linux-kernel - Re: [PATCH RESEND] ptp: Fixes a null pointer dereference in ptp

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Date:   Wed, 8 Nov 2023 11:26:02 +0100
From:   Przemek Kitszel <przemyslaw.kitszel@...el.com>
To:     Yuran Pereira <yuran.pereira@...mail.com>,
        <richardcochran@...il.com>, <netdev@...r.kernel.org>
CC:     <eadavis@...com>, <davem@...emloft.net>, <reibax@...il.com>,
        <linux-kernel@...r.kernel.org>,
        <linux-kernel-mentees@...ts.linuxfoundation.org>,
        <syzbot+8a78ecea7ac1a2ea26e5@...kaller.appspotmail.com>
Subject: Re: [PATCH RESEND] ptp: Fixes a null pointer dereference in ptp_ioctl

On 11/8/23 11:15, Przemek Kitszel wrote:
> On 11/7/23 21:48, Yuran Pereira wrote:
>> Syzkaller found a null pointer dereference in ptp_ioctl

Ugh, I just noticed that this is a fixed version of previous attempt,
for those please always bump version and include changelog, please
also comply with:
https://www.kernel.org/doc/html/next/process/maintainer-netdev.html

if only to don't fool random reviewers
(I somewhat assumed that you have just rebased some old patch,
PATCH RESEND was misleading here)

>> originating from the lack of a null check for tsevq.
>>
>> ```
>> general protection fault, probably for non-canonical
>>     address 0xdffffc000000020b: 0000 [#1] PREEMPT SMP KASAN
>> KASAN: probably user-memory-access in range
>>     [0x0000000000001058-0x000000000000105f]
>> CPU: 0 PID: 5053 Comm: syz-executor353 Not tainted
>>     6.6.0-syzkaller-10396-g4652b8e4f3ff #0
>> Hardware name: Google Google Compute Engine/Google Compute Engine,
>>     BIOS Google 10/09/2023
>> RIP: 0010:ptp_ioctl+0xcb7/0x1d10 drivers/ptp/ptp_chardev.c:476
>> ...
>> Call Trace:
>>   <TASK>
>>   posix_clock_ioctl+0xf8/0x160 kernel/time/posix-clock.c:86
>>   vfs_ioctl fs/ioctl.c:51 [inline]
>>   __do_sys_ioctl fs/ioctl.c:871 [inline]
>>   __se_sys_ioctl fs/ioctl.c:857 [inline]
>>   __x64_sys_ioctl+0x18f/0x210 fs/ioctl.c:857
>>   do_syscall_x64 arch/x86/entry/common.c:51 [inline]
>>   do_syscall_64+0x3f/0x110 arch/x86/entry/common.c:82
>>   entry_SYSCALL_64_after_hwframe+0x63/0x6b
>> ```
>>
>> This patch fixes the issue by adding a check for tsevq and
>> ensuring ptp_ioctl returns with an error if tsevq is null.
>>
>> Reported-by: syzbot+8a78ecea7ac1a2ea26e5@...kaller.appspotmail.com
>> Closes: https://syzkaller.appspot.com/bug?extid=8a78ecea7ac1a2ea26e5
>> Fixes: c5a445b1e934 ("ptp: support event queue reader channel masks")
>> Signed-off-by: Yuran Pereira <yuran.pereira@...mail.com>
>> ---
>>   drivers/ptp/ptp_chardev.c | 2 ++
>>   1 file changed, 2 insertions(+)
>>
>> diff --git a/drivers/ptp/ptp_chardev.c b/drivers/ptp/ptp_chardev.c
>> index 282cd7d24077..5b36c34629a0 100644
>> --- a/drivers/ptp/ptp_chardev.c
>> +++ b/drivers/ptp/ptp_chardev.c
>> @@ -173,6 +173,8 @@ long ptp_ioctl(struct posix_clock_context 
>> *pccontext, unsigned int cmd,
>>       int enable, err = 0;
>>       tsevq = pccontext->private_clkdata;
>> +    if (!tsevq)
>> +        return -EINVAL;
>>       switch (cmd) {
> 
> Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@...el.com>
> 

Still applies, code is fine, thanks!