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proc: put check_mem_permission after __get_free_page in mem_write

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It whould be better if put check_mem_permission after __get_free_page in
mem_write, to be same as function mem_read.

Hugh Dickins explained the reason.

    check_mem_permission gets a reference to the mm.  If we __get_free_page
    after check_mem_permission, imagine what happens if the system is out
    of memory, and the mm we're looking at is selected for killing by the
    OOM killer: while we wait in __get_free_page for more memory, no memory
    is freed from the selected mm because it cannot reach exit_mmap while
    we hold that reference.

Reported-by: Jovi Zhang <bookjovi@gmail.com>
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Acked-by: Hugh Dickins <hughd@google.com>
Reviewed-by: Stephen Wilson <wilsons@start.ca>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
KOSAKI Motohiro 2011-05-26 16:25:52 -07:00 committed by Linus Torvalds
parent a4dbf0ec2a
commit 30cd890391
1 changed files with 12 additions and 10 deletions
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22
fs/proc/base.c
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@ -894,18 +894,18 @@ static ssize_t mem_write(struct file * file, const char __user *buf,
if (!task) if (!task)
goto out_no_task; goto out_no_task;
mm = check_mem_permission(task);
copied = PTR_ERR(mm);
if (IS_ERR(mm))
goto out_task;
copied = -EIO;
if (file->private_data != (void *)((long)current->self_exec_id))
goto out_mm;
copied = -ENOMEM; copied = -ENOMEM;
page = (char *)__get_free_page(GFP_TEMPORARY); page = (char *)__get_free_page(GFP_TEMPORARY);
if (!page) if (!page)
goto out_task;
mm = check_mem_permission(task);
copied = PTR_ERR(mm);
if (IS_ERR(mm))
goto out_free;
copied = -EIO;
if (file->private_data != (void *)((long)current->self_exec_id))
goto out_mm; goto out_mm;
copied = 0; copied = 0;
@ -929,9 +929,11 @@ static ssize_t mem_write(struct file * file, const char __user *buf,
count -= retval; count -= retval;
} }
*ppos = dst; *ppos = dst;
free_page((unsigned long) page);
out_mm: out_mm:
mmput(mm); mmput(mm);
out_free:
free_page((unsigned long) page);
out_task: out_task:
put_task_struct(task); put_task_struct(task);
out_no_task: out_no_task: