From 4642e4e0b0a63d9da6ac4479963dec6c7b71ac68 Mon Sep 17 00:00:00 2001 From: Andrew Klychkov Date: Wed, 3 Sep 2025 10:48:49 +0200 Subject: [PATCH] Fix ALTER SYSTEM empty string bug for GUC_LIST_QUOTE parameters When ALTER SYSTEM SET is used with an empty string for parameters with GUC_LIST_QUOTE flag (like shared_preload_libraries), the empty string was being double-quoted, resulting in '""' being written to postgresql.auto.conf. This caused server crashes on restart due to malformed configuration syntax. The fix detects when a GUC_LIST_QUOTE parameter has the value '""' and writes it as '' instead, preventing the double-quoting issue while maintaining proper configuration file syntax. Fixes bug where 'ALTER SYSTEM SET "shared_preload_libraries" TO ''' would write 'shared_preload_libraries = '""'' to postgresql.auto.conf. --- src/backend/utils/misc/guc.c | 39 ++++++++++++++++++++++++++++++++++++ 1 file changed, 39 insertions(+) diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c index 46fdefebe3..7494cbd56b 100644 --- a/src/backend/utils/misc/guc.c +++ b/src/backend/utils/misc/guc.c @@ -4497,6 +4497,45 @@ write_auto_conf_file(int fd, const char *filename, ConfigVariable *head) for (item = head; item != NULL; item = item->next) { char *escaped; + bool is_guc_list_quote = false; + + /* + * Check if this is a GUC_LIST_QUOTE parameter to handle empty strings + * specially and prevent double-quoting issues. + */ + if (item->value[0] == '\0' || strcmp(item->value, "\"\"") == 0) + { + struct config_generic *record = find_option(item->name, false, true, WARNING); + if (record && (record->flags & GUC_LIST_QUOTE)) + is_guc_list_quote = true; + } + + /* + * Special handling for GUC_LIST_QUOTE parameters with empty strings. + * When ALTER SYSTEM SET is used with an empty string for such parameters, + * the value comes through as '""' (quoted empty string). We want to write + * this as an empty string rather than the quoted version to avoid the + * double-quoting issue. + */ + if (is_guc_list_quote && (item->value[0] == '\0' || strcmp(item->value, "\"\"") == 0)) + { + /* For GUC_LIST_QUOTE parameters, write empty string as '' */ + resetStringInfo(&buf); + appendStringInfoString(&buf, item->name); + appendStringInfoString(&buf, " = ''\n"); + + errno = 0; + if (write(fd, buf.data, buf.len) != buf.len) + { + /* if write didn't set errno, assume problem is no disk space */ + if (errno == 0) + errno = ENOSPC; + ereport(ERROR, + (errcode_for_file_access(), + errmsg("could not write to file \"%s\": %m", filename))); + } + continue; + } resetStringInfo(&buf); -- 2.47.0