Don't call fwrite() with len == 0 when writing out relcache init file.

anarazel · anarazel · commit 89a94c24aadd · 2022-03-23T13:13:18.000-07:00
Noticed via -fsanitize=undefined. Backpatch to all branches, for the same reasons as 46ab07f. Discussion: https://postgr.es/m/20220323173537.ll7klrglnp4gn2um@alap3.anarazel.de Backpatch: 10-
diff --git a/src/backend/utils/cache/relcache.c b/src/backend/utils/cache/relcache.c
@@ -6485,7 +6485,7 @@ write_item(const void *data, Size len, FILE *fp)
 {
 	if (fwrite(&len, 1, sizeof(len), fp) != sizeof(len))
 		elog(FATAL, "could not write init file");
-	if (fwrite(data, 1, len, fp) != len)
+	if (len > 0 && fwrite(data, 1, len, fp) != len)
 		elog(FATAL, "could not write init file");
 }
 

Original file line number	Diff line number	Diff line change
`@@ -6485,7 +6485,7 @@ write_item(const void data, Size len, FILE fp)`
`6485`	`6485`	`{`
`6486`	`6486`	`if (fwrite(&len, 1, sizeof(len), fp) != sizeof(len))`
`6487`	`6487`	`elog(FATAL, "could not write init file");`
`6488`		`- if (fwrite(data, 1, len, fp) != len)`
	`6488`	`+ if (len > 0 && fwrite(data, 1, len, fp) != len)`
`6489`	`6489`	`elog(FATAL, "could not write init file");`
`6490`	`6490`	`}`
`6491`	`6491`