From 9ab4233dd08036fe34a89c7dc6f47a8bf2eb29eb Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Thu, 5 Jul 2012 16:00:11 -0700 Subject: [PATCH] mm: Hold a file reference in madvise_remove 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 --- mm/madvise.c | 18 ++++++++++++++---- 1 file changed, 14 insertions(+), 4 deletions(-) diff --git a/mm/madvise.c b/mm/madvise.c index deff1b64a08c..14d260fa0d17 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -15,6 +15,7 @@ #include #include #include +#include /* * Any behaviour which results in changes to the vma->vm_flags needs to @@ -204,14 +205,16 @@ static long madvise_remove(struct vm_area_struct *vma, { loff_t offset; 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; } @@ -221,11 +224,18 @@ static long madvise_remove(struct vm_area_struct *vma, offset = (loff_t)(start - vma->vm_start) + ((loff_t)vma->vm_pgoff << PAGE_SHIFT); - /* filesystem's fallocate may need to take i_mutex */ + /* + * 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 = do_fallocate(vma->vm_file, + error = do_fallocate(f, FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE, offset, end - start); + fput(f); down_read(¤t->mm->mmap_sem); return error; } -- 2.20.1