[PATCH linux-next] xen/multicall: xen_mc_callback(): avoid buffer overflow

[Tim Gardner]

This buffer overflow was introduced with 
91e0c5f3dad47838cb2ecc1865ce789a0b7182b1
(2.6.24).

Cc: Konrad Rzeszutek Wilk konrad.w...@oracle.com
Cc: Jeremy Fitzhardinge jer...@goop.org
Cc: Thomas Gleixner t...@linutronix.de
Cc: Ingo Molnar mi...@redhat.com
Cc: H. Peter Anvin h...@zytor.com
Cc: x...@kernel.org
Cc: xen-de...@lists.xensource.com
Cc: virtualization@lists.linux-foundation.org
Cc: sta...@vger.kernel.org
Signed-off-by: Tim Gardner tim.gard...@canonical.com
---

This patch applies cleanly to 3.1.10 and newer. Requires a backport
for 2.6.24-3.2.y

 arch/x86/xen/multicalls.c |3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/xen/multicalls.c b/arch/x86/xen/multicalls.c
index 0d82003..5270407 100644
--- a/arch/x86/xen/multicalls.c
+++ b/arch/x86/xen/multicalls.c
@@ -195,9 +195,10 @@ void xen_mc_callback(void (*fn)(void *), void *data)
struct mc_buffer *b = __get_cpu_var(mc_buffer);
struct callback *cb;
 
-   if (b-cbidx == MC_BATCH) {
+   if (b-cbidx = MC_BATCH) {
trace_xen_mc_flush_reason(XEN_MC_FL_CALLBACK);
xen_mc_flush();
+   return;
}
 
trace_xen_mc_callback(fn, data);
-- 
1.7.9.5

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Re: [Xen-devel] [PATCH linux-next] xen/multicall: xen_mc_callback(): avoid buffer overflow

[David Vrabel]

On 08/02/2013 20:34, Tim Gardner wrote:
 This buffer overflow was introduced with 
 91e0c5f3dad47838cb2ecc1865ce789a0b7182b1
 (2.6.24).

There's no buffer overflow here. xen_mc_flush() resets b-cbidx.

David

  arch/x86/xen/multicalls.c |3 ++-
  1 file changed, 2 insertions(+), 1 deletion(-)
 
 diff --git a/arch/x86/xen/multicalls.c b/arch/x86/xen/multicalls.c
 index 0d82003..5270407 100644
 --- a/arch/x86/xen/multicalls.c
 +++ b/arch/x86/xen/multicalls.c
 @@ -195,9 +195,10 @@ void xen_mc_callback(void (*fn)(void *), void *data)
   struct mc_buffer *b = __get_cpu_var(mc_buffer);
   struct callback *cb;
  
 - if (b-cbidx == MC_BATCH) {
 + if (b-cbidx = MC_BATCH) {
   trace_xen_mc_flush_reason(XEN_MC_FL_CALLBACK);
   xen_mc_flush();
 + return;
   }
  
   trace_xen_mc_callback(fn, data);
 

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