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| author | David Howells <dhowells@redhat.com> | 2010-01-15 17:01:36 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2010-01-16 12:15:40 -0800 |
| commit | 81759b5b221107488bda99fe7beeb7b734f61133 (patch) | |
| tree | 2ca1207d4ae5d6bbdc49db727a35b22a502fc76f /fs | |
| parent | efc1a3b16930c41d64ffefde16b87d82f603a8a0 (diff) | |
| download | linux-81759b5b221107488bda99fe7beeb7b734f61133.tar.bz2 | |
nommu: fix race between ramfs truncation and shared mmap
Fix the race between the truncation of a ramfs file and an attempt to make
a shared mmap of region of that file.
The problem is that do_mmap_pgoff() calls f_op->get_unmapped_area() to
verify that the file region is made of contiguous pages and to find its
base address - but there isn't any locking to guarantee this region until
vma_prio_tree_insert() is called by add_vma_to_mm().
Note that moving the functionality into f_op->mmap() doesn't help as that
is also called before vma_prio_tree_insert().
Instead make ramfs_nommu_check_mappings() grab nommu_region_sem whilst it
does its checks. This means that this function will wait whilst mmaps
take place.
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Al Viro <viro@zeniv.linux.org.uk>
Cc: Greg Ungerer <gerg@snapgear.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'fs')
| -rw-r--r-- | fs/ramfs/file-nommu.c | 7 |
1 files changed, 6 insertions, 1 deletions
diff --git a/fs/ramfs/file-nommu.c b/fs/ramfs/file-nommu.c index 2efc57173fd7..266531343aae 100644 --- a/fs/ramfs/file-nommu.c +++ b/fs/ramfs/file-nommu.c @@ -131,6 +131,8 @@ static int ramfs_nommu_check_mappings(struct inode *inode, struct vm_area_struct *vma; struct prio_tree_iter iter; + down_write(&nommu_region_sem); + /* search for VMAs that fall within the dead zone */ vma_prio_tree_foreach(vma, &iter, &inode->i_mapping->i_mmap, newsize >> PAGE_SHIFT, @@ -138,10 +140,13 @@ static int ramfs_nommu_check_mappings(struct inode *inode, ) { /* found one - only interested if it's shared out of the page * cache */ - if (vma->vm_flags & VM_SHARED) + if (vma->vm_flags & VM_SHARED) { + up_write(&nommu_region_sem); return -ETXTBSY; /* not quite true, but near enough */ + } } + up_write(&nommu_region_sem); return 0; } |