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From d8482bf011cb2b173e85b65b4bf3d5061250cdb9 Mon Sep 17 00:00:00 2001
From: Donatas Abraitis <donatas@opensourcerouting.org>
Date: Mon, 23 Oct 2023 23:34:10 +0300
Subject: [PATCH] bgpd: Check mandatory attributes more carefully for UPDATE
message
If we send a crafted BGP UPDATE message without mandatory attributes, we do
not check if the length of the path attributes is zero or not. We only check
if attr->flag is at least set or not. Imagine we send only unknown transit
attribute, then attr->flag is always 0. Also, this is true only if graceful-restart
capability is received.
Reported-by: Iggy Frankovic <iggyfran@amazon.com>
Signed-off-by: Donatas Abraitis <donatas@opensourcerouting.org>
---
bgpd/bgp_attr.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)
diff --git a/bgpd/bgp_attr.c b/bgpd/bgp_attr.c
index 26fd3de..bcc4424 100644
--- a/bgpd/bgp_attr.c
+++ b/bgpd/bgp_attr.c
@@ -3400,7 +3400,8 @@ bgp_attr_unknown(struct bgp_attr_parser_args *args)
}
/* Well-known attribute check. */
-static int bgp_attr_check(struct peer *peer, struct attr *attr)
+static int bgp_attr_check(struct peer *peer, struct attr *attr,
+ bgp_size_t length)
{
uint8_t type = 0;
@@ -3409,7 +3410,8 @@ static int bgp_attr_check(struct peer *peer, struct attr *attr)
* we will pass it to be processed as a normal UPDATE without mandatory
* attributes, that could lead to harmful behavior.
*/
- if (CHECK_FLAG(peer->cap, PEER_CAP_RESTART_RCV) && !attr->flag)
+ if (CHECK_FLAG(peer->cap, PEER_CAP_RESTART_RCV) && !attr->flag &&
+ !length)
return BGP_ATTR_PARSE_WITHDRAW;
if (!CHECK_FLAG(attr->flag, ATTR_FLAG_BIT(BGP_ATTR_ORIGIN)))
@@ -3462,7 +3464,7 @@ enum bgp_attr_parse_ret bgp_attr_parse(struct peer *peer, struct attr *attr,
enum bgp_attr_parse_ret ret;
uint8_t flag = 0;
uint8_t type = 0;
- bgp_size_t length;
+ bgp_size_t length = 0;
uint8_t *startp, *endp;
uint8_t *attr_endp;
uint8_t seen[BGP_ATTR_BITMAP_SIZE];
@@ -3785,7 +3787,7 @@ enum bgp_attr_parse_ret bgp_attr_parse(struct peer *peer, struct attr *attr,
}
/* Check all mandatory well-known attributes are present */
- ret = bgp_attr_check(peer, attr);
+ ret = bgp_attr_check(peer, attr, length);
if (ret < 0)
goto done;
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