commit: 9ab4233dd08036fe34a89c7dc6f47a8bf2eb29eb
From: Andy Lutomirski <[email protected]>
Date: Thu, 5 Jul 2012 16:00:11 -0700
Subject: 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 90ed52ebe481 ("[PATCH] holepunch: fix
mmap_sem i_mutex deadlock")
Cc: Hugh Dickins <[email protected]>
Cc: Miklos Szeredi <[email protected]>
Cc: Badari Pulavarty <[email protected]>
Cc: Nick Piggin <[email protected]>
Cc: [email protected]
Signed-off-by: Andy Lutomirski <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
---
mm/madvise.c | 18 ++++++++++++++----
1 files changed, 14 insertions(+), 4 deletions(-)
diff --git a/mm/madvise.c b/mm/madvise.c
index deff1b6..14d260f 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -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(¤t->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(¤t->mm->mmap_sem);
return error;
}
--
1.7.3.4
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