path: root/mm/fremap.c
diff options
authorMichel Lespinasse <>2013-02-23 00:32:46 (GMT)
committerLinus Torvalds <>2013-02-24 01:50:11 (GMT)
commit1869305009857cdeaabe6283bcdc2359c5784543 (patch)
treea8a500c71e7aa3a645322635f3d591c16601af27 /mm/fremap.c
parentcea10a19b7972a1954c4a2d05a7de8db48b444fb (diff)
mm: introduce VM_POPULATE flag to better deal with racy userspace programs
The vm_populate() code populates user mappings without constantly holding the mmap_sem. This makes it susceptible to racy userspace programs: the user mappings may change while vm_populate() is running, and in this case vm_populate() may end up populating the new mapping instead of the old one. In order to reduce the possibility of userspace getting surprised by this behavior, this change introduces the VM_POPULATE vma flag which gets set on vmas we want vm_populate() to work on. This way vm_populate() may still end up populating the new mapping after such a race, but only if the new mapping is also one that the user has requested (using MAP_SHARED, MAP_LOCKED or mlock) to be populated. Signed-off-by: Michel Lespinasse <> Acked-by: Rik van Riel <> Tested-by: Andy Lutomirski <> Cc: Greg Ungerer <> Cc: David Howells <> Signed-off-by: Andrew Morton <> Signed-off-by: Linus Torvalds <>
Diffstat (limited to 'mm/fremap.c')
1 files changed, 10 insertions, 2 deletions
diff --git a/mm/fremap.c b/mm/fremap.c
index 503a723..0cd4c11 100644
--- a/mm/fremap.c
+++ b/mm/fremap.c
@@ -204,8 +204,10 @@ get_write_lock:
unsigned long addr;
struct file *file = get_file(vma->vm_file);
- addr = mmap_region(file, start, size,
- vma->vm_flags, pgoff);
+ vm_flags = vma->vm_flags;
+ if (!(flags & MAP_NONBLOCK))
+ vm_flags |= VM_POPULATE;
+ addr = mmap_region(file, start, size, vm_flags, pgoff);
if (IS_ERR_VALUE(addr)) {
err = addr;
@@ -224,6 +226,12 @@ get_write_lock:
+ if (!(flags & MAP_NONBLOCK) && !(vma->vm_flags & VM_POPULATE)) {
+ if (!has_write_lock)
+ goto get_write_lock;
+ vma->vm_flags |= VM_POPULATE;
+ }
if (vma->vm_flags & VM_LOCKED) {
* drop PG_Mlocked flag for over-mapped range