Correct off-by-one when reading from pipe

In pg_basebackup.c:reached_end_position(), we're reading from an
internal pipe with our own background process but we're possibly
reading more bytes than will actually fit into our buffer due to
an off-by-one error.  As we're reading from an internal pipe
there's no real risk here, but it's good form to not depend on
such convenient arrangements.

Bug spotted by the Coverity scanner.

Back-patch to 9.2 where this showed up.

diff --git a/src/bin/pg_basebackup/pg_basebackup.c b/src/bin/pg_basebackup/pg_basebackup.c
index 56657a42c4075db4ed5c794cfbf4d2b4938e2f03..a1e12a8aaa331c400529acbd9cbce66d3c5e6396 100644 (file)
--- a/src/bin/pg_basebackup/pg_basebackup.c
+++ b/src/bin/pg_basebackup/pg_basebackup.c
@@ -174,7 +174,7 @@ reached_end_position(XLogRecPtr segendpos, uint32 timeline,
                                                lo;
 
                        MemSet(xlogend, 0, sizeof(xlogend));
-                       r = read(bgpipe[0], xlogend, sizeof(xlogend));
+                       r = read(bgpipe[0], xlogend, sizeof(xlogend)-1);
                        if (r < 0)
                        {
                                fprintf(stderr, _("%s: could not read from ready pipe: %s\n"),