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Subject[PATCH RESEND] 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/).

This has been updated since I last sent it since the creation
of mm_access did almost exactly the same thing as parts of the
previous version of this patch did.

Regards,

Chris
--
cyeoh@au.ibm.com
Signed-off-by: Chris Yeoh <yeohc@au1.ibm.com>
Cc: stable@vger.kernel.org
fs/proc/base.c | 2 +-
include/linux/sched.h | 3 +++
mm/process_vm_access.c | 20 ++++++--------------
3 files changed, 10 insertions(+), 15 deletions(-)
diff --git a/fs/proc/base.c b/fs/proc/base.c
index 9cde9edf..0635dc0 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -198,7 +198,7 @@ static int proc_root_link(struct dentry *dentry, struct path *path)
return result;
}

-static struct mm_struct *mm_access(struct task_struct *task, unsigned int mode)
+struct mm_struct *mm_access(struct task_struct *task, unsigned int mode)
{
struct mm_struct *mm;
int err;
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 4032ec1..e6268d1 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2259,6 +2259,9 @@ 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 */
+struct mm_struct *mm_access(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/mm/process_vm_access.c b/mm/process_vm_access.c
index e920aa3..82b6824 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 = mm_access(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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