On Wed, Aug 12, 2026 at 10:59 AM Serge E. Hallyn <[email protected]> wrote: > On Mon, Aug 10, 2026 at 03:41:54PM -0400, Paul Moore wrote: > > On Aug 6, 2026 Jann Horn <[email protected]> wrote: > > > > > > The `cred` field in task_struct is currently marked as __rcu, but that's > > > not true: It can point to credentials from access_override_creds(), which > > > do not get freed with RCU delay. > > > > > > What actually protects task_struct::cred is that accessing it is only > > > permitted for the current task (except for setting up a child during > > > fork() > > > or tearing down a dead process). > > > (There is currently code in Smack that violates this rule, but that's a > > > bug > > > and causes UAF, I have sent a separate fix for that.) > > > > > > Clarify this, remove the __rcu marker, and remove RCU helpers from all > > > accesses to this field. > > > > > > Signed-off-by: Jann Horn <[email protected]> > > > --- > > > For context: > > > There have been at least two UAFs of struct cred that I'm aware of, both > > > caused by wrong use of task_struct::cred: > > > > > > - https://git.kernel.org/linus/a3727a8bac0a9e77c70820655fd8715523ba3db7 > > > - > > > https://lore.kernel.org/all/[email protected]/ > > > --- > > > include/linux/cred.h | 17 +++++++++++------ > > > include/linux/sched.h | 8 ++++++-- > > > kernel/auditsc.c | 5 +++-- > > > kernel/cred.c | 2 +- > > > security/lsm_init.c | 2 +- > > > 5 files changed, 22 insertions(+), 12 deletions(-) > > > > This looks good to me, with one small nit below, but as we are at -rc7 > > I think this is best kept until after the upcoming merge window so it > > has more than a few days in linux-next. I'm going to merge this into > > lsm/dev-staging with the expectation of merging it into lsm/dev after > > the upcoming merge window closes. If anyone wishes to object to this > > patch or add their own review/ACK/test tag before then, please do. > > > > Thanks Jann. > > > > Thanks. FWIW I did also look at this closely. > > Reviewed-by: Serge Hallyn <[email protected]>
Updated, thanks. -- paul-moore.com
