linux-kernel - [PATCH 4.9 092/130] netfilter: nf_conntrack: Fix possible possible crash on module loading.

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Message-Id: <20180823074933.141143488@linuxfoundation.org>
Date:   Thu, 23 Aug 2018 09:53:28 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Sasha Levin <alexander.levin@...rosoft.com>
Subject: [PATCH 4.9 092/130] netfilter: nf_conntrack: Fix possible possible crash on module loading.

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Andrey Ryabinin <aryabinin@...tuozzo.com>

[ Upstream commit 2045cdfa1b40d66f126f3fd05604fc7c754f0022 ]

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@...tuozzo.com>
Signed-off-by: Pablo Neira Ayuso <pablo@...filter.org>
Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 net/netfilter/nf_conntrack_core.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/netfilter/nf_conntrack_core.c
+++ b/net/netfilter/nf_conntrack_core.c
@@ -1822,7 +1822,7 @@ int nf_conntrack_set_hashsize(const char
 		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);