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Message-ID: <20120113220028.4ba7cead@Gantu.yeoh.info>
Date: Fri, 13 Jan 2012 22:00:28 +1030
From: Christopher Yeoh <cyeoh@....ibm.com>
To: linux-kernel@...r.kernel.org, Oleg Nesterov <oleg@...hat.com>,
Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
David Howells <dhowells@...hat.com>
Subject: [PATCH] Fix race in process_vm_rw_core
Hi Linus,
Below is a patch which fixes the race in process_vm_core found by
Oleg (http://article.gmane.org/gmane.linux.kernel/1235667/).
It consolidates some code with mm_for_maps since what they do is almost
identical.
Oleg - I've kept the breakout of ptrace_may_attach and get_task_mm to
preserve only having to take the task lock once. I see some performance
difference with a microbenchmark but haven't had a chance to test with
some HPC benchmarks yet so for the moment I'd like to leave it in. At
this stage I think its more important to get the race fixed and I'm at
Linux.conf.au all next week. I'll send a patch out for the
rw_copy_check_uvector cleanup after I get back from LCA.
Regards,
Chris
--
cyeoh@...ibm.com
Signed-off-by: Chris Yeoh <yeohc@....ibm.com>
Cc: stable@...r.kernel.org
diff --git a/fs/proc/base.c b/fs/proc/base.c
index 851ba3d..094d650 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -254,22 +254,7 @@ static struct mm_struct *check_mem_permission(struct task_struct *task)
struct mm_struct *mm_for_maps(struct task_struct *task)
{
- struct mm_struct *mm;
- int err;
-
- err = mutex_lock_killable(&task->signal->cred_guard_mutex);
- if (err)
- return ERR_PTR(err);
-
- mm = get_task_mm(task);
- if (mm && mm != current->mm &&
- !ptrace_may_access(task, PTRACE_MODE_READ)) {
- mmput(mm);
- mm = ERR_PTR(-EACCES);
- }
- mutex_unlock(&task->signal->cred_guard_mutex);
-
- return mm;
+ return get_check_task_mm(task, PTRACE_MODE_READ);
}
static int proc_pid_cmdline(struct task_struct *task, char * buffer)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 1c4f3e9..8a64cae 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2235,6 +2235,10 @@ static inline void mmdrop(struct mm_struct * mm)
extern void mmput(struct mm_struct *);
/* Grab a reference to a task's mm, if it is not already going away */
extern struct mm_struct *get_task_mm(struct task_struct *task);
+/* Grab a reference to a task's mm, if it is not already going away
+ and ptrace_may_access with the mode parameter passed to it succeeds */
+extern struct mm_struct *get_check_task_mm(struct task_struct *task,
+ unsigned int mode);
/* Remove the current tasks stale references to the old mm_struct */
extern void mm_release(struct task_struct *, struct mm_struct *);
/* Allocate a new mm structure and copy contents from tsk->mm */
diff --git a/kernel/fork.c b/kernel/fork.c
index da4a6a1..9688fb0 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -644,6 +644,37 @@ struct mm_struct *get_task_mm(struct task_struct *task)
}
EXPORT_SYMBOL_GPL(get_task_mm);
+struct mm_struct *get_check_task_mm(struct task_struct *task, unsigned int mode)
+{
+ struct mm_struct *mm;
+ int err;
+
+ err = mutex_lock_killable(&task->signal->cred_guard_mutex);
+ if (err)
+ return ERR_PTR(err);
+
+ task_lock(task);
+ if (__ptrace_may_access(task, mode)) {
+ mm = ERR_PTR(-EACCES);
+ goto out;
+ }
+
+ mm = task->mm;
+ if (mm) {
+ if (task->flags & PF_KTHREAD)
+ mm = NULL;
+ else
+ atomic_inc(&mm->mm_users);
+ }
+
+out:
+ task_unlock(task);
+ mutex_unlock(&task->signal->cred_guard_mutex);
+
+ return mm;
+}
+EXPORT_SYMBOL_GPL(get_check_task_mm);
+
/* Please note the differences between mmput and mm_release.
* mmput is called whenever we stop holding onto a mm_struct,
* error success whatever.
diff --git a/mm/process_vm_access.c b/mm/process_vm_access.c
index e920aa3..aa8009d 100644
--- a/mm/process_vm_access.c
+++ b/mm/process_vm_access.c
@@ -298,23 +298,15 @@ static ssize_t process_vm_rw_core(pid_t pid, const struct iovec *lvec,
goto free_proc_pages;
}
- task_lock(task);
- if (__ptrace_may_access(task, PTRACE_MODE_ATTACH)) {
- task_unlock(task);
- rc = -EPERM;
- goto put_task_struct;
- }
- mm = task->mm;
-
- if (!mm || (task->flags & PF_KTHREAD)) {
- task_unlock(task);
- rc = -EINVAL;
+ mm = get_check_task_mm(task, PTRACE_MODE_ATTACH);
+ if (!mm || IS_ERR(mm)) {
+ if (!mm)
+ rc = -EINVAL;
+ else
+ rc = -EPERM;
goto put_task_struct;
}
- atomic_inc(&mm->mm_users);
- task_unlock(task);
-
for (i = 0; i < riovcnt && iov_l_curr_idx < liovcnt; i++) {
rc = process_vm_rw_single_vec(
(unsigned long)rvec[i].iov_base, rvec[i].iov_len,
--
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