* Re: [PATCH] net: 6pack: fix slab-out-of-bounds in decode_data
2021-08-13 14:58 ` Dan Carpenter
@ 2021-08-13 15:09 ` Pavel Skripkin
2021-08-13 15:14 ` [PATCH v2] " Pavel Skripkin
2021-08-14 0:23 ` [PATCH] " Kevin Dawson
2 siblings, 0 replies; 10+ messages in thread
From: Pavel Skripkin @ 2021-08-13 15:09 UTC (permalink / raw)
To: Dan Carpenter
Cc: ajk, davem, kuba, linux-hams, netdev, linux-kernel,
syzbot+fc8cd9a673d4577fb2e4
On 8/13/21 5:58 PM, Dan Carpenter wrote:
> On Fri, Aug 13, 2021 at 02:28:55PM +0300, Pavel Skripkin wrote:
>> Syzbot reported slab-out-of bounds write in decode_data().
>> The problem was in missing validation checks.
>>
>> Syzbot's reproducer generated malicious input, which caused
>> decode_data() to be called a lot in sixpack_decode(). Since
>> rx_count_cooked is only 400 bytes and noone reported before,
>> that 400 bytes is not enough, let's just check if input is malicious
>> and complain about buffer overrun.
>>
>> Fail log:
>> ==================================================================
>> BUG: KASAN: slab-out-of-bounds in drivers/net/hamradio/6pack.c:843
>> Write of size 1 at addr ffff888087c5544e by task kworker/u4:0/7
>>
>> CPU: 0 PID: 7 Comm: kworker/u4:0 Not tainted 5.6.0-rc3-syzkaller #0
>> ...
>> Workqueue: events_unbound flush_to_ldisc
>> Call Trace:
>> __dump_stack lib/dump_stack.c:77 [inline]
>> dump_stack+0x197/0x210 lib/dump_stack.c:118
>> print_address_description.constprop.0.cold+0xd4/0x30b mm/kasan/report.c:374
>> __kasan_report.cold+0x1b/0x32 mm/kasan/report.c:506
>> kasan_report+0x12/0x20 mm/kasan/common.c:641
>> __asan_report_store1_noabort+0x17/0x20 mm/kasan/generic_report.c:137
>> decode_data.part.0+0x23b/0x270 drivers/net/hamradio/6pack.c:843
>> decode_data drivers/net/hamradio/6pack.c:965 [inline]
>> sixpack_decode drivers/net/hamradio/6pack.c:968 [inline]
>>
>> Reported-and-tested-by: syzbot+fc8cd9a673d4577fb2e4@syzkaller.appspotmail.com
>> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
>> Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
>> ---
>> drivers/net/hamradio/6pack.c | 6 ++++++
>> 1 file changed, 6 insertions(+)
>>
>> diff --git a/drivers/net/hamradio/6pack.c b/drivers/net/hamradio/6pack.c
>> index fcf3af76b6d7..f4ffc2a80ab7 100644
>> --- a/drivers/net/hamradio/6pack.c
>> +++ b/drivers/net/hamradio/6pack.c
>> @@ -827,6 +827,12 @@ static void decode_data(struct sixpack *sp, unsigned char inbyte)
>> return;
>> }
>>
>> + if (sp->rx_count_cooked + 3 >= sizeof(sp->cooked_buf)) {
>
> It should be + 2 instead of + 3.
>
> We write three bytes. idx, idx + 1, idx + 2. Otherwise, good fix!
>
Indeed. Will fix in v2, thank you for pointing it out!
With regards,
Pavel Skripkin
^ permalink raw reply [flat|nested] 10+ messages in thread* [PATCH v2] net: 6pack: fix slab-out-of-bounds in decode_data
2021-08-13 14:58 ` Dan Carpenter
2021-08-13 15:09 ` Pavel Skripkin
@ 2021-08-13 15:14 ` Pavel Skripkin
2021-08-13 21:09 ` Dan Carpenter
2021-08-16 10:10 ` patchwork-bot+netdevbpf
2021-08-14 0:23 ` [PATCH] " Kevin Dawson
2 siblings, 2 replies; 10+ messages in thread
From: Pavel Skripkin @ 2021-08-13 15:14 UTC (permalink / raw)
To: ajk, davem, kuba
Cc: linux-hams, netdev, linux-kernel, dan.carpenter, Pavel Skripkin,
syzbot+fc8cd9a673d4577fb2e4
Syzbot reported slab-out-of bounds write in decode_data().
The problem was in missing validation checks.
Syzbot's reproducer generated malicious input, which caused
decode_data() to be called a lot in sixpack_decode(). Since
rx_count_cooked is only 400 bytes and noone reported before,
that 400 bytes is not enough, let's just check if input is malicious
and complain about buffer overrun.
Fail log:
==================================================================
BUG: KASAN: slab-out-of-bounds in drivers/net/hamradio/6pack.c:843
Write of size 1 at addr ffff888087c5544e by task kworker/u4:0/7
CPU: 0 PID: 7 Comm: kworker/u4:0 Not tainted 5.6.0-rc3-syzkaller #0
...
Workqueue: events_unbound flush_to_ldisc
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x197/0x210 lib/dump_stack.c:118
print_address_description.constprop.0.cold+0xd4/0x30b mm/kasan/report.c:374
__kasan_report.cold+0x1b/0x32 mm/kasan/report.c:506
kasan_report+0x12/0x20 mm/kasan/common.c:641
__asan_report_store1_noabort+0x17/0x20 mm/kasan/generic_report.c:137
decode_data.part.0+0x23b/0x270 drivers/net/hamradio/6pack.c:843
decode_data drivers/net/hamradio/6pack.c:965 [inline]
sixpack_decode drivers/net/hamradio/6pack.c:968 [inline]
Reported-and-tested-by: syzbot+fc8cd9a673d4577fb2e4@syzkaller.appspotmail.com
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
---
Changes in v2:
+ 3 -> +2 (Reported by Dan Carpenter)
---
drivers/net/hamradio/6pack.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/drivers/net/hamradio/6pack.c b/drivers/net/hamradio/6pack.c
index fcf3af76b6d7..8fe8887d506a 100644
--- a/drivers/net/hamradio/6pack.c
+++ b/drivers/net/hamradio/6pack.c
@@ -827,6 +827,12 @@ static void decode_data(struct sixpack *sp, unsigned char inbyte)
return;
}
+ if (sp->rx_count_cooked + 2 >= sizeof(sp->cooked_buf)) {
+ pr_err("6pack: cooked buffer overrun, data loss\n");
+ sp->rx_count = 0;
+ return;
+ }
+
buf = sp->raw_buf;
sp->cooked_buf[sp->rx_count_cooked++] =
buf[0] | ((buf[1] << 2) & 0xc0);
--
2.32.0
^ permalink raw reply related [flat|nested] 10+ messages in thread* Re: [PATCH v2] net: 6pack: fix slab-out-of-bounds in decode_data
2021-08-13 15:14 ` [PATCH v2] " Pavel Skripkin
@ 2021-08-13 21:09 ` Dan Carpenter
2021-08-13 21:32 ` Pavel Skripkin
2021-08-16 10:10 ` patchwork-bot+netdevbpf
1 sibling, 1 reply; 10+ messages in thread
From: Dan Carpenter @ 2021-08-13 21:09 UTC (permalink / raw)
To: Pavel Skripkin
Cc: ajk, davem, kuba, linux-hams, netdev, linux-kernel,
syzbot+fc8cd9a673d4577fb2e4
Great!
Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
regards,
dan carpenter
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH v2] net: 6pack: fix slab-out-of-bounds in decode_data
2021-08-13 21:09 ` Dan Carpenter
@ 2021-08-13 21:32 ` Pavel Skripkin
0 siblings, 0 replies; 10+ messages in thread
From: Pavel Skripkin @ 2021-08-13 21:32 UTC (permalink / raw)
To: Dan Carpenter
Cc: ajk, davem, kuba, linux-hams, netdev, linux-kernel,
syzbot+fc8cd9a673d4577fb2e4
On 8/14/21 12:09 AM, Dan Carpenter wrote:
> Great!
>
> Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
>
Thank you, Dan!
With regards,
Pavel Skripkin
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH v2] net: 6pack: fix slab-out-of-bounds in decode_data
2021-08-13 15:14 ` [PATCH v2] " Pavel Skripkin
2021-08-13 21:09 ` Dan Carpenter
@ 2021-08-16 10:10 ` patchwork-bot+netdevbpf
1 sibling, 0 replies; 10+ messages in thread
From: patchwork-bot+netdevbpf @ 2021-08-16 10:10 UTC (permalink / raw)
To: Pavel Skripkin
Cc: ajk, davem, kuba, linux-hams, netdev, linux-kernel,
dan.carpenter, syzbot+fc8cd9a673d4577fb2e4
Hello:
This patch was applied to netdev/net.git (refs/heads/master):
On Fri, 13 Aug 2021 18:14:33 +0300 you wrote:
> Syzbot reported slab-out-of bounds write in decode_data().
> The problem was in missing validation checks.
>
> Syzbot's reproducer generated malicious input, which caused
> decode_data() to be called a lot in sixpack_decode(). Since
> rx_count_cooked is only 400 bytes and noone reported before,
> that 400 bytes is not enough, let's just check if input is malicious
> and complain about buffer overrun.
>
> [...]
Here is the summary with links:
- [v2] net: 6pack: fix slab-out-of-bounds in decode_data
https://git.kernel.org/netdev/net/c/19d1532a1876
You are awesome, thank you!
--
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH] net: 6pack: fix slab-out-of-bounds in decode_data
2021-08-13 14:58 ` Dan Carpenter
2021-08-13 15:09 ` Pavel Skripkin
2021-08-13 15:14 ` [PATCH v2] " Pavel Skripkin
@ 2021-08-14 0:23 ` Kevin Dawson
2021-08-14 14:17 ` Pavel Skripkin
2 siblings, 1 reply; 10+ messages in thread
From: Kevin Dawson @ 2021-08-14 0:23 UTC (permalink / raw)
To: Dan Carpenter
Cc: Pavel Skripkin, ajk, davem, kuba, linux-hams, netdev,
linux-kernel, syzbot+fc8cd9a673d4577fb2e4
On Fri, Aug 13, 2021 at 05:58:34PM +0300, Dan Carpenter wrote:
> On Fri, Aug 13, 2021 at 02:28:55PM +0300, Pavel Skripkin wrote:
> > Syzbot reported slab-out-of bounds write in decode_data().
> > The problem was in missing validation checks.
> >
> > Syzbot's reproducer generated malicious input, which caused
> > decode_data() to be called a lot in sixpack_decode(). Since
> > rx_count_cooked is only 400 bytes and noone reported before,
> > that 400 bytes is not enough, let's just check if input is malicious
> > and complain about buffer overrun.
> >
> > ...
> >
> > diff --git a/drivers/net/hamradio/6pack.c b/drivers/net/hamradio/6pack.c
> > index fcf3af76b6d7..f4ffc2a80ab7 100644
> > --- a/drivers/net/hamradio/6pack.c
> > +++ b/drivers/net/hamradio/6pack.c
> > @@ -827,6 +827,12 @@ static void decode_data(struct sixpack *sp, unsigned char inbyte)
> > return;
> > }
> >
> > + if (sp->rx_count_cooked + 3 >= sizeof(sp->cooked_buf)) {
>
> It should be + 2 instead of + 3.
>
> We write three bytes. idx, idx + 1, idx + 2. Otherwise, good fix!
I would suggest that the statement be:
if (sp->rx_count_cooked + 3 > sizeof(sp->cooked_buf)) {
or even, because it's a buffer overrun test:
if (sp->rx_count_cooked > sizeof(sp->cooked_buf) - 3) {
This is because if there are three bytes being written, that is the number that should be obvious in the test.
I haven't looked at the surrounding code and there may be some other consideration why the "+ 2 >=" rather than "+ 3 >" (and from the description of "idx, idx + 1, idx + 2", I suspect it's visual consistency), so if that is important, feel free to adjust as required.
Thanks,
Kevin
^ permalink raw reply [flat|nested] 10+ messages in thread* Re: [PATCH] net: 6pack: fix slab-out-of-bounds in decode_data
2021-08-14 0:23 ` [PATCH] " Kevin Dawson
@ 2021-08-14 14:17 ` Pavel Skripkin
2021-08-16 7:13 ` Dan Carpenter
0 siblings, 1 reply; 10+ messages in thread
From: Pavel Skripkin @ 2021-08-14 14:17 UTC (permalink / raw)
To: Kevin Dawson, Dan Carpenter
Cc: ajk, davem, kuba, linux-hams, netdev, linux-kernel,
syzbot+fc8cd9a673d4577fb2e4
On 8/14/21 3:23 AM, Kevin Dawson wrote:
> On Fri, Aug 13, 2021 at 05:58:34PM +0300, Dan Carpenter wrote:
>> On Fri, Aug 13, 2021 at 02:28:55PM +0300, Pavel Skripkin wrote:
>> > Syzbot reported slab-out-of bounds write in decode_data().
>> > The problem was in missing validation checks.
>> >
>> > Syzbot's reproducer generated malicious input, which caused
>> > decode_data() to be called a lot in sixpack_decode(). Since
>> > rx_count_cooked is only 400 bytes and noone reported before,
>> > that 400 bytes is not enough, let's just check if input is malicious
>> > and complain about buffer overrun.
>> >
>> > ...
>> >
>> > diff --git a/drivers/net/hamradio/6pack.c b/drivers/net/hamradio/6pack.c
>> > index fcf3af76b6d7..f4ffc2a80ab7 100644
>> > --- a/drivers/net/hamradio/6pack.c
>> > +++ b/drivers/net/hamradio/6pack.c
>> > @@ -827,6 +827,12 @@ static void decode_data(struct sixpack *sp, unsigned char inbyte)
>> > return;
>> > }
>> >
>> > + if (sp->rx_count_cooked + 3 >= sizeof(sp->cooked_buf)) {
>>
>> It should be + 2 instead of + 3.
>>
>> We write three bytes. idx, idx + 1, idx + 2. Otherwise, good fix!
>
> I would suggest that the statement be:
>
> if (sp->rx_count_cooked + 3 > sizeof(sp->cooked_buf)) {
>
> or even, because it's a buffer overrun test:
>
> if (sp->rx_count_cooked > sizeof(sp->cooked_buf) - 3) {
>
Hmm, I think, it will be more straightforward for someone not aware
about driver details.
@Dan, can I add your Reviewed-by tag to v3 and what do you think about
Kevin's suggestion?
> This is because if there are three bytes being written, that is the number that should be obvious in the test.
>
> I haven't looked at the surrounding code and there may be some other consideration why the "+ 2 >=" rather than "+ 3 >" (and from the description of "idx, idx + 1, idx + 2", I suspect it's visual consistency), so if that is important, feel free to adjust as required.
>
With regards,
Pavel Skripkin
^ permalink raw reply [flat|nested] 10+ messages in thread* Re: [PATCH] net: 6pack: fix slab-out-of-bounds in decode_data
2021-08-14 14:17 ` Pavel Skripkin
@ 2021-08-16 7:13 ` Dan Carpenter
0 siblings, 0 replies; 10+ messages in thread
From: Dan Carpenter @ 2021-08-16 7:13 UTC (permalink / raw)
To: Pavel Skripkin
Cc: Kevin Dawson, ajk, davem, kuba, linux-hams, netdev, linux-kernel,
syzbot+fc8cd9a673d4577fb2e4
On Sat, Aug 14, 2021 at 05:17:44PM +0300, Pavel Skripkin wrote:
> On 8/14/21 3:23 AM, Kevin Dawson wrote:
> > On Fri, Aug 13, 2021 at 05:58:34PM +0300, Dan Carpenter wrote:
> > > On Fri, Aug 13, 2021 at 02:28:55PM +0300, Pavel Skripkin wrote:
> > > > Syzbot reported slab-out-of bounds write in decode_data().
> > > > The problem was in missing validation checks.
> > > > > Syzbot's reproducer generated malicious input, which caused
> > > > decode_data() to be called a lot in sixpack_decode(). Since
> > > > rx_count_cooked is only 400 bytes and noone reported before,
> > > > that 400 bytes is not enough, let's just check if input is malicious
> > > > and complain about buffer overrun.
> > > > > ...
> > > > > diff --git a/drivers/net/hamradio/6pack.c
> > > b/drivers/net/hamradio/6pack.c
> > > > index fcf3af76b6d7..f4ffc2a80ab7 100644
> > > > --- a/drivers/net/hamradio/6pack.c
> > > > +++ b/drivers/net/hamradio/6pack.c
> > > > @@ -827,6 +827,12 @@ static void decode_data(struct sixpack *sp, unsigned char inbyte)
> > > > return;
> > > > }
> > > > > + if (sp->rx_count_cooked + 3 >= sizeof(sp->cooked_buf)) {
> > >
> > > It should be + 2 instead of + 3.
> > >
> > > We write three bytes. idx, idx + 1, idx + 2. Otherwise, good fix!
> >
> > I would suggest that the statement be:
> >
> > if (sp->rx_count_cooked + 3 > sizeof(sp->cooked_buf)) {
> >
> > or even, because it's a buffer overrun test:
> >
> > if (sp->rx_count_cooked > sizeof(sp->cooked_buf) - 3) {
> >
>
> Hmm, I think, it will be more straightforward for someone not aware about
> driver details.
>
> @Dan, can I add your Reviewed-by tag to v3 and what do you think about
> Kevin's suggestion?
>
I don't care. Sure. I'm also fine with leaving it as is. I've been
using "idx + 2 >= sizeof()" enough recently that it has become an idiom
for me. But that's probably a bias on my part.
I guess "idx + 3 > sizeof()" is probably the most readable. Moving
the + 3 to the other side would prevent integer overflows but we're not
concerned about that here and no need to over engineer things if it
hurts readability.
regards,
dan carpenter
^ permalink raw reply [flat|nested] 10+ messages in thread