lkml.org 
[lkml]   [2002]   [Mar]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: [patch] mmap bug with drivers that adjust vm_start
On Tue, Mar 26, 2002 at 08:15:02PM +0100, Andrea Arcangeli wrote:
> > we could BUG() on getting a vma back from the new find_vma_prepare call.
>
> yes, it sounds a good idea to verify there's no other mapping in the way
> of the relocation (until a better fix is implemented), it's a slow path
> so we won't hurt performance.

Okay, updated patch for this is below. I also added a printk to give us
which mmap operation was invoked to aid in debugging.

> The good reason, is that currently we're literally corrupting the
> userspace with the senseless do_munmap call in the add<->addr+len area
> before the ->mmap lowlevel callback. And such an munmap is certainly not
> required to maintain source and binary compatibility (otherwise it would
> be insane in the first place :).

Ah, right. I disallow MAP_FIXED addresses that are not the "correct" offset,
so this case would fail, albeit with the do_munmap occurring. Personally,
I would rather see an mmap fail if it would collide with an existing mapping,
but that might break some applications.

Thanks for looking this over. Cheers,

-ben
--
"A man with a bass just walked in,
and he's putting it down
on the floor."

:r ~/patches/v2.4.19-pre4-mmap_fix-2.diff
--- retest.3/mm/mmap.c.org Mon Mar 25 19:38:10 2002
+++ retest.3/mm/mmap.c Tue Mar 26 15:01:47 2002
@@ -14,6 +14,7 @@
#include <linux/file.h>
#include <linux/fs.h>
#include <linux/personality.h>
+#include <linux/compiler.h>

#include <asm/uaccess.h>
#include <asm/pgalloc.h>
@@ -548,7 +549,19 @@
* Answer: Yes, several device drivers can do it in their
* f_op->mmap method. -DaveM
*/
- addr = vma->vm_start;
+ if (addr != vma->vm_start) {
+ /* Since addr changed, we rely on the mmap op to prevent
+ * collisions with existing vmas and just use find_vma_prepare
+ * to update the tree pointers.
+ */
+ addr = vma->vm_start;
+ if (unlikely(NULL != find_vma_prepare(mm, addr, &prev,
+ &rb_link, &rb_parent))) {
+ printk(KERN_ERR "buggy mmap operation: [<%p>]\n",
+ file ? file->f_op->mmap : NULL);
+ BUG();
+ }
+ }

vma_link(mm, vma, prev, rb_link, rb_parent);
if (correct_wcount)
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 13:25    [W:0.128 / U:0.156 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site