[PATCH net 04/11] batman-adv: tvlv: reject oversized TVLV packets

From: Sven Eckelmann <sven@narfation.org>

batadv_tvlv_container_ogm_append() builds a TVLV packet section from
the tvlv.container_list. The total size of this section is computed by
batadv_tvlv_container_list_size(), which sums the sizes of all registered
containers.

The return type and accumulator in batadv_tvlv_container_list_size() were
u16. If the accumulated size exceeds U16_MAX, the value wraps around,
causing the subsequent allocation in batadv_tvlv_container_ogm_append()
to be undersized. The memcpy-style copy that follows would then write
beyond the end of the allocated buffer, corrupting kernel memory.

Fix this by widening the return type of batadv_tvlv_container_list_size()
to size_t. In batadv_tvlv_container_ogm_append(), check the computed length
against U16_MAX before proceeding, and bail out as if the allocation had
failed when the limit is exceeded.

Cc: stable@kernel.org
Fixes: ef26157747d4 ("batman-adv: tvlv - basic infrastructure")
Reported-by: Yuan Tan <redacted>
Reported-by: Yifan Wu <redacted>
Reported-by: Juefei Pu <redacted>
Reported-by: Xin Liu <redacted>
Reviewed-by: Yuan Tan <redacted>
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>
---
 net/batman-adv/tvlv.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/net/batman-adv/tvlv.c b/net/batman-adv/tvlv.c
index 46ed61dbf0879..cc6ac580c6208 100644
--- a/net/batman-adv/tvlv.c
+++ b/net/batman-adv/tvlv.c

@@ -13,6 +13,7 @@
 #include <linux/gfp.h>
 #include <linux/if_ether.h>
 #include <linux/kref.h>
+#include <linux/limits.h>
 #include <linux/list.h>
 #include <linux/lockdep.h>
 #include <linux/netdevice.h>

@@ -160,10 +161,10 @@ batadv_tvlv_container_get(struct batadv_priv *bat_priv, u8 type, u8 version)
  *
  * Return: size of all currently registered tvlv containers in bytes.
  */
-static u16 batadv_tvlv_container_list_size(struct batadv_priv *bat_priv)
+static size_t batadv_tvlv_container_list_size(struct batadv_priv *bat_priv)
 {
 	struct batadv_tvlv_container *tvlv;
-	u16 tvlv_len = 0;
+	size_t tvlv_len = 0;
 
 	lockdep_assert_held(&bat_priv->tvlv.container_list_lock);
 

@@ -316,13 +317,17 @@ int batadv_tvlv_container_ogm_append(struct batadv_priv *bat_priv,
 {
 	struct batadv_tvlv_container *tvlv;
 	struct batadv_tvlv_hdr *tvlv_hdr;
-	u16 tvlv_value_len;
+	size_t tvlv_value_len;
 	void *tvlv_value;
 	int tvlv_len_ret;
 	bool ret;
 
 	spin_lock_bh(&bat_priv->tvlv.container_list_lock);
 	tvlv_value_len = batadv_tvlv_container_list_size(bat_priv);
+	if (tvlv_value_len > U16_MAX) {
+		tvlv_len_ret = -E2BIG;
+		goto end;
+	}
 
 	ret = batadv_tvlv_realloc_packet_buff(packet_buff, packet_buff_len,
 					      packet_min_len, tvlv_value_len);

-- 
2.47.3