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authorMichel Lespinasse <walken@google.com>2013-02-22 16:32:46 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2013-02-23 17:50:11 -0800
commit1869305009857cdeaabe6283bcdc2359c5784543 (patch)
treea8a500c71e7aa3a645322635f3d591c16601af27 /include
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 <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 'include')
-rw-r--r--include/linux/mm.h1
-rw-r--r--include/linux/mman.h4
2 files changed, 4 insertions, 1 deletions
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 0c34d348681..9a5fcdeaa3a 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -87,6 +87,7 @@ extern unsigned int kobjsize(const void *objp);
#define VM_PFNMAP 0x00000400 /* Page-ranges managed without "struct page", just pure PFN */
#define VM_DENYWRITE 0x00000800 /* ETXTBSY on write attempts.. */
+#define VM_POPULATE 0x00001000
#define VM_LOCKED 0x00002000
#define VM_IO 0x00004000 /* Memory mapped I/O or similar */
diff --git a/include/linux/mman.h b/include/linux/mman.h
index 9aa863da287..61c7a87e5d2 100644
--- a/include/linux/mman.h
+++ b/include/linux/mman.h
@@ -79,6 +79,8 @@ calc_vm_flag_bits(unsigned long flags)
{
return _calc_vm_trans(flags, MAP_GROWSDOWN, VM_GROWSDOWN ) |
_calc_vm_trans(flags, MAP_DENYWRITE, VM_DENYWRITE ) |
- _calc_vm_trans(flags, MAP_LOCKED, VM_LOCKED );
+ ((flags & MAP_LOCKED) ? (VM_LOCKED | VM_POPULATE) : 0) |
+ (((flags & (MAP_POPULATE | MAP_NONBLOCK)) == MAP_POPULATE) ?
+ VM_POPULATE : 0);
}
#endif /* _LINUX_MMAN_H */