From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail137.messagelabs.com (mail137.messagelabs.com [216.82.249.19]) by kanga.kvack.org (Postfix) with SMTP id 832486B0082 for ; Thu, 14 Jan 2010 08:58:56 -0500 (EST) From: David Howells Subject: [PATCH 5/6] NOMMU: Fix race between ramfs truncation and shared mmap Date: Thu, 14 Jan 2010 13:58:51 +0000 Message-ID: <20100114135850.10482.6205.stgit@warthog.procyon.org.uk> In-Reply-To: <20100114135830.10482.54124.stgit@warthog.procyon.org.uk> References: <20100114135830.10482.54124.stgit@warthog.procyon.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: torvalds@osdl.org, akpm@linux-foundation.org Cc: viro@ZenIV.linux.org.uk, vapier@gentoo.org, lethal@linux-sh.org, dhowells@redhat.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org List-ID: 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 Acked-by: Al Viro --- 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 2efc571..2665313 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; } -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org