[PATCH] NOMMU: Don't pass NULL pointers to fput() in do_mmap_pgoff()

[PATCH] NOMMU: Don't pass NULL pointers to fput() in do_mmap_pgoff()

[David Howells]

Don't pass NULL pointers to fput() in the error handling paths of the NOMMU
do_mmap_pgoff() as it can't handle it.

The following can be used as a test program:

	int main() { static long long a[1024 * 1024 * 20] = { 0 }; return a;}

Without the patch, the code oopses in atomic_long_dec_and_test() as called by
fput() after the kernel complains that it can't allocate that big a chunk of
memory.  With the patch, the kernel just complains about the allocation size
and then the program segfaults during execve() as execve() can't complete the
allocation of all the new ELF program segments.

Reported-by: Robin Getz <rgetz@blackfin.uclinux.org>
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Robin Getz <rgetz@blackfin.uclinux.org>
---

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


diff --git a/mm/nommu.c b/mm/nommu.c
index cfea46c..969392c 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -1364,9 +1364,11 @@ share:
 error_just_free:
 	up_write(&nommu_region_sem);
 error:
-	fput(region->vm_file);
+	if (region->vm_file)
+		fput(region->vm_file);
 	kmem_cache_free(vm_region_jar, region);
-	fput(vma->vm_file);
+	if (vma->vm_file)
+		fput(vma->vm_file);
 	if (vma->vm_flags & VM_EXECUTABLE)
 		removed_exe_file_vma(vma->vm_mm);
 	kmem_cache_free(vm_area_cachep, vma);

Re: [PATCH] NOMMU: Don't pass NULL pointers to fput() in do_mmap_pgoff()

[Andrew Morton]

On Fri, 30 Oct 2009 13:13:26 +0000
David Howells <dhowells@redhat.com> wrote:

> Don't pass NULL pointers to fput() in the error handling paths of the NOMMU
> do_mmap_pgoff() as it can't handle it.
> 
> The following can be used as a test program:
> 
> 	int main() { static long long a[1024 * 1024 * 20] = { 0 }; return a;}
> 
> Without the patch, the code oopses in atomic_long_dec_and_test() as called by
> fput() after the kernel complains that it can't allocate that big a chunk of
> memory.  With the patch, the kernel just complains about the allocation size
> and then the program segfaults during execve() as execve() can't complete the
> allocation of all the new ELF program segments.
> 
> Reported-by: Robin Getz <rgetz@blackfin.uclinux.org>
> Signed-off-by: David Howells <dhowells@redhat.com>
> Acked-by: Robin Getz <rgetz@blackfin.uclinux.org>
> ---
> 
>  mm/nommu.c |    6 ++++--
>  1 files changed, 4 insertions(+), 2 deletions(-)
> 
> 
> diff --git a/mm/nommu.c b/mm/nommu.c
> index cfea46c..969392c 100644
> --- a/mm/nommu.c
> +++ b/mm/nommu.c
> @@ -1364,9 +1364,11 @@ share:
>  error_just_free:
>  	up_write(&nommu_region_sem);
>  error:
> -	fput(region->vm_file);
> +	if (region->vm_file)
> +		fput(region->vm_file);
>  	kmem_cache_free(vm_region_jar, region);
> -	fput(vma->vm_file);
> +	if (vma->vm_file)
> +		fput(vma->vm_file);
>  	if (vma->vm_flags & VM_EXECUTABLE)
>  		removed_exe_file_vma(vma->vm_mm);
>  	kmem_cache_free(vm_area_cachep, vma);

Seems like a pretty obvious -stable candidate, but no stable tag in the
changelog?

Assuming this is needed in -stable, do we know how far back in time the
bug exists?