Fix incorrect calculation in shm_mq_receive.

If some, but not all, of the length word has already been read, and the
next attempt to read sees exactly the number of bytes needed to complete
the length word, or fewer, then we'll incorrectly read less than all of
the available data.

Antonin Houska

diff --git a/src/backend/storage/ipc/shm_mq.c b/src/backend/storage/ipc/shm_mq.c
index 126cb0751b316490724dae1231c719ba044f4cdc..e765cea5aaa4e090d37b47b71a1df59c98cc979b 100644 (file)
--- a/src/backend/storage/ipc/shm_mq.c
+++ b/src/backend/storage/ipc/shm_mq.c
@@ -584,7 +584,7 @@ shm_mq_receive(shm_mq_handle *mqh, Size *nbytesp, void **datap, bool nowait)
                        if (mqh->mqh_partial_bytes + rb > sizeof(Size))
                                lengthbytes = sizeof(Size) - mqh->mqh_partial_bytes;
                        else
-                               lengthbytes = rb - mqh->mqh_partial_bytes;
+                               lengthbytes = rb;
                        memcpy(&mqh->mqh_buffer[mqh->mqh_partial_bytes], rawdata,
                                   lengthbytes);
                        mqh->mqh_partial_bytes += lengthbytes;