Syzkaller found a null pointer dereference in ptp_ioctl
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.

Dashboard link: https://syzkaller.appspot.com/bug?extid=8a78ecea7ac1a2ea26e5
Reported-by: syzbot+8a78ecea7ac1a2ea26e5@syzkaller.appspotmail.com
Fixes: c5a445b1e934 ("ptp: support event queue reader channel masks")

Signed-off-by: Yuran Pereira <yuran.pereira@hotmail.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) {
 
-- 
2.25.1

On Mon,  6 Nov 2023 06:18:29 +0530 Yuran Pereira wrote:
> This patch fixes the issue by adding a check for tsevq and
> ensuring ptp_ioctl returns with an error if tsevq is null.
> 
> Dashboard link: https://syzkaller.appspot.com/bug?extid=8a78ecea7ac1a2ea26e5

Just Link:

> Reported-by: syzbot+8a78ecea7ac1a2ea26e5@syzkaller.appspotmail.com
> Fixes: c5a445b1e934 ("ptp: support event queue reader channel masks")
> 

No empty lines between tags.

> Signed-off-by: Yuran Pereira <yuran.pereira@hotmail.com>

When you repost please make sure you CC everyone get_maintainer 
(run on  the patch file, not the paths) points out.
And CC Edward Adam Davis <eadavis@qq.com> since his fixing similar
issues.
-- 
pw-bot: cr

Hey Jakub,
On Tue, Nov 07, 2023 at 10:00:34AM -0800, Jakub Kicinski wrote:
> 
> Just Link:
> 
> > Reported-by: syzbot+8a78ecea7ac1a2ea26e5@syzkaller.appspotmail.com
> > Fixes: c5a445b1e934 ("ptp: support event queue reader channel masks")
> > 
> 
> No empty lines between tags.
> 
Rookie mistake from me. I will pay better attention next time.

> 
> When you repost please make sure you CC everyone get_maintainer 
> (run on  the patch file, not the paths) points out.
Interesting, I always run get_maintainer on the modified file
will do it on the patch file too from now on.

> And CC Edward Adam Davis <eadavis@qq.com> since his fixing similar
> issues.
Alright, I'll do that.

Thank you for the feedback.

Yuran