On Fri, 05 Feb 2021 11:36:30 +1100 NeilBrown [off-list ref] wrote:

A recent change to seq_file broke some users which were using seq_file
in a non-"standard" way ...  though the "standard" isn't documented, so
they can be excused.  The result is a possible leak - of memory in one
case, of references to a 'transport' in the other.

These three patches:
 1/ document and explain the problem
 2/ fix the problem user in x86
 3/ fix the problem user in net/sctp

1f4aace60b0e ("fs/seq_file.c: simplify seq_file iteration code and
interface") was August 2018, so I don't think "recent" applies here?

I didn't look closely, but it appears that the sctp procfs file is
world-readable.  So we gave unprivileged userspace the ability to leak
kernel memory?

So I'm thinking that we aim for 5.12-rc1 on all three patches with a cc:stable?