Patchwork [Lucid/Natty,CVE-2012-3511] mm: Hold a file reference in madvise_remove

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Submitter Tim Gardner
Date Aug. 30, 2012, 3:22 p.m.
Message ID <1346340168-13685-1-git-send-email-tim.gardner@canonical.com>
Download mbox | patch
Permalink /patch/180826/
State New
Headers show

Comments

Tim Gardner - Aug. 30, 2012, 3:22 p.m.
From: Andy Lutomirski <luto@amacapital.net>

CVE-2012-3511

BugLink: http://bugs.launchpad.net/bugs/1042447

Otherwise the code races with munmap (causing a use-after-free
of the vma) or with close (causing a use-after-free of the struct
file).

The bug was introduced by commit 90ed52ebe481 ("[PATCH] holepunch: fix
mmap_sem i_mutex deadlock")

Cc: Hugh Dickins <hugh@veritas.com>
Cc: Miklos Szeredi <mszeredi@suse.cz>
Cc: Badari Pulavarty <pbadari@us.ibm.com>
Cc: Nick Piggin <npiggin@suse.de>
Cc: stable@vger.kernel.org
Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
(back ported from commit 9ab4233dd08036fe34a89c7dc6f47a8bf2eb29eb)

Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
---
 mm/madvise.c |   16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)
Herton Ronaldo Krzesinski - Aug. 30, 2012, 7:37 p.m.
On Thu, Aug 30, 2012 at 09:22:48AM -0600, Tim Gardner wrote:
> @@ -211,9 +214,16 @@ static long madvise_remove(struct vm_area_struct *vma,
>  	endoff = (loff_t)(end - vma->vm_start - 1)
>  			+ ((loff_t)vma->vm_pgoff << PAGE_SHIFT);
>  
> -	/* vmtruncate_range needs to take i_mutex and i_alloc_sem */
> +	/*
> +	 * Filesystem's fallocate may need to take i_mutex.  We need to

Just a minor nit here: for older versions it's still vmtruncate_range,
so perhaps the comment could be kept as:

"vmtruncate_range needs to take i_mutex and i_alloc_sem. We need to..."

but it doesn't change the result, just noted this. In any case Ack on
the backport.

> +	 * explicitly grab a reference because the vma (and hence the
> +	 * vma's reference to the file) can go away as soon as we drop
> +	 * mmap_sem.
> +	 */
> +	get_file(f);
>  	up_read(&current->mm->mmap_sem);
>  	error = vmtruncate_range(mapping->host, offset, endoff);
> +	fput(f);
>  	down_read(&current->mm->mmap_sem);
>  	return error;
>  }
> -- 
> 1.7.9.5
Brad Figg - Sept. 3, 2012, 2:40 p.m.
On 08/30/2012 08:22 AM, Tim Gardner wrote:
> From: Andy Lutomirski <luto@amacapital.net>
> 
> CVE-2012-3511
> 
> BugLink: http://bugs.launchpad.net/bugs/1042447
> 
> Otherwise the code races with munmap (causing a use-after-free
> of the vma) or with close (causing a use-after-free of the struct
> file).
> 
> The bug was introduced by commit 90ed52ebe481 ("[PATCH] holepunch: fix
> mmap_sem i_mutex deadlock")
> 
> Cc: Hugh Dickins <hugh@veritas.com>
> Cc: Miklos Szeredi <mszeredi@suse.cz>
> Cc: Badari Pulavarty <pbadari@us.ibm.com>
> Cc: Nick Piggin <npiggin@suse.de>
> Cc: stable@vger.kernel.org
> Signed-off-by: Andy Lutomirski <luto@amacapital.net>
> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
> (back ported from commit 9ab4233dd08036fe34a89c7dc6f47a8bf2eb29eb)
> 
> Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
> ---
>  mm/madvise.c |   16 +++++++++++++---
>  1 file changed, 13 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/madvise.c b/mm/madvise.c
> index 35b1479..e51291d 100644
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -5,6 +5,7 @@
>   * Copyright (C) 2002  Christoph Hellwig
>   */
>  
> +#include <linux/file.h>
>  #include <linux/mman.h>
>  #include <linux/pagemap.h>
>  #include <linux/syscalls.h>
> @@ -190,14 +191,16 @@ static long madvise_remove(struct vm_area_struct *vma,
>  	struct address_space *mapping;
>  	loff_t offset, endoff;
>  	int error;
> +	struct file *f;
>  
>  	*prev = NULL;	/* tell sys_madvise we drop mmap_sem */
>  
>  	if (vma->vm_flags & (VM_LOCKED|VM_NONLINEAR|VM_HUGETLB))
>  		return -EINVAL;
>  
> -	if (!vma->vm_file || !vma->vm_file->f_mapping
> -		|| !vma->vm_file->f_mapping->host) {
> +	f = vma->vm_file;
> +
> +	if (!f || !f->f_mapping || !f->f_mapping->host) {
>  			return -EINVAL;
>  	}
>  
> @@ -211,9 +214,16 @@ static long madvise_remove(struct vm_area_struct *vma,
>  	endoff = (loff_t)(end - vma->vm_start - 1)
>  			+ ((loff_t)vma->vm_pgoff << PAGE_SHIFT);
>  
> -	/* vmtruncate_range needs to take i_mutex and i_alloc_sem */
> +	/*
> +	 * Filesystem's fallocate may need to take i_mutex.  We need to
> +	 * explicitly grab a reference because the vma (and hence the
> +	 * vma's reference to the file) can go away as soon as we drop
> +	 * mmap_sem.
> +	 */
> +	get_file(f);
>  	up_read(&current->mm->mmap_sem);
>  	error = vmtruncate_range(mapping->host, offset, endoff);
> +	fput(f);
>  	down_read(&current->mm->mmap_sem);
>  	return error;
>  }
>
Herton Ronaldo Krzesinski - Sept. 3, 2012, 3:29 p.m.
Applied, with the fix in the comment to maintain reference to old
function.

Patch

diff --git a/mm/madvise.c b/mm/madvise.c
index 35b1479..e51291d 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -5,6 +5,7 @@ 
  * Copyright (C) 2002  Christoph Hellwig
  */
 
+#include <linux/file.h>
 #include <linux/mman.h>
 #include <linux/pagemap.h>
 #include <linux/syscalls.h>
@@ -190,14 +191,16 @@  static long madvise_remove(struct vm_area_struct *vma,
 	struct address_space *mapping;
 	loff_t offset, endoff;
 	int error;
+	struct file *f;
 
 	*prev = NULL;	/* tell sys_madvise we drop mmap_sem */
 
 	if (vma->vm_flags & (VM_LOCKED|VM_NONLINEAR|VM_HUGETLB))
 		return -EINVAL;
 
-	if (!vma->vm_file || !vma->vm_file->f_mapping
-		|| !vma->vm_file->f_mapping->host) {
+	f = vma->vm_file;
+
+	if (!f || !f->f_mapping || !f->f_mapping->host) {
 			return -EINVAL;
 	}
 
@@ -211,9 +214,16 @@  static long madvise_remove(struct vm_area_struct *vma,
 	endoff = (loff_t)(end - vma->vm_start - 1)
 			+ ((loff_t)vma->vm_pgoff << PAGE_SHIFT);
 
-	/* vmtruncate_range needs to take i_mutex and i_alloc_sem */
+	/*
+	 * Filesystem's fallocate may need to take i_mutex.  We need to
+	 * explicitly grab a reference because the vma (and hence the
+	 * vma's reference to the file) can go away as soon as we drop
+	 * mmap_sem.
+	 */
+	get_file(f);
 	up_read(&current->mm->mmap_sem);
 	error = vmtruncate_range(mapping->host, offset, endoff);
+	fput(f);
 	down_read(&current->mm->mmap_sem);
 	return error;
 }