1 files changed, 46 insertions, 80 deletions

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 9cde9edf9c4..d4548dd49b0 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -198,26 +198,6 @@ 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;
-        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, mode)) {
-                mmput(mm);
-                mm = ERR_PTR(-EACCES);
-        }
-        mutex_unlock(&task->signal->cred_guard_mutex);
-
-        return mm;
-}
-
 struct mm_struct *mm_for_maps(struct task_struct *task)
 {
         return mm_access(task, PTRACE_MODE_READ);
@@ -711,6 +691,13 @@ static int mem_open(struct inode* inode, struct file* file)
         if (IS_ERR(mm))
                 return PTR_ERR(mm);
 
+        if (mm) {
+                /* ensure this mm_struct can't be freed */
+                atomic_inc(&mm->mm_count);
+                /* but do not pin its memory */
+                mmput(mm);
+        }
+
         /* OK to pass negative loff_t, we can catch out-of-range */
         file->f_mode |= FMODE_UNSIGNED_OFFSET;
         file->private_data = mm;
@@ -718,57 +705,13 @@ static int mem_open(struct inode* inode, struct file* file)
         return 0;
 }
 
-static ssize_t mem_read(struct file * file, char __user * buf,
-                        size_t count, loff_t *ppos)
+static ssize_t mem_rw(struct file *file, char __user *buf,
+                        size_t count, loff_t *ppos, int write)
 {
-        int ret;
-        char *page;
-        unsigned long src = *ppos;
         struct mm_struct *mm = file->private_data;
-
-        if (!mm)
-                return 0;
-
-        page = (char *)__get_free_page(GFP_TEMPORARY);
-        if (!page)
-                return -ENOMEM;
-
-        ret = 0;
- 
-        while (count > 0) {
-                int this_len, retval;
-
-                this_len = (count > PAGE_SIZE) ? PAGE_SIZE : count;
-                retval = access_remote_vm(mm, src, page, this_len, 0);
-                if (!retval) {
-                        if (!ret)
-                                ret = -EIO;
-                        break;
-                }
-
-                if (copy_to_user(buf, page, retval)) {
-                        ret = -EFAULT;
-                        break;
-                }
- 
-                ret += retval;
-                src += retval;
-                buf += retval;
-                count -= retval;
-        }
-        *ppos = src;
-
-        free_page((unsigned long) page);
-        return ret;
-}
-
-static ssize_t mem_write(struct file * file, const char __user *buf,
-                         size_t count, loff_t *ppos)
-{
-        int copied;
+        unsigned long addr = *ppos;
+        ssize_t copied;
         char *page;
-        unsigned long dst = *ppos;
-        struct mm_struct *mm = file->private_data;
 
         if (!mm)
                 return 0;
@@ -778,31 +721,54 @@ static ssize_t mem_write(struct file * file, const char __user *buf,
                 return -ENOMEM;
 
         copied = 0;
+        if (!atomic_inc_not_zero(&mm->mm_users))
+                goto free;
+
         while (count > 0) {
-                int this_len, retval;
+                int this_len = min_t(int, count, PAGE_SIZE);
 
-                this_len = (count > PAGE_SIZE) ? PAGE_SIZE : count;
-                if (copy_from_user(page, buf, this_len)) {
+                if (write && copy_from_user(page, buf, this_len)) {
                         copied = -EFAULT;
                         break;
                 }
-                retval = access_remote_vm(mm, dst, page, this_len, 1);
-                if (!retval) {
+
+                this_len = access_remote_vm(mm, addr, page, this_len, write);
+                if (!this_len) {
                         if (!copied)
                                 copied = -EIO;
                         break;
                 }
-                copied += retval;
-                buf += retval;
-                dst += retval;
-                count -= retval;                        
+
+                if (!write && copy_to_user(buf, page, this_len)) {
+                        copied = -EFAULT;
+                        break;
+                }
+
+                buf += this_len;
+                addr += this_len;
+                copied += this_len;
+                count -= this_len;
         }
-        *ppos = dst;
+        *ppos = addr;
 
+        mmput(mm);
+free:
         free_page((unsigned long) page);
         return copied;
 }
 
+static ssize_t mem_read(struct file *file, char __user *buf,
+                        size_t count, loff_t *ppos)
+{
+        return mem_rw(file, buf, count, ppos, 0);
+}
+
+static ssize_t mem_write(struct file *file, const char __user *buf,
+                         size_t count, loff_t *ppos)
+{
+        return mem_rw(file, (char __user*)buf, count, ppos, 1);
+}
+
 loff_t mem_lseek(struct file *file, loff_t offset, int orig)
 {
         switch (orig) {
@@ -822,8 +788,8 @@ loff_t mem_lseek(struct file *file, loff_t offset, int orig)
 static int mem_release(struct inode *inode, struct file *file)
 {
         struct mm_struct *mm = file->private_data;
-
-        mmput(mm);
+        if (mm)
+                mmdrop(mm);
         return 0;
 }