PATCH net] AX.25: Prevent out-of-bounds read in ax25_sendmsg()

I need to ask the following question to the Linux kernel community as
the AX25 amateur radio community is already having to
work around a few broken commits that were committed 4.1.22+:

Is anyone actually _*testing*_ these proposed changes to make sure
the AX.25 and related ecosystem still work afterwards?

I've personally tried multiple times to recruit some help to get some of
these previous commits rolled back from some
recommended kernel people including even some the original authors like
Alan Cox, etc without any success. I fear that if
more commits come into the kernel without any testing, the whole AX.25
stack will become toxic and unusable.

I am not a kernel class developer but I am *personally* willing to help
out on the testing effort and even help setup regression
topologies (VMs, containers, whatever) if there is some place that they
can be ideally run in a continuous delivery.

If there is anyone also willing to help fix some of these previous
commits and get the AX.25 stack kernel back on track,
I do have a bunch of details of the commit details, details on why those
committers THOUGHT they were a good idea, etc.

--David
KI6ZHD


On 07/22/2020 06:07 PM, David Miller wrote:
> From: Peilin Ye <[email protected]>
> Date: Wed, 22 Jul 2020 12:05:12 -0400
>
>> Checks on `addr_len` and `usax->sax25_ndigis` are insufficient.
>> ax25_sendmsg() can go out of bounds when `usax->sax25_ndigis` equals to 7
>> or 8. Fix it.
>>
>> It is safe to remove `usax->sax25_ndigis > AX25_MAX_DIGIS`, since
>> `addr_len` is guaranteed to be less than or equal to
>> `sizeof(struct full_sockaddr_ax25)`
>>
>> Signed-off-by: Peilin Ye <[email protected]>
> Applied.