[xen master] tools/xl: vcpu-pin: Skip global affinity when the hard affinity is not changed

[patchbot@xxxxxxx]

commit 3748c81fa1ff5e67c0442978c583e722820b1690
Author:     Julien Grall <jgrall@xxxxxxxxxx>
AuthorDate: Thu Apr 30 11:20:44 2020 +0100
Commit:     Julien Grall <jgrall@xxxxxxxxxx>
CommitDate: Mon May 11 10:18:22 2020 +0100

    tools/xl: vcpu-pin: Skip global affinity when the hard affinity is not 
changed
    
    After XSA-273, it is not possible to modify the vCPU soft affinity using
    xl vcpu-pin without modifying the hard affinity. Instead the command
    will crash.
    
    42sh> gdb /usr/local/sbin/xl
    (gdb) r vcpu-pin 0 0 - 10
    [...]
    Program received signal SIGSEGV, Segmentation fault.
    [...]
    (gdb) bt
    
    This is happening because 'xl' will use NULL when an affinity doesn't
    need to be modified. However, we will still try to apply the global
    affinity in the this case.
    
    As the hard affinity is not changed, then we don't need to apply the
    global affinity. So skip it when hard is NULL.
    
    Backport: 4.6+ # Any release with XSA-273
    Fixes: aa67b97ed342 ("xl.conf: Add global affinity masks")
    Reported-by: Pawel Wieczorkiewicz <wipawel@xxxxxxxxx>
    Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>
    Acked-by: Wei Liu <wl@xxxxxxx>
---
 tools/xl/xl_vcpu.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/xl/xl_vcpu.c b/tools/xl/xl_vcpu.c
index 9ff5354f74..66877a57de 100644
--- a/tools/xl/xl_vcpu.c
+++ b/tools/xl/xl_vcpu.c
@@ -283,7 +283,7 @@ int main_vcpupin(int argc, char **argv)
     }
 
     /* Only hard affinity matters here */
-    if (!ignore_masks) {
+    if (!ignore_masks && hard) {
         libxl_dominfo dominfo;
 
         if (libxl_domain_info(ctx, &dominfo, domid)) {
--
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