[PATCH 5.15 053/136] netfilter: ebtables: reject blobs that dont provide all entry points

Greg Kroah-Hartman
2022-08-29T11:09:25Z

From: Florian Westphal <fw@strlen.de>

[ Upstream commit 7997eff82828304b780dc0a39707e1946d6f1ebf ]

Harshit Mogalapalli says:
In ebt_do_table() function dereferencing 'private->hook_entry[hook]'
can lead to NULL pointer dereference. [..] Kernel panic:

general protection fault, probably for non-canonical address 0xdffffc0000000005: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000028-0x000000000000002f]
[..]
RIP: 0010:ebt_do_table+0x1dc/0x1ce0
Code: 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 5c 16 00 00 48 b8 00 00 00 00 00 fc ff df 49 8b 6c df 08 48 8d 7d 2c 48 89 fa 48 c1 ea 03 <0f> b6 14 02 48 89 f8 83 e0 07 83 c0 03 38 d0 7c 08 84 d2 0f 85 88
[..]
Call Trace:
nf_hook_slow+0xb1/0x170
__br_forward+0x289/0x730
maybe_deliver+0x24b/0x380
br_flood+0xc6/0x390
br_dev_xmit+0xa2e/0x12c0

For some reason ebtables rejects blobs that provide entry points that are
not supported by the table, but what it should instead reject is the
opposite: blobs that DO NOT provide an entry point supported by the table.

t->valid_hooks is the bitmask of hooks (input, forward ...) that will see
packets. Providing an entry point that is not support is harmless
(never called/used), but the inverse isn't: it results in a crash
because the ebtables traverser doesn't expect a NULL blob for a location
its receiving packets for.

Instead of fixing all the individual checks, do what iptables is doing and
reject all blobs that differ from the expected hooks.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reported-by: Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>
Reported-by: syzkaller <syzkaller@googlegroups.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
include/linux/netfilter_bridge/ebtables.h | 4 ----
net/bridge/netfilter/ebtable_broute.c | 8 --------
net/bridge/netfilter/ebtable_filter.c | 8 --------
net/bridge/netfilter/ebtable_nat.c | 8 --------
net/bridge/netfilter/ebtables.c | 8 +-------
5 files changed, 1 insertion(+), 35 deletions(-)

diff --git a/include/linux/netfilter_bridge/ebtables.h b/include/linux/netfilter_bridge/ebtables.h
index 10a01978bc0d3..bde9db771ae41 100644
--- a/include/linux/netfilter_bridge/ebtables.h
+++ b/include/linux/netfilter_bridge/ebtables.h
@@ -94,10 +94,6 @@ struct ebt_table {
struct ebt_replace_kernel *table;
unsigned int valid_hooks;
rwlock_t lock;
- /* e.g. could be the table explicitly only allows certain
- * matches, targets, ... 0 == let it in */
- int (*check)(const struct ebt_table_info *info,
- unsigned int valid_hooks);
/* the data used by the kernel */
struct ebt_table_info *private;
struct nf_hook_ops *ops;
diff --git a/net/bridge/netfilter/ebtable_broute.c b/net/bridge/netfilter/ebtable_broute.c
index a7af4eaff17d3..3d4ea774d7e8f 100644
--- a/net/bridge/netfilter/ebtable_broute.c
+++ b/net/bridge/netfilter/ebtable_broute.c
@@ -36,18 +36,10 @@ static struct ebt_replace_kernel initial_table = {
.entries = (char *)&initial_chain,
};

-static int check(const struct ebt_table_info *info, unsigned int valid_hooks)
-{
- if (valid_hooks & ~(1 << NF_BR_BROUTING))
- return -EINVAL;
- return 0;
-}
-
static const struct ebt_table broute_table = {
.name = "broute",
.table = &initial_table,
.valid_hooks = 1 << NF_BR_BROUTING,
- .check = check,
.me = THIS_MODULE,
};

diff --git a/net/bridge/netfilter/ebtable_filter.c b/net/bridge/netfilter/ebtable_filter.c
index c0b121df4a9af..257d63b5dec16 100644
--- a/net/bridge/netfilter/ebtable_filter.c
+++ b/net/bridge/netfilter/ebtable_filter.c
@@ -43,18 +43,10 @@ static struct ebt_replace_kernel initial_table = {
.entries = (char *)initial_chains,
};

-static int check(const struct ebt_table_info *info, unsigned int valid_hooks)
-{
- if (valid_hooks & ~FILTER_VALID_HOOKS)
- return -EINVAL;
- return 0;
-}
-
static const struct ebt_table frame_filter = {
.name = "filter",
.table = &initial_table,
.valid_hooks = FILTER_VALID_HOOKS,
- .check = check,
.me = THIS_MODULE,
};

diff --git a/net/bridge/netfilter/ebtable_nat.c b/net/bridge/netfilter/ebtable_nat.c
index 4078151c224fb..39179c2cf87d2 100644
--- a/net/bridge/netfilter/ebtable_nat.c
+++ b/net/bridge/netfilter/ebtable_nat.c
@@ -43,18 +43,10 @@ static struct ebt_replace_kernel initial_table = {
.entries = (char *)initial_chains,
};

-static int check(const struct ebt_table_info *info, unsigned int valid_hooks)
-{
- if (valid_hooks & ~NAT_VALID_HOOKS)
- return -EINVAL;
- return 0;
-}
-
static const struct ebt_table frame_nat = {
.name = "nat",
.table = &initial_table,
.valid_hooks = NAT_VALID_HOOKS,
- .check = check,
.me = THIS_MODULE,
};

diff --git a/net/bridge/netfilter/ebtables.c b/net/bridge/netfilter/ebtables.c
index ba045f35114dd..8905fe2fe023d 100644
--- a/net/bridge/netfilter/ebtables.c
+++ b/net/bridge/netfilter/ebtables.c
@@ -1040,8 +1040,7 @@ static int do_replace_finish(struct net *net, struct ebt_replace *repl,
goto free_iterate;
}

- /* the table doesn't like it */
- if (t->check && (ret = t->check(newinfo, repl->valid_hooks)))
+ if (repl->valid_hooks != t->valid_hooks)
goto free_unlock;

if (repl->num_counters && repl->num_counters != t->private->nentries) {
@@ -1231,11 +1230,6 @@ int ebt_register_table(struct net *net, const struct ebt_table *input_table,
if (ret != 0)
goto free_chainstack;

- if (table->check && table->check(newinfo, table->valid_hooks)) {
- ret = -EINVAL;
- goto free_chainstack;
- }
-
table->private = newinfo;
rwlock_init(&table->lock);
mutex_lock(&ebt_mutex);
--
2.35.1