From patchwork Thu Aug 30 15:22:48 2012 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Subject: [Lucid/Natty, CVE-2012-3511] mm: Hold a file reference in madvise_remove From: Tim Gardner X-Patchwork-Id: 180826 Message-Id: <1346340168-13685-1-git-send-email-tim.gardner@canonical.com> To: kernel-team@lists.ubuntu.com Date: Thu, 30 Aug 2012 09:22:48 -0600 From: Andy Lutomirski CVE-2012-3511 BugLink: http://bugs.launchpad.net/bugs/1042447 Otherwise the code races with munmap (causing a use-after-free of the vma) or with close (causing a use-after-free of the struct file). The bug was introduced by commit 90ed52ebe481 ("[PATCH] holepunch: fix mmap_sem i_mutex deadlock") Cc: Hugh Dickins Cc: Miklos Szeredi Cc: Badari Pulavarty Cc: Nick Piggin Cc: stable@vger.kernel.org Signed-off-by: Andy Lutomirski Signed-off-by: Linus Torvalds (back ported from commit 9ab4233dd08036fe34a89c7dc6f47a8bf2eb29eb) Signed-off-by: Tim Gardner --- mm/madvise.c | 16 +++++++++++++--- 1 file changed, 13 insertions(+), 3 deletions(-) diff --git a/mm/madvise.c b/mm/madvise.c index 35b1479..e51291d 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -5,6 +5,7 @@ * Copyright (C) 2002 Christoph Hellwig */ +#include #include #include #include @@ -190,14 +191,16 @@ static long madvise_remove(struct vm_area_struct *vma, struct address_space *mapping; loff_t offset, endoff; int error; + struct file *f; *prev = NULL; /* tell sys_madvise we drop mmap_sem */ if (vma->vm_flags & (VM_LOCKED|VM_NONLINEAR|VM_HUGETLB)) return -EINVAL; - if (!vma->vm_file || !vma->vm_file->f_mapping - || !vma->vm_file->f_mapping->host) { + f = vma->vm_file; + + if (!f || !f->f_mapping || !f->f_mapping->host) { return -EINVAL; } @@ -211,9 +214,16 @@ static long madvise_remove(struct vm_area_struct *vma, endoff = (loff_t)(end - vma->vm_start - 1) + ((loff_t)vma->vm_pgoff << PAGE_SHIFT); - /* vmtruncate_range needs to take i_mutex and i_alloc_sem */ + /* + * Filesystem's fallocate may need to take i_mutex. We need to + * explicitly grab a reference because the vma (and hence the + * vma's reference to the file) can go away as soon as we drop + * mmap_sem. + */ + get_file(f); up_read(¤t->mm->mmap_sem); error = vmtruncate_range(mapping->host, offset, endoff); + fput(f); down_read(¤t->mm->mmap_sem); return error; }