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mm: Hold a file reference in madvise_remove

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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 90ed52ebe4 ("[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>
This commit is contained in:
Andy Lutomirski 2012-07-05 16:00:11 -07:00 committed by Linus Torvalds
parent 1b7fa4c271
commit 9ab4233dd0
1 changed files with 14 additions and 4 deletions
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18
mm/madvise.c
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@ -15,6 +15,7 @@
#include <linux/sched.h>
#include <linux/ksm.h>
#include <linux/fs.h>
#include <linux/file.h>
/*
* Any behaviour which results in changes to the vma->vm_flags needs to
@ -204,14 +205,16 @@ static long madvise_remove(struct vm_area_struct *vma,
{
loff_t offset;
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;
}
@ -221,11 +224,18 @@ static long madvise_remove(struct vm_area_struct *vma,
offset = (loff_t)(start - vma->vm_start)
+ ((loff_t)vma->vm_pgoff << PAGE_SHIFT);
/* filesystem's fallocate may need to take i_mutex */
/*
* 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 = do_fallocate(vma->vm_file,
error = do_fallocate(f,
FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
offset, end - start);
fput(f);
down_read(&current->mm->mmap_sem);
return error;
}