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Commit 4eb91982 authored by Rik van Riel's avatar Rik van Riel Committed by Linus Torvalds
Browse files

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: default avatarRik van Riel <riel@redhat.com>
Reported-by: default avatarDmitry 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 3b25df93

mm/fremap.c

+5 −3
Original line number Diff line number Diff line
@@ -208,9 +208,10 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size, 
		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 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size, 
				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 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size, 
out:

	if (vma)

		vm_flags = vma->vm_flags;

out_freed:

	if (likely(!has_write_lock))

		up_read(&mm->mmap_sem);

	else