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Message-ID: <Pine.LNX.4.64.0703161055370.15253@sbz-30.cs.Helsinki.FI>
Date: Fri, 16 Mar 2007 10:56:02 +0200 (EET)
From: Pekka J Enberg <penberg@...helsinki.fi>
To: akpm@...ux-foundation.org
cc: nickpiggin@...oo.com.au, linux-kernel@...r.kernel.org
Subject: [PATCH] revoke: need ->mmap_sem to modify vma->vm_flags
From: Pekka Enberg <penberg@...helsinki.fi>
As pointed out by Nick Piggin, modifying vma->vm_flags without
->mmap_sem can corrupt the flags. This changes revoke_mapping() to
drop ->i_mmap_lock and rescanning vmas of the parent mm under
->mmap_sem.
Cc: Nick Piggin <nickpiggin@...oo.com.au>
Signed-off-by: Pekka Enberg <penberg@...helsinki.fi>
---
fs/revoke.c | 86 +++++++++++++++++++++++++++++++++++++++++-------------------
1 file changed, 60 insertions(+), 26 deletions(-)
Index: uml-2.6/fs/revoke.c
===================================================================
--- uml-2.6.orig/fs/revoke.c 2007-03-16 09:31:22.000000000 +0200
+++ uml-2.6/fs/revoke.c 2007-03-16 10:54:18.000000000 +0200
@@ -159,6 +159,22 @@ for (fd = 0; fd < fdt->max_fds; fd++) {
return err;
}
+static inline bool need_revoke(struct vm_area_struct *vma,
+ struct file *to_exclude)
+{
+ if (vma->vm_flags & VM_REVOKED)
+ return false;
+
+ if (!(vma->vm_flags & VM_SHARED))
+ return false;
+
+ return vma->vm_file != to_exclude;
+}
+
+/*
+ * LOCKING: down_write(&mm->mmap_sem)
+ * -> spin_lock(&mapping->i_mmap_lock)
+ */
static int revoke_vma(struct vm_area_struct *vma, struct zap_details *details)
{
unsigned long restart_addr, start_addr, end_addr;
@@ -167,13 +183,8 @@ static int revoke_vma(struct vm_area_str
start_addr = vma->vm_start;
end_addr = vma->vm_end;
- /*
- * Not holding ->mmap_sem here but we must watch out for page
- * faults and after the shared mappings have been taken down
- * and sys_mmap() trying to remap the revoked range.
- */
vma->vm_flags |= VM_REVOKED;
- smp_mb();
+
again:
restart_addr = zap_page_range(vma, start_addr, end_addr - start_addr,
details);
@@ -195,48 +206,71 @@ return 0;
return -EINTR;
}
+/*
+ * LOCKING: spin_lock(&mapping->i_mmap_lock)
+ */
+static void revoke_mm(struct mm_struct *mm, struct address_space *mapping,
+ struct file *to_exclude)
+{
+ struct vm_area_struct *vma;
+ struct zap_details details;
+
+ details.i_mmap_lock = &mapping->i_mmap_lock;
+
+ spin_unlock(&mapping->i_mmap_lock);
+ down_write(&mm->mmap_sem);
+ spin_lock(&mapping->i_mmap_lock);
+ restart:
+ for (vma = mm->mmap; vma != NULL; vma = vma->vm_next) {
+ if (!(vma->vm_flags & VM_SHARED) || vma->vm_file == to_exclude)
+ continue;
+
+ if (revoke_vma(vma, &details))
+ goto restart;
+ }
+ up_write(&mm->mmap_sem);
+}
+
+/*
+ * LOCKING: spin_lock(&mapping->i_mmap_lock)
+ */
static void revoke_mapping_tree(struct address_space *mapping,
- struct file *to_exclude,
- struct zap_details *details)
+ struct file *to_exclude)
{
struct vm_area_struct *vma;
struct prio_tree_iter iter;
- restart:
vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, 0, ULONG_MAX) {
- if ((vma->vm_flags & VM_SHARED) && vma->vm_file != to_exclude) {
- if (revoke_vma(vma, details))
- goto restart;
- }
+ if (likely(!need_revoke(vma, to_exclude)))
+ continue;
+
+ revoke_mm(vma->vm_mm, mapping, to_exclude);
}
}
+/*
+ * LOCKING: spin_lock(&mapping->i_mmap_lock)
+ */
static void revoke_mapping_list(struct address_space *mapping,
- struct file *to_exclude,
- struct zap_details *details)
+ struct file *to_exclude)
{
struct vm_area_struct *vma;
- restart:
list_for_each_entry(vma, &mapping->i_mmap_nonlinear, shared.vm_set.list) {
- if ((vma->vm_flags & VM_SHARED) && vma->vm_file != to_exclude) {
- if (revoke_vma(vma, details))
- goto restart;
- }
+ if (likely(!need_revoke(vma, to_exclude)))
+ continue;
+
+ revoke_mm(vma->vm_mm, mapping, to_exclude);
}
}
static void revoke_mapping(struct address_space *mapping, struct file *to_exclude)
{
- struct zap_details details;
-
- details.i_mmap_lock = &mapping->i_mmap_lock;
-
spin_lock(&mapping->i_mmap_lock);
if (unlikely(!prio_tree_empty(&mapping->i_mmap)))
- revoke_mapping_tree(mapping, to_exclude, &details);
+ revoke_mapping_tree(mapping, to_exclude);
if (unlikely(!list_empty(&mapping->i_mmap_nonlinear)))
- revoke_mapping_list(mapping, to_exclude, &details);
+ revoke_mapping_list(mapping, to_exclude);
spin_unlock(&mapping->i_mmap_lock);
}
-
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