CVE-2024-27414

In the Linux kernel, the following vulnerability has been resolved:

rtnetlink: fix error logic of IFLABRIDGEFLAGS writing back

In the commit d73ef2d69c0d ("rtnetlink: let rtnlbridgesetlink checks IFLABRIDGEMODE 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 IFLABRIDGEMODE 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 (haveflags) memcpy(nladata(attr), &flags, sizeof(flags)); // attr should point to IFLABRIDGEFLAGS NLA !!!

Before the mentioned commit, the attr is granted to be IFLABRIDGEFLAGS. 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 IFLABRIDGEFLAGS and uses it to resolve the mentioned error logic.