[PATCH 3.16 188/192] sched: move no_new_privs into new atomic flags

Ben Hutchings
2017-10-09T14:04:52Z

From: Kees Cook <keescook@chromium.org>

commit 1d4457f99928a968767f6405b4a1f50845aa15fd upstream.

Since seccomp transitions between threads requires updates to the
no_new_privs flag to be atomic, the flag must be part of an atomic flag
set. This moves the nnp flag into a separate task field, and introduces
accessors.

Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Andy Lutomirski <luto@amacapital.net>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
fs/exec.c | 4 ++--
include/linux/sched.h | 18 +++++++++++++++---
kernel/seccomp.c | 2 +-
kernel/sys.c | 4 ++--
security/apparmor/domain.c | 4 ++--
5 files changed, 22 insertions(+), 10 deletions(-)

--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1269,7 +1269,7 @@ static void check_unsafe_exec(struct lin
* 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;
@@ -1303,7 +1303,7 @@ static void bprm_fill_uid(struct linux_b
if (bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID)
return;

- if (current->no_new_privs)
+ if (task_no_new_privs(current))
return;

inode = file_inode(bprm->file);
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1317,13 +1317,12 @@ 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;

+ unsigned long atomic_flags; /* Flags needing atomic access. */
+
pid_t pid;
pid_t tgid;

@@ -1979,6 +1978,19 @@ static inline void memalloc_noio_restore
current->flags = (current->flags & ~PF_MEMALLOC_NOIO) | flags;
}

+/* Per-process atomic flags. */
+#define PFA_NO_NEW_PRIVS 0x00000001 /* May not gain new privileges. */
+
+static inline bool task_no_new_privs(struct task_struct *p)
+{
+ return test_bit(PFA_NO_NEW_PRIVS, &p->atomic_flags);
+}
+
+static inline void task_set_no_new_privs(struct task_struct *p)
+{
+ set_bit(PFA_NO_NEW_PRIVS, &p->atomic_flags);
+}
+
/*
* task->jobctl flags
*/
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -224,7 +224,7 @@ static long seccomp_attach_filter(struct
* 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 -EACCES;
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1989,12 +1989,12 @@ SYSCALL_DEFINE5(prctl, int, option, unsi
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;
--- a/security/apparmor/domain.c
+++ b/security/apparmor/domain.c
@@ -621,7 +621,7 @@ int aa_change_hat(const char *hats[], in
* 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 */
@@ -778,7 +778,7 @@ int aa_change_profile(const char *ns_nam
* 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;
}