From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:59712) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1SPzx6-0002HR-6Z for qemu-devel@nongnu.org; Thu, 03 May 2012 13:36:29 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1SPzx4-0002Zy-6Z for qemu-devel@nongnu.org; Thu, 03 May 2012 13:36:27 -0400 Received: from v220110690675601.yourvserver.net ([78.47.199.172]:59790) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1SPzx4-0002ZG-02 for qemu-devel@nongnu.org; Thu, 03 May 2012 13:36:26 -0400 From: Stefan Weil Date: Thu, 3 May 2012 19:36:23 +0200 Message-Id: <1336066583-10503-1-git-send-email-sw@weilnetz.de> Subject: [Qemu-devel] [PATCH 1.1] scsi: Add assertion for use-after-free errors List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: Paolo Bonzini , Anthony Liguori , Paul Brook , Stefan Weil The QEMU emulation which is currently used with Raspberry PI images (qemu-system-arm -M versatilepb ...) accesses memory which was freed. Valgrind output (extract): ==17857== Invalid write of size 4 ==17857== at 0x24EB06: scsi_req_unref (scsi-bus.c:1273) ==17857== by 0x24FFAE: scsi_read_complete (scsi-disk.c:277) ==17857== by 0x152ACC: bdrv_co_em_bh (block.c:3363) ==17857== by 0x13D49C: qemu_bh_poll (async.c:71) ==17857== by 0x211A8C: main_loop_wait (main-loop.c:503) ==17857== by 0x207954: main_loop (vl.c:1555) ==17857== by 0x20E9C9: main (vl.c:3653) ==17857== Address 0x1c54383c is 12 bytes inside a block of size 260 free'd ==17857== at 0x4824B3A: free (vg_replace_malloc.c:366) ==17857== by 0x20ADFA: free_and_trace (vl.c:2250) ==17857== by 0x4899FC5: g_free (in /lib/libglib-2.0.so.0.2400.1) ==17857== by 0x24EB3B: scsi_req_unref (scsi-bus.c:1277) ==17857== by 0x24F003: scsi_req_complete (scsi-bus.c:1383) ==17857== by 0x25022A: scsi_read_data (scsi-disk.c:334) ==17857== by 0x24EB9F: scsi_req_continue (scsi-bus.c:1289) ==17857== by 0x1C7787: lsi_do_dma (lsi53c895a.c:575) ==17857== by 0x1C8CDA: lsi_execute_script (lsi53c895a.c:1147) ==17857== by 0x1C74EA: lsi_resume_script (lsi53c895a.c:510) ==17857== by 0x1C7ECD: lsi_transfer_data (lsi53c895a.c:746) ==17857== by 0x24EC90: scsi_req_data (scsi-bus.c:1307) (There are some more similar messages.) This patch adds an assertion which also detects those errors: Calling scsi_req_unref is not allowed when the previous call of that function has decremented refcount to 0, because in this case req was freed. Signed-off-by: Stefan Weil --- There are chances that this patch breaks some test scenarios, but that is intentional: we should not pretend that there are no errors when there are some. The Raspberry PI emulation with QEMU is currently used by a lot of people. Please apply this patch for the tests of QEMU 1.1. Of course we should also fix the problem which triggers the assertion. I still don't know whether it is caused by lsi53c895a.c or by the scsi code. Thanks, Stefan Weil hw/scsi-bus.c | 1 + 1 files changed, 1 insertions(+), 0 deletions(-) diff --git a/hw/scsi-bus.c b/hw/scsi-bus.c index dbdb99c..62779c7 100644 --- a/hw/scsi-bus.c +++ b/hw/scsi-bus.c @@ -1270,6 +1270,7 @@ SCSIRequest *scsi_req_ref(SCSIRequest *req) void scsi_req_unref(SCSIRequest *req) { + assert(req->refcount > 0); if (--req->refcount == 0) { if (req->ops->free_req) { req->ops->free_req(req); -- 1.7.9