ptrace: do not audit capability check when outputing /proc/pid/stat

Reading /proc/pid/stat of another process checks if one has ptrace permissions
on that process.  If one does have permissions it outputs some data about the
process which might have security and attack implications.  If the current
task does not have ptrace permissions the read still works, but those fields
are filled with inocuous (0) values.  Since this check and a subsequent denial
is not a violation of the security policy we should not audit such denials.

This can be quite useful to removing ptrace broadly across a system without
flooding the logs when ps is run or something which harmlessly walks proc.

Signed-off-by: Eric Paris <eparis@redhat.com>
Acked-by: Serge E. Hallyn <serge.hallyn@canonical.com>

diff --git a/fs/proc/array.c b/fs/proc/array.c
index 3a1dafd..ddffd7a 100644 (file)
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -380,7 +380,7 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
 
        state = *get_task_state(task);
        vsize = eip = esp = 0;
-       permitted = ptrace_may_access(task, PTRACE_MODE_READ);
+       permitted = ptrace_may_access(task, PTRACE_MODE_READ | PTRACE_MODE_NOAUDIT);
        mm = get_task_mm(task);
        if (mm) {
                vsize = task_vsize(mm);

diff --git a/include/linux/ptrace.h b/include/linux/ptrace.h
index 800f113..a27e56c 100644 (file)
--- a/include/linux/ptrace.h
+++ b/include/linux/ptrace.h
@@ -127,8 +127,9 @@ extern void __ptrace_link(struct task_struct *child,
                          struct task_struct *new_parent);
 extern void __ptrace_unlink(struct task_struct *child);
 extern void exit_ptrace(struct task_struct *tracer);
-#define PTRACE_MODE_READ   1
-#define PTRACE_MODE_ATTACH 2
+#define PTRACE_MODE_READ       0x01
+#define PTRACE_MODE_ATTACH     0x02
+#define PTRACE_MODE_NOAUDIT    0x04
 /* Returns 0 on success, -errno on denial. */
 extern int __ptrace_may_access(struct task_struct *task, unsigned int mode);
 /* Returns true on success, false on denial. */

diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 210bbf0..c890ac9 100644 (file)
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -161,6 +161,14 @@ int ptrace_check_attach(struct task_struct *child, bool ignore_state)
        return ret;
 }
 
+static int ptrace_has_cap(struct user_namespace *ns, unsigned int mode)
+{
+       if (mode & PTRACE_MODE_NOAUDIT)
+               return has_ns_capability_noaudit(current, ns, CAP_SYS_PTRACE);
+       else
+               return has_ns_capability(current, ns, CAP_SYS_PTRACE);
+}
+
 int __ptrace_may_access(struct task_struct *task, unsigned int mode)
 {
        const struct cred *cred = current_cred(), *tcred;
@@ -187,7 +195,7 @@ int __ptrace_may_access(struct task_struct *task, unsigned int mode)
             cred->gid == tcred->sgid &&
             cred->gid == tcred->gid))
                goto ok;
-       if (ns_capable(tcred->user->user_ns, CAP_SYS_PTRACE))
+       if (ptrace_has_cap(tcred->user->user_ns, mode))
                goto ok;
        rcu_read_unlock();
        return -EPERM;
@@ -196,7 +204,7 @@ ok:
        smp_rmb();
        if (task->mm)
                dumpable = get_dumpable(task->mm);
-       if (!dumpable && !ns_capable(task_user_ns(task), CAP_SYS_PTRACE))
+       if (!dumpable  && !ptrace_has_cap(task_user_ns(task), mode))
                return -EPERM;
 
        return security_ptrace_access_check(task, mode);

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index c9605c4..14f94cd 100644 (file)
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -1809,7 +1809,7 @@ static int selinux_ptrace_access_check(struct task_struct *child,
        if (rc)
                return rc;
 
-       if (mode == PTRACE_MODE_READ) {
+       if (mode & PTRACE_MODE_READ) {
                u32 sid = current_sid();
                u32 csid = task_sid(child);
                return avc_has_perm(sid, csid, SECCLASS_FILE, FILE__READ, NULL);