From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:35037) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YalAB-0000dQ-M8 for qemu-devel@nongnu.org; Wed, 25 Mar 2015 09:16:07 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1YalA7-0001wv-GF for qemu-devel@nongnu.org; Wed, 25 Mar 2015 09:16:03 -0400 Received: from mail-wi0-x22d.google.com ([2a00:1450:400c:c05::22d]:38630) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YalA7-0001wr-7k for qemu-devel@nongnu.org; Wed, 25 Mar 2015 09:15:59 -0400 Received: by wibgn9 with SMTP id gn9so38217568wib.1 for ; Wed, 25 Mar 2015 06:15:58 -0700 (PDT) Sender: Paolo Bonzini From: Paolo Bonzini Date: Wed, 25 Mar 2015 14:15:52 +0100 Message-Id: <1427289352-6680-1-git-send-email-pbonzini@redhat.com> Subject: [Qemu-devel] [PATCH] exec: avoid possible overwriting of mmaped area in qemu_ram_remap List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: Gonglei It is not necessary to munmap an area before remapping it with MAP_FIXED; if the memory region specified by addr and len overlaps pages of any existing mapping, then the overlapped part of the existing mapping will be discarded. On the other hand, if QEMU does munmap the pages, there is a small probability that another mmap sneaks in and catches the just-freed portion of the address space. In effect, munmap followed by mmap(MAP_FIXED) is a use-after-free error, and Coverity flags it as such. Fix it. Signed-off-by: Paolo Bonzini --- Please review. :) exec.c | 1 - 1 file changed, 1 deletion(-) diff --git a/exec.c b/exec.c index 8b922db..6d1e1e4 100644 --- a/exec.c +++ b/exec.c @@ -1638,7 +1638,6 @@ void qemu_ram_remap(ram_addr_t addr, ram_addr_t length) abort(); } else { flags = MAP_FIXED; - munmap(vaddr, length); if (block->fd >= 0) { flags |= (block->flags & RAM_SHARED ? MAP_SHARED : MAP_PRIVATE); -- 2.3.3