From d3ba5dcfd4f21e27c4ead7bde29374e66764179c Mon Sep 17 00:00:00 2001
From: Markus Mittendrein <git@maxmitti.tk>
Date: Sat, 31 Aug 2019 13:51:07 +0200
Subject: use a temporary file in saveOverwrite to avoid possible data loss in
 error cases (fixes SIGBUS in c4touch)

---
 src/cc4group.c | 75 +++++++++++++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 61 insertions(+), 14 deletions(-)

diff --git a/src/cc4group.c b/src/cc4group.c
index 93dbd3d..b086110 100644
--- a/src/cc4group.c
+++ b/src/cc4group.c
@@ -388,15 +388,30 @@ static void* cc4group_mapSizedWriteFd(CC4Group* const this, int fd, size_t size)
 }
 
 static const char tmpFileTemplate[] = "cc4grouptmpXXXXXX";
+#define tmpFileNameLength (sizeof(tmpFileTemplate) / sizeof(tmpFileTemplate[0]))
 
 typedef struct {
 	void* addr;
 	size_t size;
-	char fileName[sizeof(tmpFileTemplate) / sizeof(tmpFileTemplate[0])];
+	char fileName[tmpFileNameLength];
 	bool unlinkLater;
 	const CC4Group* group;
 } MunmapData;
 
+// *fileNameTarget must be at least tmpFileNameLength long!
+static int cc4group_createTmpFile(CC4Group* const this, char* const fileNameTarget)
+{
+	strncpy(fileNameTarget, tmpFileTemplate, tmpFileNameLength);
+	int tmpFile = mkstemp(fileNameTarget);
+	if(tmpFile == -1)
+	{
+		SET_ERRNO_ERROR("mkstemp: Creating and opening the tmp file");
+		fileNameTarget[0] = '\0';
+	}
+
+	return tmpFile;
+}
+
 static void cc4group_tryWarnUnlink(const CC4Group* const this, const char* const fileName)
 {
 	if(unlink(fileName) == -1)
@@ -430,14 +445,10 @@ static void* cc4group_createTmpMemoryFile(CC4Group* const this, const size_t siz
 		return NULL;
 	}
 
-	strncpy(unmapData->fileName, tmpFileTemplate, sizeof(unmapData->fileName) / sizeof(unmapData->fileName[0]));
-
 	void* ret = NULL;
-	int tmpFile = mkstemp(unmapData->fileName);
+	int tmpFile = cc4group_createTmpFile(this, unmapData->fileName);
 	if(tmpFile == -1)
 	{
-		SET_ERRNO_ERROR("mkstemp: Creating and opening the tmp file");
-		unmapData->fileName[0] = '\0';
 		goto ret;
 	}
 
@@ -2586,7 +2597,7 @@ static bool cc4group_saveToFd(CC4Group* const this, int fd)
 	return cc4group_saveWithWriteCallback(this, cc4group_writeToFdCallback, &fd, 0);
 }
 
-static bool cc4group_saveIt(CC4Group* const this, const char* const path, bool const overwrite)
+static bool cc4group_save(CC4Group* const this, const char* const path)
 {
 	assert(this);
 	assert(path);
@@ -2598,7 +2609,7 @@ static bool cc4group_saveIt(CC4Group* const this, const char* const path, bool c
 	}
 
 	bool success = false;
-	int file = open(path, O_WRONLY | O_BINARY | O_CREAT | (overwrite ? O_TRUNC : O_EXCL), 0644);
+	int file = open(path, O_WRONLY | O_BINARY | O_CREAT | O_EXCL, 0644);
 
 	if(file == -1)
 	{
@@ -2627,14 +2638,50 @@ static bool cc4group_saveIt(CC4Group* const this, const char* const path, bool c
 	return success;
 }
 
-static bool cc4group_save(CC4Group* const this, const char* const path)
-{
-	return cc4group_saveIt(this, path, false);
-}
-
 static bool cc4group_saveOverwrite(CC4Group* const this, const char* const path)
 {
-	return cc4group_saveIt(this, path, true);
+	if(strcmp(path, "-") == 0)
+	{
+		return cc4group_save(this, path);
+	}
+
+	char tmpFileName[tmpFileNameLength];
+	int tmpFile = cc4group_createTmpFile(this, tmpFileName);
+
+	if(tmpFile == -1)
+	{
+		return false;
+	}
+
+	bool success = false;
+	if(!cc4group_saveWithWriteCallback(this, cc4group_writeToFdCallback, &tmpFile, 0))
+	{
+		goto ret;
+	}
+
+	if(rename(tmpFileName, path) == 0)
+	{
+		success = true;
+	}
+	else
+	{
+		SET_ERRNO_ERROR("rename: can't rename the temporary file to the target path");
+	}
+
+	if(close(tmpFile) == -1)
+	{
+		cc4group_warn(this, "close: Closing the target group file failed: %s", strerror(errno));
+	}
+
+ret:
+	if(!success)
+	{
+		if(unlink(tmpFileName) == -1)
+		{
+			cc4group_warn(this, "unlink: Deleting the incomplete temporary group file \"%s\" failed: %s", tmpFileName, strerror(errno));
+		}
+	}
+	return success;
 }
 
 static bool cc4group_getEntryInfoForEntry(CC4Group* const this, const C4GroupEntryData* const entry, CC4Group_EntryInfo* const info, bool const lazy)
-- 
cgit v1.2.3-54-g00ecf