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 | |
parent | cea10a19b7972a1954c4a2d05a7de8db48b444fb (diff) | |
download | kernel_goldelico_gta04-1869305009857cdeaabe6283bcdc2359c5784543.zip kernel_goldelico_gta04-1869305009857cdeaabe6283bcdc2359c5784543.tar.gz kernel_goldelico_gta04-1869305009857cdeaabe6283bcdc2359c5784543.tar.bz2 |
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>
-rw-r--r-- | include/linux/mm.h | 1 | ||||
-rw-r--r-- | include/linux/mman.h | 4 | ||||
-rw-r--r-- | mm/fremap.c | 12 | ||||
-rw-r--r-- | mm/mlock.c | 19 | ||||
-rw-r--r-- | mm/mmap.c | 4 |
5 files changed, 25 insertions, 15 deletions
diff --git a/include/linux/mm.h b/include/linux/mm.h index 0c34d34..9a5fcde 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 9aa863d..61c7a87 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 */ 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); 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 @@ -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); @@ -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; } |