Fix corner cases in readlink() usage.

Make sure all calls are protected by HAVE_READLINK, and get the buffer
overflow tests right.  Be a bit more paranoid about string length in
_tarWriteHeader(), too.

Author: tglsfdc

src/backend/replication/basebackup.c

@@ -46,7 +46,7 @@ static int64 sendDir(char *path, int basepathlen, bool sizeonly);
 static void sendFile(char *readfilename, char *tarfilename,
 		 struct stat * statbuf);
 static void sendFileWithContent(const char *filename, const char *content);
-static void _tarWriteHeader(const char *filename, char *linktarget,
+static void _tarWriteHeader(const char *filename, const char *linktarget,
 				struct stat * statbuf);
 static void send_int8_string(StringInfoData *buf, int64 intval);
 static void SendBackupHeader(List *tablespaces);
@@ -117,17 +117,19 @@ perform_base_backup(basebackup_options *opt, DIR *tblspcdir)
 			snprintf(fullpath, sizeof(fullpath), "pg_tblspc/%s", de->d_name);
 
 #if defined(HAVE_READLINK) || defined(WIN32)
-			rllen = readlink(fullpath, linkpath, sizeof(linkpath) - 1);
+			rllen = readlink(fullpath, linkpath, sizeof(linkpath));
 			if (rllen < 0)
 			{
 				ereport(WARNING,
-						(errmsg("could not read symbolic link \"%s\": %m", fullpath)));
+						(errmsg("could not read symbolic link \"%s\": %m",
+								fullpath)));
 				continue;
 			}
 			else if (rllen >= sizeof(linkpath))
 			{
 				ereport(WARNING,
-						(errmsg("symbolic link \"%s\" target is too long", fullpath)));
+						(errmsg("symbolic link \"%s\" target is too long",
+								fullpath)));
 				continue;
 			}
 			linkpath[rllen] = '\0';
@@ -139,9 +141,9 @@ perform_base_backup(basebackup_options *opt, DIR *tblspcdir)
 			tablespaces = lappend(tablespaces, ti);
 #else
 			/*
-			 * If the platform does not have symbolic links, it should not be possible
-			 * to have tablespaces - clearly somebody else created them. Warn about it
-			 * and ignore.
+			 * If the platform does not have symbolic links, it should not be
+			 * possible to have tablespaces - clearly somebody else created
+			 * them. Warn about it and ignore.
 			 */
 			ereport(WARNING,
 					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
@@ -635,24 +637,45 @@ sendDir(char *path, int basepathlen, bool sizeonly)
 			continue;			/* don't recurse into pg_xlog */
 		}
 
+		/* Allow symbolic links in pg_tblspc only */
+		if (strcmp(path, "./pg_tblspc") == 0 &&
 #ifndef WIN32
-		if (S_ISLNK(statbuf.st_mode) && strcmp(path, "./pg_tblspc") == 0)
+				 S_ISLNK(statbuf.st_mode)
 #else
-		if (pgwin32_is_junction(pathbuf) && strcmp(path, "./pg_tblspc") == 0)
+				 pgwin32_is_junction(pathbuf)
 #endif
+			)
 		{
-			/* Allow symbolic links in pg_tblspc */
+#if defined(HAVE_READLINK) || defined(WIN32)
 			char		linkpath[MAXPGPATH];
+			int			rllen;
 
-			MemSet(linkpath, 0, sizeof(linkpath));
-			if (readlink(pathbuf, linkpath, sizeof(linkpath) - 1) == -1)
+			rllen = readlink(pathbuf, linkpath, sizeof(linkpath));
+			if (rllen < 0)
 				ereport(ERROR,
 						(errcode_for_file_access(),
 						 errmsg("could not read symbolic link \"%s\": %m",
 								pathbuf)));
+			if (rllen >= sizeof(linkpath))
+				ereport(ERROR,
+						(errmsg("symbolic link \"%s\" target is too long",
+								pathbuf)));
+			linkpath[rllen] = '\0';
+
 			if (!sizeonly)
 				_tarWriteHeader(pathbuf + basepathlen + 1, linkpath, &statbuf);
 			size += 512;		/* Size of the header just added */
+#else
+			/*
+			 * If the platform does not have symbolic links, it should not be
+			 * possible to have tablespaces - clearly somebody else created
+			 * them. Warn about it and ignore.
+			 */
+			ereport(WARNING,
+					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+					 errmsg("tablespaces are not supported on this platform")));
+			continue;
+#endif /* HAVE_READLINK */
 		}
 		else if (S_ISDIR(statbuf.st_mode))
 		{
@@ -800,7 +823,8 @@ sendFile(char *readfilename, char *tarfilename, struct stat * statbuf)
 
 
 static void
-_tarWriteHeader(const char *filename, char *linktarget, struct stat * statbuf)
+_tarWriteHeader(const char *filename, const char *linktarget,
+				struct stat * statbuf)
 {
 	char		h[512];
 	int			lastSum = 0;
@@ -848,7 +872,7 @@ _tarWriteHeader(const char *filename, char *linktarget, struct stat * statbuf)
 	{
 		/* Type - Symbolic link */
 		sprintf(&h[156], "2");
-		strcpy(&h[157], linktarget);
+		sprintf(&h[157], "%.99s", linktarget);
 	}
 	else if (S_ISDIR(statbuf->st_mode))
 		/* Type - directory */