From 1869305009857cdeaabe6283bcdc2359c5784543 Mon Sep 17 00:00:00 2001 From: Michel Lespinasse Date: Fri, 22 Feb 2013 16:32:46 -0800 Subject: 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 --- mm/mmap.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-) (limited to 'mm/mmap.c') diff --git a/mm/mmap.c b/mm/mmap.c index 8826c77513a..39a3944e165 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -1306,9 +1306,7 @@ unsigned long do_mmap_pgoff(struct file *file, unsigned long addr, } addr = mmap_region(file, addr, len, vm_flags, pgoff); - if (!IS_ERR_VALUE(addr) && - ((vm_flags & VM_LOCKED) || - (flags & (MAP_POPULATE | MAP_NONBLOCK)) == MAP_POPULATE)) + if (!IS_ERR_VALUE(addr) && (vm_flags & VM_POPULATE)) *populate = true; return addr; } -- cgit v1.2.3-18-g5258