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SubjectRe: [PATCH 4/9] mm: use mm_populate() for blocking remap_file_pages()
On Sun, 10 Mar 2013 20:55:21 +0200 Tommi Rantala <tt.rantala@gmail.com> wrote:

> 2012/12/21 Michel Lespinasse <walken@google.com>:
> > Signed-off-by: Michel Lespinasse <walken@google.com>
>
> Hello, this patch introduced the following bug, seen while fuzzing with trinity:
>
> [ 396.825414] BUG: unable to handle kernel NULL pointer dereference
> at 0000000000000050
>
> ...
>
> > + vm_flags = vma->vm_flags;
>
> When find_vma() fails, vma is NULL here.

Yup, thanks.

This, methinks:


From: Andrew Morton <akpm@linux-foundation.org>
Subject: mm/fremap.c: fix oops on error path

If find_vma() fails, sys_remap_file_pages() will dereference `vma', which
contains NULL. Fix it by checking the pointer.

(We could alternatively check for err==0, but this seems more direct)

(The vm_flags change is to squish a bogus used-uninitialised warning
without adding extra code).

Reported-by: Tommi Rantala <tt.rantala@gmail.com>
Cc: Michel Lespinasse <walken@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

mm/fremap.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff -puN mm/fremap.c~mm-fremapc-fix-oops-on-error-path mm/fremap.c
--- a/mm/fremap.c~mm-fremapc-fix-oops-on-error-path
+++ a/mm/fremap.c
@@ -163,7 +163,8 @@ SYSCALL_DEFINE5(remap_file_pages, unsign
* and that the remapped range is valid and fully within
* the single existing vma.
*/
- if (!vma || !(vma->vm_flags & VM_SHARED))
+ vm_flags = vma->vm_flags;
+ if (!vma || !(vm_flags & VM_SHARED))
goto out;

if (!vma->vm_ops || !vma->vm_ops->remap_pages)
@@ -254,7 +255,8 @@ get_write_lock:
*/

out:
- vm_flags = vma->vm_flags;
+ if (vma)
+ vm_flags = vma->vm_flags;
if (likely(!has_write_lock))
up_read(&mm->mmap_sem);
else
_


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