| Message ID | 20180926203446.2004-5-casey.schaufler@intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | LSM: Support ptrace sidechannel access checks | expand |
On Wed, Sep 26, 2018 at 10:35 PM Casey Schaufler <casey.schaufler@intel.com> 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? > Signed-off-by: Casey Schaufler <casey.schaufler@intel.com> > --- > 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;
> -----Original Message----- > From: Jann Horn [mailto:jannh@google.com] > Sent: Wednesday, September 26, 2018 2:26 PM > To: Schaufler, Casey <casey.schaufler@intel.com> > Cc: Kernel Hardening <kernel-hardening@lists.openwall.com>; kernel list > <linux-kernel@vger.kernel.org>; linux-security-module <linux-security- > module@vger.kernel.org>; selinux@tycho.nsa.gov; Hansen, Dave > <dave.hansen@intel.com>; Dock, Deneen T <deneen.t.dock@intel.com>; > kristen@linux.intel.com; Arjan van de Ven <arjan@linux.intel.com> > Subject: Re: [PATCH v5 4/5] Capability: Complete PTRACE_MODE_SCHED > > On Wed, Sep 26, 2018 at 10:35 PM Casey Schaufler > <casey.schaufler@intel.com> 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? ns_capable() eventually gets you to an audit call. The audit code is going to do the locking. Fortunately, the preceding cap_issubset() is the check that we really need here. > > > Signed-off-by: Casey Schaufler <casey.schaufler@intel.com> > > --- > > 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? That can't be right, can it? Determining that we have PTRACE_MODE_SCHED at this point should result in -EPERM. I mucked up on the logic flow. The next revision will fix this. > 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;
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; if (ns_capable(child_cred->user_ns, CAP_SYS_PTRACE)) goto out; ret = -EPERM;