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Commit 9ab4233d authored by Andy Lutomirski's avatar Andy Lutomirski Committed by Linus Torvalds
Browse files

mm: Hold a file reference in madvise_remove 



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 90ed52eb ("[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: default avatarAndy Lutomirski <luto@amacapital.net>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 1b7fa4c2

mm/madvise.c

+14 −4
Original line number Original line Diff line number Diff line
@@ -15,6 +15,7 @@ 
#include <linux/sched.h>

#include <linux/sched.h>

#include <linux/ksm.h>

#include <linux/ksm.h>

#include <linux/fs.h>

#include <linux/fs.h>

#include <linux/file.h>





/*

/*

 * Any behaviour which results in changes to the vma->vm_flags needs to

 * 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;

	loff_t offset;

	int error;

	int error;

	struct file *f;





	*prev = NULL;	/* tell sys_madvise we drop mmap_sem */

	*prev = NULL;	/* tell sys_madvise we drop mmap_sem */





	if (vma->vm_flags & (VM_LOCKED|VM_NONLINEAR|VM_HUGETLB))

	if (vma->vm_flags & (VM_LOCKED|VM_NONLINEAR|VM_HUGETLB))

		return -EINVAL;

		return -EINVAL;





	if (!vma->vm_file || !vma->vm_file->f_mapping

	f = vma->vm_file;

		|| !vma->vm_file->f_mapping->host) {



	if (!f || !f->f_mapping || !f->f_mapping->host) {

			return -EINVAL;

			return -EINVAL;

	}

	}
@@ -221,11 +224,18 @@ static long madvise_remove(struct vm_area_struct *vma, 
	offset = (loff_t)(start - vma->vm_start)

	offset = (loff_t)(start - vma->vm_start)

			+ ((loff_t)vma->vm_pgoff << PAGE_SHIFT);

			+ ((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);

	up_read(&current->mm->mmap_sem);

	error = do_fallocate(vma->vm_file,

	error = do_fallocate(f,

				FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,

				FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,

				offset, end - start);

				offset, end - start);

	fput(f);

	down_read(&current->mm->mmap_sem);

	down_read(&current->mm->mmap_sem);

	return error;

	return error;

}

}