[PATCH 4.17 225/324] netfilter: nf_conntrack: Fix possible possible crash on module loading.

From: Greg Kroah-Hartman
Date: Thu Aug 23 2018 - 05:01:40 EST

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


From: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>

[ 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:

/* 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]

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@xxxxxxxxxxxxx>
Signed-off-by: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
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
@@ -1972,7 +1972,7 @@ int nf_conntrack_set_hashsize(const char

/* 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);