From 81759b5b221107488bda99fe7beeb7b734f61133 Mon Sep 17 00:00:00 2001 From: David Howells <dhowells@redhat.com> Date: Fri, 15 Jan 2010 17:01:36 -0800 Subject: 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> --- fs/ramfs/file-nommu.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) (limited to 'fs') diff --git a/fs/ramfs/file-nommu.c b/fs/ramfs/file-nommu.c index 2efc57173fd..266531343aa 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; } -- cgit v1.2.3-18-g5258