Commit 4eb91982 authored Jan 02, 2014 by Rik van Riel Committed by Linus Torvalds Jan 02, 2014

mm: fix use-after-free in sys_remap_file_pages



remap_file_pages calls mmap_region, which may merge the VMA with other
existing VMAs, and free "vma".  This can lead to a use-after-free bug.
Avoid the bug by remembering vm_flags before calling mmap_region, and
not trying to dereference vma later.

Signed-off-by: Rik van Riel <riel@redhat.com>
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Cc: PaX Team <pageexec@freemail.hu>
Cc: Kees Cook <keescook@chromium.org>
Cc: Michel Lespinasse <walken@google.com>
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 3b25df93

mm/fremap.c

+5 −3

Original line number	Diff line number	Diff line
		@@ -208,9 +208,10 @@ get_write_lock:
		if (mapping_cap_account_dirty(mapping)) {
		unsigned long addr;
		struct file *file = get_file(vma->vm_file);
		/* mmap_region may free vma; grab the info now */
		vm_flags = vma->vm_flags;

		addr = mmap_region(file, start, size,
		vma->vm_flags, pgoff);
		addr = mmap_region(file, start, size, vm_flags, pgoff);
		fput(file);
		if (IS_ERR_VALUE(addr)) {
		err = addr;
		@@ -218,7 +219,7 @@ get_write_lock:
		BUG_ON(addr != start);
		err = 0;
		}
		goto out;
		goto out_freed;
		}
		mutex_lock(&mapping->i_mmap_mutex);
		flush_dcache_mmap_lock(mapping);
		@@ -253,6 +254,7 @@ get_write_lock:
		out:
		if (vma)
		vm_flags = vma->vm_flags;
		out_freed:
		if (likely(!has_write_lock))
		up_read(&mm->mmap_sem);
		else

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