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Date: Sat, 5 Jul 2008 01:02:01 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: "Alexey Dobriyan" <adobriyan@...il.com>
Cc: torvalds@...uxfoundation.org, mpm@...enic.com,
linux-kernel@...r.kernel.org
Subject: Re: *sigh* /proc/*/pagemap
On Sat, 5 Jul 2008 11:44:54 +0400 "Alexey Dobriyan" <adobriyan@...il.com> wrote:
> On 7/5/08, Andrew Morton <akpm@...ux-foundation.org> wrote:
> > On Sat, 5 Jul 2008 05:07:02 +0400 "Alexey Dobriyan" <adobriyan@...il.com>
> > wrote:
>
> >> 3) unstatic struct pagemap_walk, so two threads won't fsckup each other
> >> (including those started by root, including flipping ->mm when you
> >> don't have permissions),
> >
> > Below
>
> Below.
>
> >> 4) remove second ptrace_may_attach(), and
> >
> > Can't find what you're referring to here.
>
> pagemap_read() contains two calls to ptrace_may_attach(),
> second one looks unneeded.
Agree.
> >> 5) check with microscope allocation there -- page-aligned address and size
> >> == 0
> >> should allocate 0 bytes, and
> >
> > Where?
>
> kmalloc() in pagemap_read(). kmalloc(0) and integer wraparound look possible.
hm, maybe. Plug that anyway. Used kcalloc() even though the memset
isn't needed (we need a non-zeroing kcalloc)
> >> 6) actually check that it works.
> >
> > Will have a shot.
>
> Ha-ha!
>
> > - unstatic struct pagemap_walk, so two threads won't fsckup each other
> > (including those started by root, including flipping ->mm when you don't
> > have permissions)
>
> > --- a/fs/proc/task_mmu.c~pagemap-fixes-to-pagemap_read
> > +++ a/fs/proc/task_mmu.c
> > @@ -641,6 +636,7 @@ static ssize_t pagemap_read(struct file
> > struct pagemapread pm;
> > int pagecount;
> > int ret = -ESRCH;
> > + static struct mm_walk pagemap_walk;
>
> No, can't have static here, two threads doing pagemap_read() will overwrite
> each other's .mm and "out" at least. Like "pm" it shouldn't be global.
doh, copy-n-paste strikes again.
From: Andrew Morton <akpm@...ux-foundation.org>
Fix some issues noted by Alexey:
- initialize pagemap_walk.mm to "mm" , so the code starts working as
advertised
- initialize ->private to "&pm" so it wouldn't immediately oops in
pagemap_pte_hole()
- unstatic struct pagemap_walk, so two threads won't fsckup each other
(including those started by root, including flipping ->mm when you don't
have permissions)
- pagemap_read() contains two calls to ptrace_may_attach(), second one
looks unneeded.
- avoid possible kmalloc(0) and integer wraparound.
Cc: Alexey Dobriyan <adobriyan@...il.com>
Cc: Matt Mackall <mpm@...enic.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
---
fs/proc/task_mmu.c | 72 ++++++++++++++++++++++---------------------
1 file changed, 38 insertions(+), 34 deletions(-)
diff -puN fs/proc/task_mmu.c~pagemap-fixes-to-pagemap_read fs/proc/task_mmu.c
--- a/fs/proc/task_mmu.c~pagemap-fixes-to-pagemap_read
+++ a/fs/proc/task_mmu.c
@@ -602,11 +602,6 @@ static int pagemap_pte_range(pmd_t *pmd,
return err;
}
-static struct mm_walk pagemap_walk = {
- .pmd_entry = pagemap_pte_range,
- .pte_hole = pagemap_pte_hole
-};
-
/*
* /proc/pid/pagemap - an array mapping virtual pages to pfns
*
@@ -641,6 +636,11 @@ static ssize_t pagemap_read(struct file
struct pagemapread pm;
int pagecount;
int ret = -ESRCH;
+ struct mm_walk pagemap_walk;
+ unsigned long src;
+ unsigned long svpfn;
+ unsigned long start_vaddr;
+ unsigned long end_vaddr;
if (!task)
goto out;
@@ -659,11 +659,15 @@ static ssize_t pagemap_read(struct file
if (!mm)
goto out_task;
- ret = -ENOMEM;
+
uaddr = (unsigned long)buf & PAGE_MASK;
uend = (unsigned long)(buf + count);
pagecount = (PAGE_ALIGN(uend) - uaddr) / PAGE_SIZE;
- pages = kmalloc(pagecount * sizeof(struct page *), GFP_KERNEL);
+ ret = 0;
+ if (pagecount == 0)
+ goto out_mm;
+ pages = kcalloc(pagecount, sizeof(struct page *), GFP_KERNEL);
+ ret = -ENOMEM;
if (!pages)
goto out_mm;
@@ -684,33 +688,33 @@ static ssize_t pagemap_read(struct file
pm.out = (u64 *)buf;
pm.end = (u64 *)(buf + count);
- if (!ptrace_may_attach(task)) {
- ret = -EIO;
- } else {
- unsigned long src = *ppos;
- unsigned long svpfn = src / PM_ENTRY_BYTES;
- unsigned long start_vaddr = svpfn << PAGE_SHIFT;
- unsigned long end_vaddr = TASK_SIZE_OF(task);
-
- /* watch out for wraparound */
- if (svpfn > TASK_SIZE_OF(task) >> PAGE_SHIFT)
- start_vaddr = end_vaddr;
-
- /*
- * The odds are that this will stop walking way
- * before end_vaddr, because the length of the
- * user buffer is tracked in "pm", and the walk
- * will stop when we hit the end of the buffer.
- */
- ret = walk_page_range(start_vaddr, end_vaddr,
- &pagemap_walk);
- if (ret == PM_END_OF_BUFFER)
- ret = 0;
- /* don't need mmap_sem for these, but this looks cleaner */
- *ppos += (char *)pm.out - buf;
- if (!ret)
- ret = (char *)pm.out - buf;
- }
+ pagemap_walk.pmd_entry = pagemap_pte_range;
+ pagemap_walk.pte_hole = pagemap_pte_hole;
+ pagemap_walk.mm = mm;
+ pagemap_walk.private = ±
+
+ src = *ppos;
+ svpfn = src / PM_ENTRY_BYTES;
+ start_vaddr = svpfn << PAGE_SHIFT;
+ end_vaddr = TASK_SIZE_OF(task);
+
+ /* watch out for wraparound */
+ if (svpfn > TASK_SIZE_OF(task) >> PAGE_SHIFT)
+ start_vaddr = end_vaddr;
+
+ /*
+ * The odds are that this will stop walking way
+ * before end_vaddr, because the length of the
+ * user buffer is tracked in "pm", and the walk
+ * will stop when we hit the end of the buffer.
+ */
+ ret = walk_page_range(start_vaddr, end_vaddr, &pagemap_walk);
+ if (ret == PM_END_OF_BUFFER)
+ ret = 0;
+ /* don't need mmap_sem for these, but this looks cleaner */
+ *ppos += (char *)pm.out - buf;
+ if (!ret)
+ ret = (char *)pm.out - buf;
out_pages:
for (; pagecount; pagecount--) {
_
--
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