Patch "rtnetlink: fix error logic of IFLA_BRIDGE_FLAGS writing back" has been added to the 5.15-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    rtnetlink: fix error logic of IFLA_BRIDGE_FLAGS writing back

to the 5.15-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     rtnetlink-fix-error-logic-of-ifla_bridge_flags-writi.patch
and it can be found in the queue-5.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit ac5cea766854656b623a23a5d1370b9ea54d0fce
Author: Lin Ma <linma@xxxxxxxxxx>
Date:   Tue Feb 27 20:11:28 2024 +0800

    rtnetlink: fix error logic of IFLA_BRIDGE_FLAGS writing back
    
    [ Upstream commit 743ad091fb46e622f1b690385bb15e3cd3daf874 ]
    
    In the commit d73ef2d69c0d ("rtnetlink: let rtnl_bridge_setlink checks
    IFLA_BRIDGE_MODE length"), an adjustment was made to the old loop logic
    in the function `rtnl_bridge_setlink` to enable the loop to also check
    the length of the IFLA_BRIDGE_MODE attribute. However, this adjustment
    removed the `break` statement and led to an error logic of the flags
    writing back at the end of this function.
    
    if (have_flags)
        memcpy(nla_data(attr), &flags, sizeof(flags));
        // attr should point to IFLA_BRIDGE_FLAGS NLA !!!
    
    Before the mentioned commit, the `attr` is granted to be IFLA_BRIDGE_FLAGS.
    However, this is not necessarily true fow now as the updated loop will let
    the attr point to the last NLA, even an invalid NLA which could cause
    overflow writes.
    
    This patch introduces a new variable `br_flag` to save the NLA pointer
    that points to IFLA_BRIDGE_FLAGS and uses it to resolve the mentioned
    error logic.
    
    Fixes: d73ef2d69c0d ("rtnetlink: let rtnl_bridge_setlink checks IFLA_BRIDGE_MODE length")
    Signed-off-by: Lin Ma <linma@xxxxxxxxxx>
    Acked-by: Nikolay Aleksandrov <razor@xxxxxxxxxxxxx>
    Link: https://lore.kernel.org/r/20240227121128.608110-1-linma@xxxxxxxxxx
    Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index 1b71e5c582bbc..ef218e290dfba 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -4925,10 +4925,9 @@ static int rtnl_bridge_setlink(struct sk_buff *skb, struct nlmsghdr *nlh,
 	struct net *net = sock_net(skb->sk);
 	struct ifinfomsg *ifm;
 	struct net_device *dev;
-	struct nlattr *br_spec, *attr = NULL;
+	struct nlattr *br_spec, *attr, *br_flags_attr = NULL;
 	int rem, err = -EOPNOTSUPP;
 	u16 flags = 0;
-	bool have_flags = false;
 
 	if (nlmsg_len(nlh) < sizeof(*ifm))
 		return -EINVAL;
@@ -4946,11 +4945,11 @@ static int rtnl_bridge_setlink(struct sk_buff *skb, struct nlmsghdr *nlh,
 	br_spec = nlmsg_find_attr(nlh, sizeof(struct ifinfomsg), IFLA_AF_SPEC);
 	if (br_spec) {
 		nla_for_each_nested(attr, br_spec, rem) {
-			if (nla_type(attr) == IFLA_BRIDGE_FLAGS && !have_flags) {
+			if (nla_type(attr) == IFLA_BRIDGE_FLAGS && !br_flags_attr) {
 				if (nla_len(attr) < sizeof(flags))
 					return -EINVAL;
 
-				have_flags = true;
+				br_flags_attr = attr;
 				flags = nla_get_u16(attr);
 			}
 
@@ -4994,8 +4993,8 @@ static int rtnl_bridge_setlink(struct sk_buff *skb, struct nlmsghdr *nlh,
 		}
 	}
 
-	if (have_flags)
-		memcpy(nla_data(attr), &flags, sizeof(flags));
+	if (br_flags_attr)
+		memcpy(nla_data(br_flags_attr), &flags, sizeof(flags));
 out:
 	return err;
 }