From dabda47cb8c4f0fe53afa6899e6dfe4f2046ed4d Mon Sep 17 00:00:00 2001
From: Andrey Ryabinin <aryabinin@virtuozzo.com>
Date: Fri, 6 Jul 2018 16:38:53 +0300
Subject: [PATCH] netfilter: nf_conntrack: Fix possible possible crash on
 module loading.
Git-commit: 2045cdfa1b40d66f126f3fd05604fc7c754f0022
Patch-mainline: v4.18-rc6
References: git-fixes

Loading the nf_conntrack module with doubled hashsize parameter, i.e.
	  modprobe nf_conntrack hashsize=12345 hashsize=12345
causes NULL-ptr deref.

If 'hashsize' specified twice, the nf_conntrack_set_hashsize() function
will be called also twice.
The first nf_conntrack_set_hashsize() call will set the
'nf_conntrack_htable_size' variable:

	nf_conntrack_set_hashsize()
		...
		/* On boot, we can set this without any fancy locking. */
		if (!nf_conntrack_htable_size)
			return param_set_uint(val, kp);

But on the second invocation, the nf_conntrack_htable_size is already set,
so the nf_conntrack_set_hashsize() will take a different path and call
the nf_conntrack_hash_resize() function. Which will crash on the attempt
to dereference 'nf_conntrack_hash' pointer:

	BUG: unable to handle kernel NULL pointer dereference at 0000000000000000
	RIP: 0010:nf_conntrack_hash_resize+0x255/0x490 [nf_conntrack]
	Call Trace:
	 nf_conntrack_set_hashsize+0xcd/0x100 [nf_conntrack]
	 parse_args+0x1f9/0x5a0
	 load_module+0x1281/0x1a50
	 __se_sys_finit_module+0xbe/0xf0
	 do_syscall_64+0x7c/0x390
	 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Fix this, by checking !nf_conntrack_hash instead of
!nf_conntrack_htable_size. nf_conntrack_hash will be initialized only
after the module loaded, so the second invocation of the
nf_conntrack_set_hashsize() won't crash, it will just reinitialize
nf_conntrack_htable_size again.

Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Denis Kirjanov <denis.kirjanov@suse.com>
---
 net/netfilter/nf_conntrack_core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c
index 02b0aa280238..12de7617cab6 100644
--- a/net/netfilter/nf_conntrack_core.c
+++ b/net/netfilter/nf_conntrack_core.c
@@ -1846,7 +1846,7 @@ int nf_conntrack_set_hashsize(const char *val, struct kernel_param *kp)
 		return -EOPNOTSUPP;
 
 	/* On boot, we can set this without any fancy locking. */
-	if (!nf_conntrack_htable_size)
+	if (!nf_conntrack_hash)
 		return param_set_uint(val, kp);
 
 	rc = kstrtouint(val, 0, &hashsize);
-- 
2.16.4