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
Acked-by: Serge Hallyn
Acked-by: Casey Schaufler
Acked-by: Andrew G. Morgan
Acked-by: James Morris
Acked-by: Al Viro
---

include/linux/capability.h | 15 ++++++++++++-
include/linux/security.h | 39 ++++++++++++++++++++++-------------
kernel/capability.c | 21 ++++++++++++-------
kernel/ptrace.c | 5 ++--
mm/oom_kill.c | 6 ++++-
security/capability.c | 3 ++-
security/commoncap.c | 24 +++++++++++++++-------
security/root_plug.c | 3 ++-
security/security.c | 10 ++++++---
security/selinux/hooks.c | 25 ++++++++++++++++------
security/smack/smack_lsm.c | 49 +++++++++++++++++++++++++++++++-------------
11 files changed, 137 insertions(+), 63 deletions(-)


diff --git a/include/linux/capability.h b/include/linux/capability.h
index 0267384..9d1fe30 100644
--- a/include/linux/capability.h
+++ b/include/linux/capability.h
@@ -503,8 +503,19 @@ extern const kernel_cap_t __cap_init_eff_set;

kernel_cap_t cap_set_effective(const kernel_cap_t pE_new);

-int capable(int cap);
-int __capable(struct task_struct *t, int cap);
+/**
+ * has_capability - Determine if a task has a superior capability available
+ * @t: The task in question
+ * @cap: The capability to be tested for
+ *
+ * Return true if the specified task has the given superior capability
+ * currently in effect, false if not.
+ *
+ * Note that this does not set PF_SUPERPRIV on the task.
+ */
+#define has_capability(t, cap) (security_capable((t), (cap)) == 0)
+
+extern int capable(int cap);

#endif /* __KERNEL__ */

diff --git a/include/linux/security.h b/include/linux/security.h
index fd96e7f..80c4d00 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -46,8 +46,8 @@ struct audit_krule;
*/
extern int cap_capable(struct task_struct *tsk, int cap);
extern int cap_settime(struct timespec *ts, struct timezone *tz);
-extern int cap_ptrace(struct task_struct *parent, struct task_struct *child,
- unsigned int mode);
+extern int cap_ptrace_may_access(struct task_struct *child, unsigned int mode);
+extern int cap_ptrace_traceme(struct task_struct *parent);
extern int cap_capget(struct task_struct *target, kernel_cap_t *effective, kernel_cap_t *inheritable, kernel_cap_t *permitted);
extern int cap_capset_check(struct task_struct *target, kernel_cap_t *effective, kernel_cap_t *inheritable, kernel_cap_t *permitted);
extern void cap_capset_set(struct task_struct *target, kernel_cap_t *effective, kernel_cap_t *inheritable, kernel_cap_t *permitted);
@@ -1157,17 +1157,24 @@ static inline void security_free_mnt_opts(struct security_mnt_opts *opts)
* @alter contains the flag indicating whether changes are to be made.
* Return 0 if permission is granted.
*
- * @ptrace:
- * Check permission before allowing the @parent process to trace the
+ * @ptrace_may_access:
+ * Check permission before allowing the current process to trace the
* @child process.
* Security modules may also want to perform a process tracing check
* during an execve in the set_security or apply_creds hooks of
* binprm_security_ops if the process is being traced and its security
* attributes would be changed by the execve.
- * @parent contains the task_struct structure for parent process.
- * @child contains the task_struct structure for child process.
+ * @child contains the task_struct structure for the target process.
* @mode contains the PTRACE_MODE flags indicating the form of access.
* Return 0 if permission is granted.
+ * @ptrace_traceme:
+ * Check that the @parent process has sufficient permission to trace the
+ * current process before allowing the current process to present itself
+ * to the @parent process for tracing.
+ * The parent process will still have to undergo the ptrace_may_access
+ * checks before it is allowed to trace this one.
+ * @parent contains the task_struct structure for debugger process.
+ * Return 0 if permission is granted.
* @capget:
* Get the @effective, @inheritable, and @permitted capability sets for
* the @target process. The hook may also perform permission checking to
@@ -1287,8 +1294,8 @@ static inline void security_free_mnt_opts(struct security_mnt_opts *opts)
struct security_operations {
char name[SECURITY_NAME_MAX + 1];

- int (*ptrace) (struct task_struct *parent, struct task_struct *child,
- unsigned int mode);
+ int (*ptrace_may_access) (struct task_struct *child, unsigned int mode);
+ int (*ptrace_traceme) (struct task_struct *parent);
int (*capget) (struct task_struct *target,
kernel_cap_t *effective,
kernel_cap_t *inheritable, kernel_cap_t *permitted);
@@ -1560,8 +1567,8 @@ extern struct dentry *securityfs_create_dir(const char *name, struct dentry *par
extern void securityfs_remove(struct dentry *dentry);

/* Security operations */
-int security_ptrace(struct task_struct *parent, struct task_struct *child,
- unsigned int mode);
+int security_ptrace_may_access(struct task_struct *child, unsigned int mode);
+int security_ptrace_traceme(struct task_struct *parent);
int security_capget(struct task_struct *target,
kernel_cap_t *effective,
kernel_cap_t *inheritable,
@@ -1742,11 +1749,15 @@ static inline int security_init(void)
return 0;
}

-static inline int security_ptrace(struct task_struct *parent,
- struct task_struct *child,
- unsigned int mode)
+static inline int security_ptrace_may_access(struct task_struct *child,
+ unsigned int mode)
+{
+ return cap_ptrace_may_access(child, mode);
+}
+
+static inline int security_ptrace_traceme(struct task_struct *parent)
{
- return cap_ptrace(parent, child, mode);
+ return cap_ptrace_traceme(parent);
}

static inline int security_capget(struct task_struct *target,
diff --git a/kernel/capability.c b/kernel/capability.c
index 0101e84..33e51e7 100644
--- a/kernel/capability.c
+++ b/kernel/capability.c
@@ -486,17 +486,22 @@ asmlinkage long sys_capset(cap_user_header_t header, const cap_user_data_t data)
return ret;
}

-int __capable(struct task_struct *t, int cap)
+/**
+ * capable - Determine if the current task has a superior capability in effect
+ * @cap: The capability to be tested for
+ *
+ * Return true if the current task has the given superior capability currently
+ * available for use, false if not.
+ *
+ * This sets PF_SUPERPRIV on the task if the capability is available on the
+ * assumption that it's about to be used.
+ */
+int capable(int cap)
{
- if (security_capable(t, cap) == 0) {
- t->flags |= PF_SUPERPRIV;
+ if (has_capability(current, cap)) {
+ current->flags |= PF_SUPERPRIV;
return 1;
}
return 0;
}
-
-int capable(int cap)
-{
- return __capable(current, cap);
-}
EXPORT_SYMBOL(capable);
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 082b3fc..356699a 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -140,7 +140,7 @@ int __ptrace_may_access(struct task_struct *task, unsigned int mode)
if (!dumpable && !capable(CAP_SYS_PTRACE))
return -EPERM;

- return security_ptrace(current, task, mode);
+ return security_ptrace_may_access(task, mode);
}

bool ptrace_may_access(struct task_struct *task, unsigned int mode)
@@ -499,8 +499,7 @@ repeat:
goto repeat;
}

- ret = security_ptrace(current->parent, current,
- PTRACE_MODE_ATTACH);
+ ret = security_ptrace_traceme(current->parent);

/*
* Set the ptrace bit in the process ptrace flags.
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 8a5467e..64e5b4b 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -26,6 +26,7 @@
#include
#include
#include
+#include

int sysctl_panic_on_oom;
int sysctl_oom_kill_allocating_task;
@@ -128,7 +129,8 @@ unsigned long badness(struct task_struct *p, unsigned long uptime)
* Superuser processes are usually more important, so we make it
* less likely that we kill those.
*/
- if (__capable(p, CAP_SYS_ADMIN) || __capable(p, CAP_SYS_RESOURCE))
+ if (has_capability(p, CAP_SYS_ADMIN) ||
+ has_capability(p, CAP_SYS_RESOURCE))
points /= 4;

/*
@@ -137,7 +139,7 @@ unsigned long badness(struct task_struct *p, unsigned long uptime)
* tend to only have this flag set on applications they think
* of as important.
*/
- if (__capable(p, CAP_SYS_RAWIO))
+ if (has_capability(p, CAP_SYS_RAWIO))
points /= 4;

/*
diff --git a/security/capability.c b/security/capability.c
index 63d10da..2458748 100644
--- a/security/capability.c
+++ b/security/capability.c
@@ -811,7 +811,8 @@ struct security_operations default_security_ops = {

void security_fixup_ops(struct security_operations *ops)
{
- set_to_cap_if_null(ops, ptrace);
+ set_to_cap_if_null(ops, ptrace_may_access);
+ set_to_cap_if_null(ops, ptrace_traceme);
set_to_cap_if_null(ops, capget);
set_to_cap_if_null(ops, capset_check);
set_to_cap_if_null(ops, capset_set);
diff --git a/security/commoncap.c b/security/commoncap.c
index 4afbece..e4c4b3f 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -63,14 +63,24 @@ int cap_settime(struct timespec *ts, struct timezone *tz)
return 0;
}

-int cap_ptrace (struct task_struct *parent, struct task_struct *child,
- unsigned int mode)
+int cap_ptrace_may_access(struct task_struct *child, unsigned int mode)
{
/* Derived from arch/i386/kernel/ptrace.c:sys_ptrace. */
- if (!cap_issubset(child->cap_permitted, parent->cap_permitted) &&
- !__capable(parent, CAP_SYS_PTRACE))
- return -EPERM;
- return 0;
+ if (cap_issubset(child->cap_permitted, current->cap_permitted))
+ return 0;
+ if (capable(CAP_SYS_PTRACE))
+ return 0;
+ return -EPERM;
+}
+
+int cap_ptrace_traceme(struct task_struct *parent)
+{
+ /* Derived from arch/i386/kernel/ptrace.c:sys_ptrace. */
+ if (cap_issubset(current->cap_permitted, parent->cap_permitted))
+ return 0;
+ if (has_capability(parent, CAP_SYS_PTRACE))
+ return 0;
+ return -EPERM;
}

int cap_capget (struct task_struct *target, kernel_cap_t *effective,
@@ -534,7 +544,7 @@ int cap_task_post_setuid (uid_t old_ruid, uid_t old_euid, uid_t old_suid,
static inline int cap_safe_nice(struct task_struct *p)
{
if (!cap_issubset(p->cap_permitted, current->cap_permitted) &&
- !__capable(current, CAP_SYS_NICE))
+ !capable(CAP_SYS_NICE))
return -EPERM;
return 0;
}
diff --git a/security/root_plug.c b/security/root_plug.c
index be0ebec..c3f68b5 100644
--- a/security/root_plug.c
+++ b/security/root_plug.c
@@ -72,7 +72,8 @@ static int rootplug_bprm_check_security (struct linux_binprm *bprm)

static struct security_operations rootplug_security_ops = {
/* Use the capability functions for some of the hooks */
- .ptrace = cap_ptrace,
+ .ptrace_may_access = cap_ptrace_may_access,
+ .ptrace_traceme = cap_ptrace_traceme,
.capget = cap_capget,
.capset_check = cap_capset_check,
.capset_set = cap_capset_set,
diff --git a/security/security.c b/security/security.c
index ff70687..3a4b4f5 100644
--- a/security/security.c
+++ b/security/security.c
@@ -127,10 +127,14 @@ int register_security(struct security_operations *ops)

/* Security operations */

-int security_ptrace(struct task_struct *parent, struct task_struct *child,
- unsigned int mode)
+int security_ptrace_may_access(struct task_struct *child, unsigned int mode)
{
- return security_ops->ptrace(parent, child, mode);
+ return security_ops->ptrace_may_access(child, mode);
+}
+
+int security_ptrace_traceme(struct task_struct *parent)
+{
+ return security_ops->ptrace_traceme(parent);
}

int security_capget(struct task_struct *target,
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 3eae306..6b5790b 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -1739,24 +1739,34 @@ static inline u32 file_to_av(struct file *file)

/* Hook functions begin here. */

-static int selinux_ptrace(struct task_struct *parent,
- struct task_struct *child,
- unsigned int mode)
+static int selinux_ptrace_may_access(struct task_struct *child,
+ unsigned int mode)
{
int rc;

- rc = secondary_ops->ptrace(parent, child, mode);
+ rc = secondary_ops->ptrace_may_access(child, mode);
if (rc)
return rc;

if (mode == PTRACE_MODE_READ) {
- struct task_security_struct *tsec = parent->security;
+ struct task_security_struct *tsec = current->security;
struct task_security_struct *csec = child->security;
return avc_has_perm(tsec->sid, csec->sid,
SECCLASS_FILE, FILE__READ, NULL);
}

- return task_has_perm(parent, child, PROCESS__PTRACE);
+ return task_has_perm(current, child, PROCESS__PTRACE);
+}
+
+static int selinux_ptrace_traceme(struct task_struct *parent)
+{
+ int rc;
+
+ rc = secondary_ops->ptrace_traceme(parent);
+ if (rc)
+ return rc;
+
+ return task_has_perm(parent, current, PROCESS__PTRACE);
}

static int selinux_capget(struct task_struct *target, kernel_cap_t *effective,
@@ -5353,7 +5363,8 @@ static int selinux_key_getsecurity(struct key *key, char **_buffer)
static struct security_operations selinux_ops = {
.name = "selinux",

- .ptrace = selinux_ptrace,
+ .ptrace_may_access = selinux_ptrace_may_access,
+ .ptrace_traceme = selinux_ptrace_traceme,
.capget = selinux_capget,
.capset_check = selinux_capset_check,
.capset_set = selinux_capset_set,
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 @@ struct inode_smack *new_inode_smack(char *smack)
*/

/**
- * 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 @@ static int smack_file_send_sigiotask(struct task_struct *tsk,
*/
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 @@ static int smack_task_wait(struct task_struct *p)
* 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 @@ static int smack_setprocattr(struct task_struct *p, char *name,
{
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 @@ static int smack_setprocattr(struct task_struct *p, char *name,
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 @@ static void smack_release_secctx(char *secdata, u32 seclen)
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 @@ static __init int smack_init(void)
* all processes and objects when they are created.
*/
security_initcall(smack_init);
-

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