Fix sscanf limits in pg_basebackup and pg_dump

danielgustafsson · danielgustafsson · commit 57bf8f7b75ec · 2021-10-19T12:59:50.000+02:00
Make sure that the string parsing is limited by the size of the destination buffer. In pg_basebackup the available values sent from the server is limited to two characters so there was no risk of overflow. In pg_dump the buffer is bounded by MAXPGPATH, and thus the limit must be inserted via preprocessor expansion and the buffer increased by one to account for the terminator. There is no risk of overflow here, since in this case, the buffer scanned is smaller than the destination buffer. Backpatch the pg_basebackup fix to 11 where it was introduced, and the pg_dump fix all the way down to 9.6. Reviewed-by: Tom Lane Discussion: https://postgr.es/m/B14D3D7B-F98C-4E20-9459-C122C67647FB@yesql.se Backpatch-through: 11 and 9.6
diff --git a/src/bin/pg_basebackup/streamutil.c b/src/bin/pg_basebackup/streamutil.c
@@ -311,7 +311,7 @@ RetrieveWalSegSize(PGconn *conn)
 	}
 
 	/* fetch xlog value and unit from the result */
-	if (sscanf(PQgetvalue(res, 0, 0), "%d%s", &xlog_val, xlog_unit) != 2)
+	if (sscanf(PQgetvalue(res, 0, 0), "%d%2s", &xlog_val, xlog_unit) != 2)
 	{
 		pg_log_error("WAL segment size could not be parsed");
 		PQclear(res);
diff --git a/src/bin/pg_dump/pg_backup_directory.c b/src/bin/pg_dump/pg_backup_directory.c
@@ -451,11 +451,11 @@ _LoadBlobs(ArchiveHandle *AH)
 	/* Read the blobs TOC file line-by-line, and process each blob */
 	while ((cfgets(ctx->blobsTocFH, line, MAXPGPATH)) != NULL)
 	{
-		char		fname[MAXPGPATH];
+		char		fname[MAXPGPATH + 1];
 		char		path[MAXPGPATH];
 
 		/* Can't overflow because line and fname are the same length. */
-		if (sscanf(line, "%u %s\n", &oid, fname) != 2)
+		if (sscanf(line, "%u %" CppAsString2(MAXPGPATH) "s\n", &oid, fname) != 2)
 			fatal("invalid line in large object TOC file \"%s\": \"%s\"",
 				  fname, line);
 

Original file line number	Diff line number	Diff line change
`@@ -311,7 +311,7 @@ RetrieveWalSegSize(PGconn *conn)`
`311`	`311`	`}`
`312`	`312`
`313`	`313`	`/* fetch xlog value and unit from the result */`
`314`		`- if (sscanf(PQgetvalue(res, 0, 0), "%d%s", &xlog_val, xlog_unit) != 2)`
	`314`	`+ if (sscanf(PQgetvalue(res, 0, 0), "%d%2s", &xlog_val, xlog_unit) != 2)`
`315`	`315`	`{`
`316`	`316`	`pg_log_error("WAL segment size could not be parsed");`
`317`	`317`	`PQclear(res);`