Commit 5cd9c58f authored by David Howells's avatar David Howells Committed by James Morris

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: default avatarDavid Howells <dhowells@redhat.com>
Acked-by: default avatarSerge Hallyn <serue@us.ibm.com>
Acked-by: default avatarCasey Schaufler <casey@schaufler-ca.com>
Acked-by: default avatarAndrew G. Morgan <morgan@kernel.org>
Acked-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
Signed-off-by: default avatarJames Morris <jmorris@namei.org>
parent 8d0968ab
......@@ -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__ */
......
......@@ -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 *child)
{
return cap_ptrace(parent, child, mode);
return cap_ptrace_traceme(parent);
}
static inline int security_capget(struct task_struct *target,
......
......@@ -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);
......@@ -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 @@ int ptrace_traceme(void)
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.
......
......@@ -26,6 +26,7 @@
#include <linux/module.h>
#include <linux/notifier.h>
#include <linux/memcontrol.h>
#include <linux/security.h>
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;
/*
......
......@@ -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);
......
......@@ -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;
}
......
......@@ -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,
......
......@@ -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,
......
......@@ -1738,24 +1738,34 @@ 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,
......@@ -5346,7 +5356,8 @@ 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,
......
......@@ -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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