tty: synclink_gt: Fix null-pointer-dereference in slgt_clean()

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: tty: synclink_gt: Fix null-pointer-dereference in slgt_clean() When the driver fails at alloc_hdlcdev(), and then we remove the driver module, we will get the following splat: [ 25.065966] general protection fault, probably for non-canonical address 0xdffffc0000000182: 0000 [#1] PREEMPT SMP KASAN PTI [ 25.066914] KASAN: null-ptr-deref in range [0x0000000000000c10-0x0000000000000c17] [ 25.069262] RIP: 0010:detach_hdlc_protocol+0x2a/0x3e0 [ 25.077709] Call Trace: [ 25.077924] <TASK> [ 25.078108] unregister_hdlc_device+0x16/0x30 [ 25.078481] slgt_cleanup+0x157/0x9f0 [synclink_gt] Fix this by checking whether the 'info->netdev' is a null pointer first.

References

• https://git.kernel.org/stable/c/50c341f9a2adc4c32a8ad5a39eb99d9c4a419e0d
• https://git.kernel.org/stable/c/078212ad15dbd88840c82c97f12c93d83703c8fd
• https://git.kernel.org/stable/c/ba08cbc5b53e151d0acf1930fb526fc65b7f3e65
• https://git.kernel.org/stable/c/f6e07eb7ebec53ffe81fc2489589320fbe4a6b75
• https://git.kernel.org/stable/c/d68d5e68b7f64de7170f8e04dd9b995c36b2c71c
• https://git.kernel.org/stable/c/8a95696bdc0e13f8980f05b54a3b9081963d1256
• https://git.kernel.org/stable/c/ddd67751ab86c6a65f95c35293c42f85a42ac05d
• https://git.kernel.org/stable/c/1ceb4ca9543a8a788febf6bc8dad2e605e172d5e
• https://git.kernel.org/stable/c/689ca31c542687709ba21ec2195c1fbce34fd029