diff options
| author | Michel Lespinasse <walken@google.com> | 2013-02-22 16:32:46 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2013-02-23 17:50:11 -0800 |
| commit | 1869305009857cdeaabe6283bcdc2359c5784543 (patch) | |
| tree | a8a500c71e7aa3a645322635f3d591c16601af27 /mm/mlock.c | |
| parent | cea10a19b7972a1954c4a2d05a7de8db48b444fb (diff) | |
| download | lwn-1869305009857cdeaabe6283bcdc2359c5784543.tar.gz lwn-1869305009857cdeaabe6283bcdc2359c5784543.zip | |
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 <walken@google.com>
Acked-by: Rik van Riel <riel@redhat.com>
Tested-by: Andy Lutomirski <luto@amacapital.net>
Cc: Greg Ungerer <gregungerer@westnet.com.au>
Cc: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/mlock.c')
| -rw-r--r-- | mm/mlock.c | 19 |
1 files changed, 10 insertions, 9 deletions
diff --git a/mm/mlock.c b/mm/mlock.c index 569400a5d079..d6378feb2950 100644 --- a/mm/mlock.c +++ b/mm/mlock.c @@ -340,9 +340,9 @@ static int do_mlock(unsigned long start, size_t len, int on) /* Here we know that vma->vm_start <= nstart < vma->vm_end. */ - newflags = vma->vm_flags | VM_LOCKED; - if (!on) - newflags &= ~VM_LOCKED; + newflags = vma->vm_flags & ~VM_LOCKED; + if (on) + newflags |= VM_LOCKED | VM_POPULATE; tmp = vma->vm_end; if (tmp > end) @@ -402,7 +402,8 @@ int __mm_populate(unsigned long start, unsigned long len, int ignore_errors) * range with the first VMA. Also, skip undesirable VMA types. */ nend = min(end, vma->vm_end); - if (vma->vm_flags & (VM_IO | VM_PFNMAP)) + if ((vma->vm_flags & (VM_IO | VM_PFNMAP | VM_POPULATE)) != + VM_POPULATE) continue; if (nstart < vma->vm_start) nstart = vma->vm_start; @@ -475,18 +476,18 @@ static int do_mlockall(int flags) struct vm_area_struct * vma, * prev = NULL; if (flags & MCL_FUTURE) - current->mm->def_flags |= VM_LOCKED; + current->mm->def_flags |= VM_LOCKED | VM_POPULATE; else - current->mm->def_flags &= ~VM_LOCKED; + current->mm->def_flags &= ~(VM_LOCKED | VM_POPULATE); if (flags == MCL_FUTURE) goto out; for (vma = current->mm->mmap; vma ; vma = prev->vm_next) { vm_flags_t newflags; - newflags = vma->vm_flags | VM_LOCKED; - if (!(flags & MCL_CURRENT)) - newflags &= ~VM_LOCKED; + newflags = vma->vm_flags & ~VM_LOCKED; + if (flags & MCL_CURRENT) + newflags |= VM_LOCKED | VM_POPULATE; /* Ignore errors */ mlock_fixup(vma, &prev, vma->vm_start, vma->vm_end, newflags); |