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Re: [libvirt] [PATCH 1/2] qemu: caps: Fix segfault on daemon startup



On 01/27/2012 11:34 AM, Cole Robinson wrote:
> On my f16 box at least, this tries to free p unconditionally which isn't
> always okay, 'p' is freeable only under a limited scope.

You must not have yajl-devel installed.  No wonder I didn't see that I
had introduced a regression.

> ---
>  src/qemu/qemu_capabilities.c |    3 +--
>  1 files changed, 1 insertions(+), 2 deletions(-)
> 
> diff --git a/src/qemu/qemu_capabilities.c b/src/qemu/qemu_capabilities.c
> index 6dee9d8..5487ecd 100644
> --- a/src/qemu/qemu_capabilities.c
> +++ b/src/qemu/qemu_capabilities.c
> @@ -1336,10 +1336,9 @@ fail:
>      qemuReportError(VIR_ERR_INTERNAL_ERROR,
>                      _("cannot parse %s version number in '%s'"),
>                      qemu, p ? p : help);
> -
> -cleanup:
>      VIR_FREE(p);
>  
> +cleanup:

Yuck.  Why are we even calling strndup in the first place, just to
produce a nicer error message?  I'm pushing this instead.

From ab6f1c9814f88e0547a5567176282f501fb138e2 Mon Sep 17 00:00:00 2001
From: Eric Blake <eblake redhat com>
Date: Fri, 27 Jan 2012 13:53:11 -0700
Subject: [PATCH] qemu: avoid double free of qemu help output

If yajl was not compiled in, we end up freeing an incoming
parameter, which leads to a bogus free later on.  Regression
introduced in commit 6e769eb.

* src/qemu/qemu_capabilities.c (qemuCapsParseHelpStr): Avoid alloc
on failure path, which in turn fixes bogus free.
Reported by Cole Robinson.
---
 src/qemu/qemu_capabilities.c |   10 ++++------
 1 files changed, 4 insertions(+), 6 deletions(-)

diff --git a/src/qemu/qemu_capabilities.c b/src/qemu/qemu_capabilities.c
index 6dee9d8..426637c 100644
--- a/src/qemu/qemu_capabilities.c
+++ b/src/qemu/qemu_capabilities.c
@@ -1330,16 +1330,14 @@ int qemuCapsParseHelpStr(const char *qemu,

 fail:
     p = strchr(help, '\n');
-    if (p)
-        p = strndup(help, p - help);
+    if (!p)
+        p = strchr(help, '\0');

     qemuReportError(VIR_ERR_INTERNAL_ERROR,
-                    _("cannot parse %s version number in '%s'"),
-                    qemu, p ? p : help);
+                    _("cannot parse %s version number in '%.*s'"),
+                    qemu, (int) (p - help), help);

 cleanup:
-    VIR_FREE(p);
-
     return -1;
 }

-- 
1.7.7.6



-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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