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Date: Tue, 27 Mar 2007 10:14:58 +0300 (EEST)
From: Pekka J Enberg <penberg@...helsinki.fi>
To: akpm@...ux-foundation.org
cc: linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] revoke: break cow for private mappings
From: Pekka Enberg <penberg@...helsinki.fi>
We need to break COW for private mappings to make sure a process cannot
read new data after an inode has been revoked.
Signed-off-by: Pekka Enberg <penberg@...helsinki.fi>
---
fs/revoke.c | 85 +++++++++++++++++++++++++++++++++++++++++++++++++++---------
1 file changed, 73 insertions(+), 12 deletions(-)
Index: uml-2.6/fs/revoke.c
===================================================================
--- uml-2.6.orig/fs/revoke.c 2007-03-26 18:10:24.000000000 +0300
+++ uml-2.6/fs/revoke.c 2007-03-26 18:27:25.000000000 +0300
@@ -174,12 +174,58 @@ static inline bool need_revoke(struct vm
if (file->f_path.dentry->d_inode != inode)
return false;
- if (!(vma->vm_flags & VM_SHARED))
- return false;
-
return file != to_exclude;
}
+static int __revoke_break_cow(struct task_struct *tsk, struct inode *inode,
+ struct file *to_exclude)
+{
+ struct mm_struct *mm = tsk->mm;
+ struct vm_area_struct *vma;
+ int err = 0;
+
+ down_write(&mm->mmap_sem);
+ for (vma = mm->mmap; vma != NULL; vma = vma->vm_next) {
+ int ret;
+
+ if (vma->vm_flags & VM_SHARED)
+ continue;
+
+ if (!need_revoke(vma, inode, to_exclude))
+ continue;
+
+ ret = get_user_pages(tsk, tsk->mm, vma->vm_start,
+ vma->vm_end-vma->vm_start, 1, 1, NULL,
+ NULL);
+ if (ret < 0) {
+ err = ret;
+ break;
+ }
+ }
+ up_write(&mm->mmap_sem);
+ return err;
+}
+
+static int revoke_break_cow(struct revoke_table *table, struct inode *inode,
+ struct file *to_exclude)
+{
+ unsigned long i;
+ int err = 0;
+
+ for (i = 0; i < table->end; i++) {
+ struct revokefs_inode_info *info;
+ struct file *this;
+
+ this = table->files[i];
+ info = revokefs_i(this->f_dentry->d_inode);
+
+ err = __revoke_break_cow(info->owner, inode, to_exclude);
+ if (err)
+ break;
+ }
+ return err;
+}
+
/*
* LOCKING: down_write(&mm->mmap_sem)
* -> spin_lock(&mapping->i_mmap_lock)
@@ -235,6 +281,9 @@ int err = 0;
goto out;
}
for (vma = mm->mmap; vma != NULL; vma = vma->vm_next) {
+ if (!(vma->vm_flags & VM_SHARED))
+ continue;
+
if (!need_revoke(vma, mapping->host, to_exclude))
continue;
@@ -261,6 +310,9 @@ int try_again = 0;
vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, 0, ULONG_MAX) {
int err;
+ if (!(vma->vm_flags & VM_SHARED))
+ continue;
+
if (likely(!need_revoke(vma, mapping->host, to_exclude)))
continue;
@@ -380,12 +432,9 @@ for (i = 0; i < table->end; i++) {
put_task_struct(info->owner);
info->owner = NULL; /* To avoid restoring closed file. */
if (err)
- goto failed;
+ goto out;
}
- return 0;
-
- failed:
- restore_files(table);
+ out:
return err;
}
@@ -527,10 +576,8 @@ int err = 0;
exit_loop:
read_unlock(&tasklist_lock);
- if (err) {
- restore_files(table);
- goto out_free_table;
- }
+ if (err)
+ goto out_restore;
/*
* Take down shared memory mappings.
@@ -538,13 +585,27 @@ int err = 0;
revoke_mapping(inode->i_mapping, to_exclude);
/*
+ * Break COW for private mappings.
+ */
+ err = revoke_break_cow(table, inode, to_exclude);
+ if (err)
+ goto out_restore;
+
+ /*
* Now, revoke the files for good.
*/
err = revoke_files(table);
+ if (err)
+ goto out_restore;
+
out_free_table:
free_revoke_table(table);
out:
return err;
+
+ out_restore:
+ restore_files(table);
+ goto out_free_table;
}
asmlinkage long sys_revokeat(int dfd, const char __user * filename)
-
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