ppp: deflate: Fix possible crash in deflate_init

BUG: unable to handle kernel paging request at ffffffffa018f000
PGD 3270067 P4D 3270067 PUD 3271063 PMD 2307eb067 PTE 0
Oops: 0000 [#1] PREEMPT SMP
CPU: 0 PID: 4138 Comm: modprobe Not tainted 5.1.0-rc7+ #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
rel-1.9.3-0-ge2fc41e-prebuilt.qemu-project.org 04/01/2014
RIP: 0010:ppp_register_compressor+0x3e/0xd0 [ppp_generic]
Code: 98 4a 3f e2 48 8b 15 c1 67 00 00 41 8b 0c 24 48 81 fa 40 f0 19 a0
75 0e eb 35 48 8b 12 48 81 fa 40 f0 19 a0 74
RSP: 0018:ffffc90000d93c68 EFLAGS: 00010287
RAX: ffffffffa018f000 RBX: ffffffffa01a3000 RCX: 000000000000001a
RDX: ffff888230c750a0 RSI: 0000000000000000 RDI: ffffffffa019f000
RBP: ffffc90000d93c80 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffffffffa0194080
R13: ffff88822ee1a700 R14: 0000000000000000 R15: ffffc90000d93e78
FS:  00007f2339557540(0000) GS:ffff888237a00000(0000)
knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffa018f000 CR3: 000000022bde4000 CR4: 00000000000006f0
Call Trace:
 ? 0xffffffffa01a3000
 deflate_init+0x11/0x1000 [ppp_deflate]
 ? 0xffffffffa01a3000
 do_one_initcall+0x6c/0x3cc
 ? kmem_cache_alloc_trace+0x248/0x3b0
 do_init_module+0x5b/0x1f1
 load_module+0x1db1/0x2690
 ? m_show+0x1d0/0x1d0
 __do_sys_finit_module+0xc5/0xd0
 __x64_sys_finit_module+0x15/0x20
 do_syscall_64+0x6b/0x1d0
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

If ppp_deflate fails to register in deflate_init,
module initialization failed out, however
ppp_deflate_draft may has been regiestred and not
unregistered before return.
Then the seconed modprobe will trigger crash like this.
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Acked-by: Guillaume Nault <gnault@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ppp/ppp_deflate.c

@@ -610,12 +610,20 @@ static struct compressor ppp_deflate_draft = {
 
 static int __init deflate_init(void)
 {
-        int answer = ppp_register_compressor(&ppp_deflate);
-        if (answer == 0)
-                printk(KERN_INFO
-		       "PPP Deflate Compression module registered\n");
-	ppp_register_compressor(&ppp_deflate_draft);
-        return answer;
+	int rc;
+
+	rc = ppp_register_compressor(&ppp_deflate);
+	if (rc)
+		return rc;
+
+	rc = ppp_register_compressor(&ppp_deflate_draft);
+	if (rc) {
+		ppp_unregister_compressor(&ppp_deflate);
+		return rc;
+	}
+
+	pr_info("PPP Deflate Compression module registered\n");
+	return 0;
 }
 
 static void __exit deflate_cleanup(void)