In the Linux kernel, the following vulnerability has been resolved:
net: ipv6: flowlabel: defer exclusive option free until RCU teardown
ip6fl_seq_show() walks the global flowlabel hash under the seq-file
RCU read-side lock and prints fl->opt->opt_nflen when an option block
is present.
Exclusive flowlabels currently free fl->opt as soon as fl->users
drops to zero in fl_release(). However, the surrounding
struct ip6_flowlabel remains visible in the global hash table until
later garbage collection removes it and fl_free_rcu() finally tears it
down.
A concurrent /proc/net/ip6_flowlabel reader can therefore race that
early kfree() and dereference freed option state, triggering a crash
in ip6fl_seq_show().
Fix this by keeping fl->opt alive until fl_free_rcu(). That matches
the lifetime already required for the enclosing flowlabel while readers
can still reach it under RCU.