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Date: Thu, 20 Dec 2012 16:49:57 -0800
From: Michel Lespinasse <walken@...gle.com>
To: Andy Lutomirski <luto@...capital.net>,
Ingo Molnar <mingo@...nel.org>,
Al Viro <viro@...iv.linux.org.uk>,
Hugh Dickins <hughd@...gle.com>, Jorn_Engel <joern@...fs.org>,
Rik van Riel <riel@...hat.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: [PATCH 9/9] 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@...gle.com>
---
include/linux/mm.h | 1 +
include/linux/mman.h | 4 +++-
mm/fremap.c | 12 ++++++++++--
mm/mlock.c | 19 ++++++++++---------
mm/mmap.c | 4 +---
5 files changed, 25 insertions(+), 15 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index d32ace5fba93..77311274f0b5 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 d09dde1e57fb..e4ad758962e5 100644
--- a/include/linux/mman.h
+++ b/include/linux/mman.h
@@ -77,6 +77,8 @@ 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 */
diff --git a/mm/fremap.c b/mm/fremap.c
index 503a72387087..0cd4c11488ed 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);
fput(file);
if (IS_ERR_VALUE(addr)) {
err = addr;
@@ -224,6 +226,12 @@ get_write_lock:
mutex_unlock(&mapping->i_mmap_mutex);
}
+ 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
diff --git a/mm/mlock.c b/mm/mlock.c
index ab0cfe21f538..b1647fbd6bce 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;
@@ -475,9 +476,9 @@ static int do_mlockall(int flags)
struct vm_area_struct * vma, * prev = NULL;
unsigned int def_flags;
- def_flags = current->mm->def_flags & ~VM_LOCKED;
+ def_flags = current->mm->def_flags & ~(VM_LOCKED | VM_POPULATE);
if (flags & MCL_FUTURE)
- def_flags |= VM_LOCKED;
+ def_flags |= (VM_LOCKED | VM_POPULATE);
current->mm->def_flags = def_flags;
if (flags == MCL_FUTURE)
goto out;
@@ -485,9 +486,9 @@ static int do_mlockall(int flags)
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);
diff --git a/mm/mmap.c b/mm/mmap.c
index 290d023632e6..27f98850fa8c 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1153,9 +1153,7 @@ 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;
}
--
1.7.7.3
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