[PULL 23/26] migration: Fix migration_channel_read_peek() error path

[peterx]

From: Avihai Horon <avihaih@nvidia.com>

migration_channel_read_peek() calls qio_channel_readv_full() and handles
both cases of return value == 0 and return value < 0 the same way, by
calling error_setg() with errp. However, if return value < 0, errp is
already set, so calling error_setg() with errp will lead to an assert.

Fix it by handling these cases separately, calling error_setg() with
errp only in return value == 0 case.

Fixes: 6720c2b32725 ("migration: check magic value for deciding the mapping of 
channels")
Signed-off-by: Avihai Horon <avihaih@nvidia.com>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Link: https://lore.kernel.org/r/20231231093016.14204-10-avihaih@nvidia.com
Signed-off-by: Peter Xu <peterx@redhat.com>
---
 migration/channel.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/migration/channel.c b/migration/channel.c
index ca3319a309..f9de064f3b 100644
--- a/migration/channel.c
+++ b/migration/channel.c
@@ -117,9 +117,12 @@ int migration_channel_read_peek(QIOChannel *ioc,
         len = qio_channel_readv_full(ioc, &iov, 1, NULL, NULL,
                                      QIO_CHANNEL_READ_FLAG_MSG_PEEK, errp);
 
-        if (len <= 0 && len != QIO_CHANNEL_ERR_BLOCK) {
-            error_setg(errp,
-                       "Failed to peek at channel");
+        if (len < 0 && len != QIO_CHANNEL_ERR_BLOCK) {
+            return -1;
+        }
+
+        if (len == 0) {
+            error_setg(errp, "Failed to peek at channel");
             return -1;
         }
 
-- 
2.41.0