From: Ondrej Mosnacek omosnace@redhat.com
commit 08ef1af4de5fe7de9c6d69f1e22e51b66e385d9b upstream.
Currently, the lockdown state is queried unconditionally, even though its result is used only if the PERF_SAMPLE_REGS_INTR bit is set in attr.sample_type. While that doesn't matter in case of the Lockdown LSM, it causes trouble with the SELinux's lockdown hook implementation.
SELinux implements the locked_down hook with a check whether the current task's type has the corresponding "lockdown" class permission ("integrity" or "confidentiality") allowed in the policy. This means that calling the hook when the access control decision would be ignored generates a bogus permission check and audit record.
Fix this by checking sample_type first and only calling the hook when its result would be honored.
Fixes: b0c8fdc7fdb7 ("lockdown: Lock down perf when in confidentiality mode") Signed-off-by: Ondrej Mosnacek omosnace@redhat.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Reviewed-by: Paul Moore paul@paul-moore.com Link: https://lkml.kernel.org/r/20210224215628.192519-1-omosnace@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/events/core.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-)
--- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -10953,12 +10953,12 @@ SYSCALL_DEFINE5(perf_event_open, perf_paranoid_kernel() && !capable(CAP_SYS_ADMIN)) return -EACCES;
- err = security_locked_down(LOCKDOWN_PERF); - if (err && (attr.sample_type & PERF_SAMPLE_REGS_INTR)) - /* REGS_INTR can leak data, lockdown must prevent this */ - return err; - - err = 0; + /* REGS_INTR can leak data, lockdown must prevent this */ + if (attr.sample_type & PERF_SAMPLE_REGS_INTR) { + err = security_locked_down(LOCKDOWN_PERF); + if (err) + return err; + }
/* * In cgroup mode, the pid argument is used to pass the fd