[PATCH v5 4/5] Capability: Complete PTRACE_MODE_SCHED
From: jannh@google.com (Jann Horn)
Date: 2018-09-26 21:26:37
Also in:
lkml, selinux
On Wed, Sep 26, 2018 at 10:35 PM Casey Schaufler [off-list ref] wrote:
Allow a complete ptrace access check with mode PTRACE_MODE_SCHED. Disable the inappropriate privilege check in the capability code that does incompatible locking.
What's that locking you're talking about?
quoted hunk ↗ jump to hunk
Signed-off-by: Casey Schaufler <redacted> --- kernel/ptrace.c | 2 -- security/commoncap.c | 2 ++ 2 files changed, 2 insertions(+), 2 deletions(-)diff --git a/kernel/ptrace.c b/kernel/ptrace.c index 99cfddde6a55..0b6a9df51c3b 100644 --- a/kernel/ptrace.c +++ b/kernel/ptrace.c@@ -331,8 +331,6 @@ static int __ptrace_may_access(struct task_struct *task, unsigned int mode) !ptrace_has_cap(mm->user_ns, mode))) return -EPERM; - if (mode & PTRACE_MODE_SCHED) - return 0; return security_ptrace_access_check(task, mode); }diff --git a/security/commoncap.c b/security/commoncap.c index 2e489d6a3ac8..e77457110d05 100644 --- a/security/commoncap.c +++ b/security/commoncap.c@@ -152,6 +152,8 @@ int cap_ptrace_access_check(struct task_struct *child, unsigned int mode) if (cred->user_ns == child_cred->user_ns && cap_issubset(child_cred->cap_permitted, *caller_caps)) goto out; + if (mode & PTRACE_MODE_SCHED) + goto out;
So for PTRACE_MODE_SCHED, this function always returns 0, right? If that's intentional, perhaps you should instead just put "if (mode & PTRACE_MODE_SCHED) return 0;" at the start of the function, to avoid taking the RCU read lock in this case.
if (ns_capable(child_cred->user_ns, CAP_SYS_PTRACE))
goto out;
ret = -EPERM;