Since seccomp transitions between threads requires updates to the
no_new_privs flag to be atomic, changes must be atomic. This moves the nnp
flag into the seccomp field as a separate unsigned long for atomic access.
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Acked-by: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
---
fs/exec.c | 4 ++--
include/linux/sched.h | 13 ++++++++++---
include/linux/seccomp.h | 8 +++++++-
kernel/seccomp.c | 2 +-
kernel/sys.c | 4 ++--
security/apparmor/domain.c | 4 ++--
6 files changed, 24 insertions(+), 11 deletions(-)
diff --git a/fs/exec.c b/fs/exec.c
index 238b7aa26f68..614fcb993739 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1233,7 +1233,7 @@ static void check_unsafe_exec(struct linux_binprm *bprm)
* This isn't strictly necessary, but it makes it harder for LSMs to
* mess up.
*/
- if (current->no_new_privs)
+ if (task_no_new_privs(current))
bprm->unsafe |= LSM_UNSAFE_NO_NEW_PRIVS;
t = p;
@@ -1271,7 +1271,7 @@ int prepare_binprm(struct linux_binprm *bprm)
bprm->cred->egid = current_egid();
if (!(bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID) &&
- !current->no_new_privs &&
+ !task_no_new_privs(current) &&
kuid_has_mapping(bprm->cred->user_ns, inode->i_uid) &&
kgid_has_mapping(bprm->cred->user_ns, inode->i_gid)) {
/* Set-uid? */
diff --git a/include/linux/sched.h b/include/linux/sched.h
index ea74596014a2..50b41affb7b1 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1307,9 +1307,6 @@ struct task_struct {
* execve */
unsigned in_iowait:1;
- /* task may not gain privileges */
- unsigned no_new_privs:1;
-
/* Revert to default priority/policy when forking */
unsigned sched_reset_on_fork:1;
unsigned sched_contributes_to_load:1;
@@ -2525,6 +2522,16 @@ static inline void task_unlock(struct task_struct *p)
spin_unlock(&p->alloc_lock);
}
+static inline bool task_no_new_privs(struct task_struct *p)
+{
+ return test_bit(SECCOMP_FLAG_NO_NEW_PRIVS, &p->seccomp.flags);
+}
+
+static inline void task_set_no_new_privs(struct task_struct *p)
+{
+ set_bit(SECCOMP_FLAG_NO_NEW_PRIVS, &p->seccomp.flags);
+}
+
extern struct sighand_struct *__lock_task_sighand(struct task_struct *tsk,
unsigned long *flags);
diff --git a/include/linux/seccomp.h b/include/linux/seccomp.h
index 9ff98b4bfe2e..6a5e2d0ec912 100644
--- a/include/linux/seccomp.h
+++ b/include/linux/seccomp.h
@@ -3,6 +3,8 @@
#include <uapi/linux/seccomp.h>
+#define SECCOMP_FLAG_NO_NEW_PRIVS 0 /* task may not gain privs */
+
#ifdef CONFIG_SECCOMP
#include <linux/thread_info.h>
@@ -16,6 +18,7 @@ struct seccomp_filter;
* system calls available to a process.
* @filter: must always point to a valid seccomp-filter or NULL as it is
* accessed without locking during system call entry.
+ * @flags: flags under task->sighand->siglock lock
*
* @filter must only be accessed from the context of current as there
* is no read locking.
@@ -23,6 +26,7 @@ struct seccomp_filter;
struct seccomp {
int mode;
struct seccomp_filter *filter;
+ unsigned long flags;
};
extern int __secure_computing(int);
@@ -51,7 +55,9 @@ static inline int seccomp_mode(struct seccomp *s)
#include <linux/errno.h>
-struct seccomp { };
+struct seccomp {
+ unsigned long flags;
+};
struct seccomp_filter { };
static inline int secure_computing(int this_syscall) { return 0; }
diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index 33655302b658..7ec99b99e400 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -219,7 +219,7 @@ static struct seccomp_filter *seccomp_prepare_filter(struct sock_fprog *fprog)
* This avoids scenarios where unprivileged tasks can affect the
* behavior of privileged children.
*/
- if (!current->no_new_privs &&
+ if (!task_no_new_privs(current) &&
security_capable_noaudit(current_cred(), current_user_ns(),
CAP_SYS_ADMIN) != 0)
return ERR_PTR(-EACCES);
diff --git a/kernel/sys.c b/kernel/sys.c
index 66a751ebf9d9..ce8129192a26 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1990,12 +1990,12 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
if (arg2 != 1 || arg3 || arg4 || arg5)
return -EINVAL;
- current->no_new_privs = 1;
+ task_set_no_new_privs(current);
break;
case PR_GET_NO_NEW_PRIVS:
if (arg2 || arg3 || arg4 || arg5)
return -EINVAL;
- return current->no_new_privs ? 1 : 0;
+ return task_no_new_privs(current) ? 1 : 0;
case PR_GET_THP_DISABLE:
if (arg2 || arg3 || arg4 || arg5)
return -EINVAL;
diff --git a/security/apparmor/domain.c b/security/apparmor/domain.c
index 452567d3a08e..d97cba3e3849 100644
--- a/security/apparmor/domain.c
+++ b/security/apparmor/domain.c
@@ -621,7 +621,7 @@ int aa_change_hat(const char *hats[], int count, u64 token, bool permtest)
* There is no exception for unconfined as change_hat is not
* available.
*/
- if (current->no_new_privs)
+ if (task_no_new_privs(current))
return -EPERM;
/* released below */
@@ -776,7 +776,7 @@ int aa_change_profile(const char *ns_name, const char *hname, bool onexec,
* no_new_privs is set because this aways results in a reduction
* of permissions.
*/
- if (current->no_new_privs && !unconfined(profile)) {
+ if (task_no_new_privs(current) && !unconfined(profile)) {
put_cred(cred);
return -EPERM;
}
--
1.7.9.5
