Mailing List Archive

commit e96cdba338e9f14e745a2725f181f5deec848b55
Author: Julien Grall <jgrall@amazon.com>
AuthorDate: Tue Jul 7 15:18:59 2020 +0200
Commit: Jan Beulich <jbeulich@suse.com>
CommitDate: Tue Jul 7 15:18:59 2020 +0200

xen/common: event_channel: Don't ignore error in get_free_port()

Currently, get_free_port() is assuming that the port has been allocated
when evtchn_allocate_port() is not return -EBUSY.

However, the function may return an error when:
- We exhausted all the event channels. This can happen if the limit
configured by the administrator for the guest ('max_event_channels'
in xl cfg) is higher than the ABI used by the guest. For instance,
if the guest is using 2L, the limit should not be higher than 4095.
- We cannot allocate memory (e.g Xen has not more memory).

Users of get_free_port() (such as EVTCHNOP_alloc_unbound) will validly
assuming the port was valid and will next call evtchn_from_port(). This
will result to a crash as the memory backing the event channel structure
is not present.

Fixes: 368ae9a05fe ("xen/pvshim: forward evtchn ops between L0 Xen and L2 DomU")
Signed-off-by: Julien Grall <jgrall@amazon.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
master commit: 2e9c2bc292231823a3a021d2e0a9f1956bf00b3c
master date: 2020-07-07 14:35:36 +0200
---
xen/common/event_channel.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/xen/common/event_channel.c b/xen/common/event_channel.c
index c62046590b..c692bd2175 100644
--- a/xen/common/event_channel.c
+++ b/xen/common/event_channel.c
@@ -195,10 +195,10 @@ static int get_free_port(struct domain *d)
{
int rc = evtchn_allocate_port(d, port);

- if ( rc == -EBUSY )
- continue;
-
- return port;
+ if ( rc == 0 )
+ return port;
+ else if ( rc != -EBUSY )
+ return rc;
}

return -ENOSPC;
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.11