coroutine: Fix use after free with qemu_coroutine_yield()

Instead of using the same function for entering and exiting coroutines,
and hoping that it doesn't add any functionality that hurts with the
parameters used for exiting, we can just directly call into the real
task switch in qemu_coroutine_switch().

This fixes a use-after-free scenario where reentering a coroutine that
has yielded still accesses the old parent coroutine (which may have
meanwhile terminated) in the part of coroutine_swap() that follows
qemu_coroutine_switch().

Cc: qemu-stable@nongnu.org
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
(cherry picked from commit 80687b4dd6f43b3fef61fef8fbcb358457350562)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

diff --git a/qemu-coroutine.c b/qemu-coroutine.c
index bd574aa1b57123acbc2b32300af8cb9d0248aa94..0101855e6573fb39e81d5ac5426a8ca5170012a6 100644 (file)
--- a/qemu-coroutine.c
+++ b/qemu-coroutine.c
@@ -135,7 +135,7 @@ void coroutine_fn qemu_coroutine_yield(void)
     }
 
     self->caller = NULL;
-    coroutine_swap(self, to);
+    qemu_coroutine_switch(self, to, COROUTINE_YIELD);
 }
 
 void qemu_coroutine_adjust_pool_size(int n)