CVE-2022-49916: rose: Fix NULL pointer dereference in rose_send_frame()

In the Linux kernel, the following vulnerability has been resolved:

rose: Fix NULL pointer dereference in rosesendframe()

The syzkaller reported an issue:

KASAN: null-ptr-deref in range [0x0000000000000380-0x0000000000000387] CPU: 0 PID: 4069 Comm: kworker/0:15 Not tainted 6.0.0-syzkaller-02734-g0326074ff465 #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/22/2022 Workqueue: rcugp srcuinvokecallbacks RIP: 0010:rosesendframe+0x1dd/0x2f0 net/rose/roselink.c:101 Call Trace: <IRQ> rosetransmitclearrequest+0x1d5/0x290 net/rose/roselink.c:255 roserxcallrequest+0x4c0/0x1bc0 net/rose/afrose.c:1009 roseloopbacktimer+0x19e/0x590 net/rose/roseloopback.c:111 calltimerfn+0x1a0/0x6b0 kernel/time/timer.c:1474 expiretimers kernel/time/timer.c:1519 [inline] runtimers.part.0+0x674/0xa80 kernel/time/timer.c:1790 runtimers kernel/time/timer.c:1768 [inline] runtimersoftirq+0xb3/0x1d0 kernel/time/timer.c:1803 dosoftirq+0x1d0/0x9c8 kernel/softirq.c:571 [...] </IRQ>

It triggers NULL pointer dereference when 'neigh->dev->devaddr' is called in the rosesendframe(). It's the first occurrence of the neigh is in roseloopbacktimer() as roseloopbackneigh', and the 'dev' in 'roseloopbackneigh' is initialized sa nullptr.

It had been fixed by commit 3b3fd068c56e3fbea30090859216a368398e39bf ("rose: Fix Null pointer dereference in rosesendframe()") ever. But it's introduced by commit 3c53cd65dece47dd1f9d3a809f32e59d1d87b2b8 ("rose: check NULL roseloopbackneigh->loopback") again.

We fix it by add NULL check in rosetransmitclearrequest(). When the 'dev' in 'neigh' is NULL, we don't reply the request and just clear it.

syzkaller don't provide repro, and I provide a syz repro like: r0 = syzinitnetsocket$btsco(0x1f, 0x5, 0x2) ioctl$sockinetSIOCSIFFLAGS(r0, 0x8914, &(0x7f0000000180)={'rose0\x00', 0x201}) r1 = syzinitnetsocket$rose(0xb, 0x5, 0x0) bind$rose(r1, &(0x7f00000000c0)=@full={0xb, @dev, @null, 0x0, [@null, @null, @netrom, @netrom, @default, @null]}, 0x40) connect$rose(r1, &(0x7f0000000240)=@short={0xb, @dev={0xbb, 0xbb, 0xbb, 0x1, 0x0}, @remote={0xcc, 0xcc, 0xcc, 0xcc, 0xcc, 0xcc, 0x1}, 0x1, @netrom={0xbb, 0xbb, 0xbb, 0xbb, 0xbb, 0x0, 0x0}}, 0x1c)