From 68bd348ade453821fd5378479e6718e69bf181f1 Mon Sep 17 00:00:00 2001 From: Stefan Weil Date: Fri, 4 May 2012 08:51:16 +0200 Subject: [PATCH] scsi: Add assertion for use-after-free errors 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 Signed-off-by: Paolo Bonzini --- hw/scsi-bus.c | 1 + 1 file changed, 1 insertion(+) diff --git a/hw/scsi-bus.c b/hw/scsi-bus.c index add1d4f..8ab9bcd 100644 --- a/hw/scsi-bus.c +++ b/hw/scsi-bus.c @@ -1291,6 +1291,7 @@ 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); -- 2.7.4