[Qemu-devel] [PATCH] blockdev: check dinfo ptr before using

[Ryan Harper <ryanh@us.ibm.com>]

If a user decides to punish a guest by revoking its block device via
drive_del, and subsequently also attempts to remove the pci device
backing it, and the device is using blockdev_auto_del() then we get a
segfault when we attempt to access dinfo->auto_del.[1]

The fix is to check if drive_get_by_blockdev() actually returns a valid
dinfo pointer or not.

1. (qemu) pci_add auto storage file=images/test01.raw,if=virtio,id=block1,snapshot=on
   (qemu) drive_del block1
   (qemu) pci_del 5
   *segfault*

Signed-off-by: Ryan Harper <ryanh@us.ibm.com>

-- 
Ryan Harper
Software Engineer; Linux Technology Center
IBM Corp., Austin, Tx
ryanh@us.ibm.com


diff --git a/blockdev.c b/blockdev.c
index f6ac439..3b3b82d 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -30,14 +30,16 @@ void blockdev_mark_auto_del(BlockDriverState *bs)
 {
     DriveInfo *dinfo = drive_get_by_blockdev(bs);
 
-    dinfo->auto_del = 1;
+    if (dinfo) {
+        dinfo->auto_del = 1;
+    }
 }
 
 void blockdev_auto_del(BlockDriverState *bs)
 {
     DriveInfo *dinfo = drive_get_by_blockdev(bs);
 
-    if (dinfo->auto_del) {
+    if (dinfo && dinfo->auto_del) {
         drive_uninit(dinfo);
     }
 }