[PATCH 1/5] hw/char/sclpconsole-lm: avoid guest triggerable assert

[Christian Borntraeger]

If a guest uses incorrect message length it can trigger an assert in
process_mbd which kills the guest instead of reporting an error.  Fix
this by adding the correct length check.

Fixes: 6a444f8507 ("s390/sclplmconsole: Add support for SCLP line-mode console")
Signed-off-by: Christian Borntraeger <borntrae...@linux.ibm.com>
---
 hw/char/sclpconsole-lm.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/hw/char/sclpconsole-lm.c b/hw/char/sclpconsole-lm.c
index 9a16896d22..f6ed282f1b 100644
--- a/hw/char/sclpconsole-lm.c
+++ b/hw/char/sclpconsole-lm.c
@@ -243,7 +243,8 @@ static int write_event_data(SCLPEvent *event, 
EventBufferHeader *ebh)
     SCLPConsoleLM *scon = SCLPLM_CONSOLE(event);
 
     len = be16_to_cpu(data->mdb.header.length);
-    if (len < sizeof(data->mdb.header)) {
+    if (len < sizeof(data->mdb.header) ||
+        len > be16_to_cpu(data->header.length) - sizeof(EventBufferHeader)) {
         return SCLP_RC_INCONSISTENT_LENGTHS;
     }
     len -= sizeof(data->mdb.header);
-- 
2.53.0