security: Fix setting of PF_SUPERPRIV by __capable()
Fix the setting of PF_SUPERPRIV by __capable() as it could corrupt the flags
the target process if that is not the current process and it is trying to
change its own flags in a different way at the same time.
__capable() is using neither atomic ops nor locking to protect t->flags. This
patch removes __capable() and introduces has_capability() that doesn't set
PF_SUPERPRIV on the process being queried.
This patch further splits security_ptrace() in two:
(1) security_ptrace_may_access(). This passes judgement on whether one
process may access another only (PTRACE_MODE_ATTACH for ptrace() and
PTRACE_MODE_READ for /proc), and takes a pointer to the child process.
current is the parent.
(2) security_ptrace_traceme(). This passes judgement on PTRACE_TRACEME only,
and takes only a pointer to the parent process. current is the child.
In Smack and commoncap, this uses has_capability() to determine whether
the parent will be permitted to use PTRACE_ATTACH if normal checks fail.
This does not set PF_SUPERPRIV.
Two of the instances of __capable() actually only act on current, and so have
been changed to calls to capable().
Of the places that were using __capable():
(1) The OOM killer calls __capable() thrice when weighing the killability of a
process. All of these now use has_capability().
(2) cap_ptrace() and smack_ptrace() were using __capable() to check to see
whether the parent was allowed to trace any process. As mentioned above,
these have been split. For PTRACE_ATTACH and /proc, capable() is now
used, and for PTRACE_TRACEME, has_capability() is used.
(3) cap_safe_nice() only ever saw current, so now uses capable().
(4) smack_setprocattr() rejected accesses to tasks other than current just
after calling __capable(), so the order of these two tests have been
switched and capable() is used instead.
(5) In smack_file_send_sigiotask(), we need to allow privileged processes to
receive SIGIO on files they're manipulating.
(6) In smack_task_wait(), we let a process wait for a privileged process,
whether or not the process doing the waiting is privileged.
I've tested this with the LTP SELinux and syscalls testscripts.
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Acked-by: Casey Schaufler <casey@schaufler-ca.com>
Acked-by: Andrew G. Morgan <morgan@kernel.org>
Acked-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: James Morris <jmorris@namei.org>
diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index 1b40e55..87d7541 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -87,27 +87,46 @@
*/
/**
- * smack_ptrace - Smack approval on ptrace
- * @ptp: parent task pointer
+ * smack_ptrace_may_access - Smack approval on PTRACE_ATTACH
* @ctp: child task pointer
*
* Returns 0 if access is OK, an error code otherwise
*
* Do the capability checks, and require read and write.
*/
-static int smack_ptrace(struct task_struct *ptp, struct task_struct *ctp,
- unsigned int mode)
+static int smack_ptrace_may_access(struct task_struct *ctp, unsigned int mode)
{
int rc;
- rc = cap_ptrace(ptp, ctp, mode);
+ rc = cap_ptrace_may_access(ctp, mode);
if (rc != 0)
return rc;
- rc = smk_access(ptp->security, ctp->security, MAY_READWRITE);
- if (rc != 0 && __capable(ptp, CAP_MAC_OVERRIDE))
+ rc = smk_access(current->security, ctp->security, MAY_READWRITE);
+ if (rc != 0 && capable(CAP_MAC_OVERRIDE))
return 0;
+ return rc;
+}
+/**
+ * smack_ptrace_traceme - Smack approval on PTRACE_TRACEME
+ * @ptp: parent task pointer
+ *
+ * Returns 0 if access is OK, an error code otherwise
+ *
+ * Do the capability checks, and require read and write.
+ */
+static int smack_ptrace_traceme(struct task_struct *ptp)
+{
+ int rc;
+
+ rc = cap_ptrace_traceme(ptp);
+ if (rc != 0)
+ return rc;
+
+ rc = smk_access(ptp->security, current->security, MAY_READWRITE);
+ if (rc != 0 && has_capability(ptp, CAP_MAC_OVERRIDE))
+ return 0;
return rc;
}
@@ -923,7 +942,7 @@
*/
file = container_of(fown, struct file, f_owner);
rc = smk_access(file->f_security, tsk->security, MAY_WRITE);
- if (rc != 0 && __capable(tsk, CAP_MAC_OVERRIDE))
+ if (rc != 0 && has_capability(tsk, CAP_MAC_OVERRIDE))
return 0;
return rc;
}
@@ -1164,12 +1183,12 @@
* account for the smack labels having gotten to
* be different in the first place.
*
- * This breaks the strict subjet/object access
+ * This breaks the strict subject/object access
* control ideal, taking the object's privilege
* state into account in the decision as well as
* the smack value.
*/
- if (capable(CAP_MAC_OVERRIDE) || __capable(p, CAP_MAC_OVERRIDE))
+ if (capable(CAP_MAC_OVERRIDE) || has_capability(p, CAP_MAC_OVERRIDE))
return 0;
return rc;
@@ -2016,9 +2035,6 @@
{
char *newsmack;
- if (!__capable(p, CAP_MAC_ADMIN))
- return -EPERM;
-
/*
* Changing another process' Smack value is too dangerous
* and supports no sane use case.
@@ -2026,6 +2042,9 @@
if (p != current)
return -EPERM;
+ if (!capable(CAP_MAC_ADMIN))
+ return -EPERM;
+
if (value == NULL || size == 0 || size >= SMK_LABELLEN)
return -EINVAL;
@@ -2552,7 +2571,8 @@
struct security_operations smack_ops = {
.name = "smack",
- .ptrace = smack_ptrace,
+ .ptrace_may_access = smack_ptrace_may_access,
+ .ptrace_traceme = smack_ptrace_traceme,
.capget = cap_capget,
.capset_check = cap_capset_check,
.capset_set = cap_capset_set,
@@ -2729,4 +2749,3 @@
* all processes and objects when they are created.
*/
security_initcall(smack_init);
-