From 2f40a49c022377973fefa23bdf4ecfe8586aae54 Mon Sep 17 00:00:00 2001
From: Thomas Debesse <dev@illwieckz.net>
Date: Thu, 25 Feb 2021 02:12:23 +0100
Subject: [PATCH] q3map2: implement symlink resolution
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Ported from Dæmon engine implementation by slipher
which was a complete rewrite of one I did on Dæmon
by taking inspiration from Darkplaces engine.

- https://github.com/DaemonEngine/Daemon/blob/master/src/common/FileSystem.cpp
- https://gitlab.com/xonotic/darkplaces/-/blob/div0-stable/fs.c
---
 tools/quake3/common/vfs.c | 89 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 89 insertions(+)

diff --git a/tools/quake3/common/vfs.c b/tools/quake3/common/vfs.c
index 8f5e57bf..0bd6ed1e 100644
--- a/tools/quake3/common/vfs.c
+++ b/tools/quake3/common/vfs.c
@@ -304,6 +304,56 @@ int vfsGetFileCount( const char *filename ){
 	return count;
 }
 
+static qboolean isSymlink(const unz_file_info64 *fileInfo) {
+	// see https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/uapi/linux/stat.h
+	// redefine so it works outside of Unices
+	const unsigned long Q3MAP_S_IFMT = 00170000;
+	const unsigned long Q3MAP_S_IFLNK = 0120000;
+	// see https://trac.edgewall.org/attachment/ticket/8919/ZipDownload.patch
+	const unsigned long PKZIP_EXTERNAL_ATTR_FILE_TYPE_SHIFT = 16;
+
+	unsigned long attr = fileInfo->external_fa >> PKZIP_EXTERNAL_ATTR_FILE_TYPE_SHIFT;
+	return (attr & Q3MAP_S_IFMT) == Q3MAP_S_IFLNK;
+}
+
+// The zip format has a maximum filename size of 64K
+static const int MAX_FILENAME_BUF = 65537;
+
+/* The symlink implementation is ported from Dæmon engine implementation by slipher which was a complete rewrite of one illwieckz did on Dæmon by taking inspiration from Darkplaces engine.
+
+See:
+
+- https://github.com/DaemonEngine/Daemon/blob/master/src/common/FileSystem.cpp
+- https://gitlab.com/xonotic/darkplaces/-/blob/div0-stable/fs.c
+
+Some words by slipher:
+
+> Symlinks are a bad feature which you should not use. Therefore, the implementation is as
+> slow as possible with a full iteration of the archive performed for each symlink.
+
+> The symlink path `relative` must be relative to the symlink's location.
+> Only supports paths consisting of "../" 0 or more times, followed by non-magical path components.
+*/
+void resolveSymlinkPath( const char* base, const char* relative, char* resolved ){
+
+	base = g_path_get_dirname( base );
+
+	while( g_str_has_prefix( relative, "../" ) )
+	{
+		if ( base[0] == '\0' )
+		{
+			Sys_FPrintf( SYS_WRN, "Error while reading symbolic link: \"%s\": no such directory\n", base );
+			resolved[0] = '\0';
+			return;
+		}
+
+		base = g_path_get_dirname( base );
+		relative += 3;
+	}
+
+	snprintf( resolved, MAX_FILENAME_BUF, "%s/%s", base, relative);
+}
+
 // NOTE: when loading a file, you have to allocate one extra byte and set it to \0
 int vfsLoadFile( const char *filename, void **bufferptr, int index ){
 	int i, count = 0;
@@ -388,6 +438,11 @@ int vfsLoadFile( const char *filename, void **bufferptr, int index ){
 		}
 	}
 
+	// Do not resolve more than 5 recursive symbolic links to
+	// prevent circular symbolic links.
+	int max_symlink_depth = 5;
+
+	openSymlinkTarget:
 	for ( lst = g_pakFiles; lst != NULL; lst = g_slist_next( lst ) )
 	{
 		VFS_PAKFILE* file = (VFS_PAKFILE*)lst->data;
@@ -405,12 +460,45 @@ int vfsLoadFile( const char *filename, void **bufferptr, int index ){
 				return -1;
 			}
 
+			unz_file_info64 fileInfo;
+			if ( unzGetCurrentFileInfo64( file->zipfile, &fileInfo, filename, sizeof(filename), NULL, 0, NULL, 0 ) != UNZ_OK ) {
+				return -1;
+			}
+
 			*bufferptr = safe_malloc( file->size + 1 );
 			// we need to end the buffer with a 0
 			( (char*) ( *bufferptr ) )[file->size] = 0;
 
 			i = unzReadCurrentFile( file->zipfile, *bufferptr, file->size );
 			unzCloseCurrentFile( file->zipfile );
+
+			if ( isSymlink( &fileInfo ) ) {
+				Sys_FPrintf( SYS_VRB, "Found symbolic link: \"%s\"\n", filename );
+
+				if ( max_symlink_depth == 0 ) {
+					Sys_FPrintf( SYS_WRN, "Maximum symbolic link depth reached\n" );
+					g_free( lower );
+					return -1;
+				}
+
+				max_symlink_depth--;
+
+				const char* relative = (const char*) *bufferptr;
+				char resolved[MAX_FILENAME_BUF];
+
+				resolveSymlinkPath( file->name, relative, resolved );
+
+				Sys_FPrintf( SYS_VRB, "Resolved symbolic link: \"%s\"\n", resolved );
+
+				g_free( lower );
+				strncpy( fixed, resolved, sizeof( fixed ) );
+				vfsFixDOSName( fixed );
+				lower = g_ascii_strdown( fixed, -1 );
+
+				// slow as possible full iteration of the archive
+				goto openSymlinkTarget;
+			}
+
 			if ( i < 0 ) {
 				g_free( lower );
 				return -1;
@@ -423,6 +511,7 @@ int vfsLoadFile( const char *filename, void **bufferptr, int index ){
 
 		count++;
 	}
+
 	g_free( lower );
 	return -1;
 }
-- 
2.39.2