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Subject[resend][PATCH 3/4] move cred_guard_mutex from task_struct to signal_struct
Date
Changelog
o since v1
- function comment also change current->cred_guard_mutex to
current->signal->cred_guard_mutex.

---------------------------------------------------------------------------
Oleg Nesterov pointed out we have to prevent multiple-threads-inside-exec
itself and we can reuse ->cred_guard_mutex for it. Yes, concurrent
execve() has no worth.
Let's move ->cred_guard_mutex from task_struct to signal_struct. It
naturally prevent multiple-threads-inside-exec.

Cc: stable@kernel.org
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
---
fs/exec.c | 10 +++++-----
fs/proc/base.c | 8 ++++----
include/linux/init_task.h | 4 ++--
include/linux/sched.h | 7 ++++---
include/linux/tracehook.h | 2 +-
kernel/cred.c | 4 +---
kernel/fork.c | 2 ++
kernel/ptrace.c | 4 ++--
8 files changed, 21 insertions(+), 20 deletions(-)
diff --git a/fs/exec.c b/fs/exec.c
index 6d2b6f9..94dabd2 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1078,14 +1078,14 @@ EXPORT_SYMBOL(setup_new_exec);
*/
int prepare_bprm_creds(struct linux_binprm *bprm)
{
- if (mutex_lock_interruptible(&current->cred_guard_mutex))
+ if (mutex_lock_interruptible(&current->signal->cred_guard_mutex))
return -ERESTARTNOINTR;

bprm->cred = prepare_exec_creds();
if (likely(bprm->cred))
return 0;

- mutex_unlock(&current->cred_guard_mutex);
+ mutex_unlock(&current->signal->cred_guard_mutex);
return -ENOMEM;
}

@@ -1093,7 +1093,7 @@ void free_bprm(struct linux_binprm *bprm)
{
free_arg_pages(bprm);
if (bprm->cred) {
- mutex_unlock(&current->cred_guard_mutex);
+ mutex_unlock(&current->signal->cred_guard_mutex);
abort_creds(bprm->cred);
}
kfree(bprm);
@@ -1114,13 +1114,13 @@ void install_exec_creds(struct linux_binprm *bprm)
* credentials; any time after this it may be unlocked.
*/
security_bprm_committed_creds(bprm);
- mutex_unlock(&current->cred_guard_mutex);
+ mutex_unlock(&current->signal->cred_guard_mutex);
}
EXPORT_SYMBOL(install_exec_creds);

/*
* determine how safe it is to execute the proposed program
- * - the caller must hold current->cred_guard_mutex to protect against
+ * - the caller must hold ->cred_guard_mutex to protect against
* PTRACE_ATTACH
*/
int check_unsafe_exec(struct linux_binprm *bprm)
diff --git a/fs/proc/base.c b/fs/proc/base.c
index 0d2ce21..d3ea8b0 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -226,7 +226,7 @@ struct mm_struct *mm_for_maps(struct task_struct *task)
{
struct mm_struct *mm;

- if (mutex_lock_killable(&task->cred_guard_mutex))
+ if (mutex_lock_killable(&task->signal->cred_guard_mutex))
return NULL;

mm = get_task_mm(task);
@@ -235,7 +235,7 @@ struct mm_struct *mm_for_maps(struct task_struct *task)
mmput(mm);
mm = NULL;
}
- mutex_unlock(&task->cred_guard_mutex);
+ mutex_unlock(&task->signal->cred_guard_mutex);

return mm;
}
@@ -2277,14 +2277,14 @@ static ssize_t proc_pid_attr_write(struct file * file, const char __user * buf,
goto out_free;

/* Guard against adverse ptrace interaction */
- length = mutex_lock_interruptible(&task->cred_guard_mutex);
+ length = mutex_lock_interruptible(&task->signal->cred_guard_mutex);
if (length < 0)
goto out_free;

length = security_setprocattr(task,
(char*)file->f_path.dentry->d_name.name,
(void*)page, count);
- mutex_unlock(&task->cred_guard_mutex);
+ mutex_unlock(&task->signal->cred_guard_mutex);
out_free:
free_page((unsigned long) page);
out:
diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index 2fea6c8..1f8c06c 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -29,6 +29,8 @@ extern struct fs_struct init_fs;
.running = 0, \
.lock = __SPIN_LOCK_UNLOCKED(sig.cputimer.lock), \
}, \
+ .cred_guard_mutex = \
+ __MUTEX_INITIALIZER(sig.cred_guard_mutex), \
}

extern struct nsproxy init_nsproxy;
@@ -145,8 +147,6 @@ extern struct cred init_cred;
.group_leader = &tsk, \
RCU_INIT_POINTER(.real_cred, &init_cred), \
RCU_INIT_POINTER(.cred, &init_cred), \
- .cred_guard_mutex = \
- __MUTEX_INITIALIZER(tsk.cred_guard_mutex), \
.comm = "swapper", \
.thread = INIT_THREAD, \
.fs = &init_fs, \
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 74ed859..ac65605 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -626,6 +626,10 @@ struct signal_struct {

int oom_adj; /* OOM kill score adjustment (bit shift) */
long oom_score_adj; /* OOM kill score adjustment */
+
+ struct mutex cred_guard_mutex; /* guard against foreign influences on
+ * credential calculations
+ * (notably. ptrace) */
};

/* Context switch must be unlocked if interrupts are to be enabled */
@@ -1305,9 +1309,6 @@ struct task_struct {
* credentials (COW) */
const struct cred __rcu *cred; /* effective (overridable) subjective task
* credentials (COW) */
- struct mutex cred_guard_mutex; /* guard against foreign influences on
- * credential calculations
- * (notably. ptrace) */
struct cred *replacement_session_keyring; /* for KEYCTL_SESSION_TO_PARENT */

char comm[TASK_COMM_LEN]; /* executable name excluding path
diff --git a/include/linux/tracehook.h b/include/linux/tracehook.h
index 10db010..3a2e66d 100644
--- a/include/linux/tracehook.h
+++ b/include/linux/tracehook.h
@@ -150,7 +150,7 @@ static inline void tracehook_report_syscall_exit(struct pt_regs *regs, int step)
*
* Return %LSM_UNSAFE_* bits applied to an exec because of tracing.
*
- * @task->cred_guard_mutex is held by the caller through the do_execve().
+ * @task->signal->cred_guard_mutex is held by the caller through the do_execve().
*/
static inline int tracehook_unsafe_exec(struct task_struct *task)
{
diff --git a/kernel/cred.c b/kernel/cred.c
index 9a3e226..6a1aa00 100644
--- a/kernel/cred.c
+++ b/kernel/cred.c
@@ -325,7 +325,7 @@ EXPORT_SYMBOL(prepare_creds);

/*
* Prepare credentials for current to perform an execve()
- * - The caller must hold current->cred_guard_mutex
+ * - The caller must hold ->cred_guard_mutex
*/
struct cred *prepare_exec_creds(void)
{
@@ -384,8 +384,6 @@ int copy_creds(struct task_struct *p, unsigned long clone_flags)
struct cred *new;
int ret;

- mutex_init(&p->cred_guard_mutex);
-
if (
#ifdef CONFIG_KEYS
!p->cred->thread_keyring &&
diff --git a/kernel/fork.c b/kernel/fork.c
index c445f8c..8c09cf9 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -904,6 +904,8 @@ static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
sig->oom_adj = current->signal->oom_adj;
sig->oom_score_adj = current->signal->oom_score_adj;

+ mutex_init(&sig->cred_guard_mutex);
+
return 0;
}

diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index f34d798..ac5013a 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -181,7 +181,7 @@ int ptrace_attach(struct task_struct *task)
* under ptrace.
*/
retval = -ERESTARTNOINTR;
- if (mutex_lock_interruptible(&task->cred_guard_mutex))
+ if (mutex_lock_interruptible(&task->signal->cred_guard_mutex))
goto out;

task_lock(task);
@@ -208,7 +208,7 @@ int ptrace_attach(struct task_struct *task)
unlock_tasklist:
write_unlock_irq(&tasklist_lock);
unlock_creds:
- mutex_unlock(&task->cred_guard_mutex);
+ mutex_unlock(&task->signal->cred_guard_mutex);
out:
return retval;
}
--
1.6.5.2




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