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| author | KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> | 2011-05-26 16:25:52 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2011-05-26 17:12:37 -0700 |
| commit | 30cd8903913dac7b0918807cac46be3ecde5a5a7 (patch) | |
| tree | 64022195d9a384c11b93a4b1299aa944b8293deb /fs/proc | |
| parent | a4dbf0ec2aa3e8aca6e63f598095750c232d50f1 (diff) | |
| download | lwn-30cd8903913dac7b0918807cac46be3ecde5a5a7.tar.gz lwn-30cd8903913dac7b0918807cac46be3ecde5a5a7.zip | |
proc: put check_mem_permission after __get_free_page in mem_write
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>
Diffstat (limited to 'fs/proc')
| -rw-r--r-- | fs/proc/base.c | 16 |
1 files changed, 9 insertions, 7 deletions
diff --git a/fs/proc/base.c b/fs/proc/base.c index 0c2c50cc2cca..4ede550517a6 100644 --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -894,20 +894,20 @@ static ssize_t mem_write(struct file * file, const char __user *buf, if (!task) goto out_no_task; + copied = -ENOMEM; + page = (char *)__get_free_page(GFP_TEMPORARY); + if (!page) + goto out_task; + mm = check_mem_permission(task); copied = PTR_ERR(mm); if (IS_ERR(mm)) - goto out_task; + goto out_free; copied = -EIO; if (file->private_data != (void *)((long)current->self_exec_id)) goto out_mm; - copied = -ENOMEM; - page = (char *)__get_free_page(GFP_TEMPORARY); - if (!page) - goto out_mm; - copied = 0; while (count > 0) { int this_len, retval; @@ -929,9 +929,11 @@ static ssize_t mem_write(struct file * file, const char __user *buf, count -= retval; } *ppos = dst; - free_page((unsigned long) page); + out_mm: mmput(mm); +out_free: + free_page((unsigned long) page); out_task: put_task_struct(task); out_no_task: |