From eeaae2e758a4ab0fd889d95331129ad300c25a52 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Javier=20Jaramago=20Fern=C3=A1ndez?=
 <jaramago.fernandez.javier@gmail.com>
Date: Fri, 12 Jul 2024 18:54:53 +0200
Subject: [PATCH] Make 'proxy_debug_func' saves/restore 'errno'

Several calls inside 'proxy_debug_func' (specially if database logging
is enabled) could alter 'errno', which could influence error handling.
---
 include/proxysql.h |  4 ++++
 lib/debug.cpp      | 13 +++++++++++--
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/include/proxysql.h b/include/proxysql.h
index 90c881d414..8b6d1d4d50 100644
--- a/include/proxysql.h
+++ b/include/proxysql.h
@@ -117,6 +117,10 @@ void proxy_info_(const char* msg, ...);
 #ifdef DEBUG
 void init_debug_struct();
 void init_debug_struct_from_cmdline();
+/**
+ * @brief Add a debug entry in the error log. To be used through 'proxy_debug' macro.
+ * @details This function saves/restores the previous 'errno' value.
+ */
 __attribute__((__format__ (__printf__, 7, 8)))
 void proxy_debug_func(enum debug_module, int, int, const char *, int, const char *, const char *, ...);
 void proxy_debug_get_filters(std::set<std::string>&);
diff --git a/lib/debug.cpp b/lib/debug.cpp
index e4eda648f5..4f3755c9c0 100644
--- a/lib/debug.cpp
+++ b/lib/debug.cpp
@@ -131,15 +131,22 @@ void proxy_debug_load_filters(std::set<std::string>& f) {
 	//pthread_mutex_unlock(&debug_mutex);
 }
 
+// REMINDER: This function should always save/restore 'errno', otherwise it could influence error handling.
 void proxy_debug_func(enum debug_module module, int verbosity, int thr, const char *__file, int __line, const char *__func, const char *fmt, ...) {
+	int saved_errno = errno;
 	assert(module<PROXY_DEBUG_UNKNOWN);
 	if (pretime == 0) { // never initialized
 		pretime=realtime_time();
 	}
-	if (GloVars.global.gdbg_lvl[module].verbosity < verbosity)
+	if (GloVars.global.gdbg_lvl[module].verbosity < verbosity) {
+		errno = saved_errno;
 		return;
-	if (filter_debug_entry(__file, __line, __func)) // check if the entry must be filtered
+	}
+	// check if the entry must be filtered
+	if (filter_debug_entry(__file, __line, __func)) {
+		errno = saved_errno;
 		return;
+	}
 	char origdebugbuff[DEBUG_MSG_MAXSIZE];
 	char debugbuff[DEBUG_MSG_MAXSIZE];
 	char longdebugbuff[DEBUG_MSG_MAXSIZE*8];
@@ -243,6 +250,8 @@ void proxy_debug_func(enum debug_module module, int verbosity, int thr, const ch
 	pthread_mutex_unlock(&debug_mutex);
 	if (curtime != 0)
 		pretime=curtime;
+
+	errno = saved_errno;
 };
 #endif