Fix bug #66171: better handling of symlinks

2 files changed, 22 insertions, 17 deletions

diff --git a/NEWS b/NEWS
index 1d8fe401b0..66f0d05645 100644
--- a/NEWS
+++ b/NEWS
@@ -8,6 +8,8 @@ PHP                                                                        NEWS
     UNIX sockets). (Mike)
   . Fixed bug #64604 (parse_url is inconsistent with specified port). 
     (Ingo Walz)
+  . Fixed bug #66171 (Symlinks and session handler allow open_basedir bypass).
+    (Jann Horn, Stas)
   . Fixed bug #66182 (exit in stream filter produces segfault). (Mike)
   . Fixed bug #66736 (fpassthru broken). (Mike)
   . Fixed bug #67024 (getimagesize should recognize BMP files with negative 
diff --git a/ext/session/mod_files.c b/ext/session/mod_files.c
index 86a2235845..8f57ca5af9 100644
--- a/ext/session/mod_files.c
+++ b/ext/session/mod_files.c
@@ -146,6 +146,7 @@ static void ps_files_close(ps_files *data)
 static void ps_files_open(ps_files *data, const char *key TSRMLS_DC)
 {
 	char buf[MAXPATHLEN];
+    struct stat sbuf;
 
 	if (data->fd < 0 || !data->lastkey || strcmp(key, data->lastkey)) {
 		if (data->lastkey) {
@@ -165,26 +166,28 @@ static void ps_files_open(ps_files *data, const char *key TSRMLS_DC)
 		}
 
 		data->lastkey = estrdup(key);
-
-		data->fd = VCWD_OPEN_MODE(buf, O_CREAT | O_RDWR | O_BINARY, data->filemode);
+                       
+        /* O_NOFOLLOW to prevent us from following evil symlinks */
+#ifdef O_NOFOLLOW
+        data->fd = VCWD_OPEN_MODE(buf, O_CREAT | O_RDWR | O_BINARY | O_NOFOLLOW, data->filemode);
+#else
+        /* Check to make sure that the opened file is not outside of allowable dirs. 
+           This is not 100% safe but it's hard to do something better without O_NOFOLLOW */
+        if(PG(open_basedir) && lstat(buf, &sbuf) == 0 && S_ISLNK(sbuf.st_mode) && php_check_open_basedir(buf TSRMLS_CC)) {
+            return;
+        }
+        data->fd = VCWD_OPEN_MODE(buf, O_CREAT | O_RDWR | O_BINARY, data->filemode);
+#endif
 
 		if (data->fd != -1) {
 #ifndef PHP_WIN32
-			/* check to make sure that the opened file is not a symlink, linking to data outside of allowable dirs */
-			if (PG(open_basedir)) {
-				struct stat sbuf;
-
-				if (fstat(data->fd, &sbuf)) {
-					close(data->fd);
-					data->fd = -1;
-					return;
-				}
-				if (S_ISLNK(sbuf.st_mode) && php_check_open_basedir(buf TSRMLS_CC)) {
-					close(data->fd);
-					data->fd = -1;
-					return;
-				}
-			}
+            /* check that this session file was created by us or root – we
+               don't want to end up accepting the sessions of another webapp */
+            if (fstat(data->fd, &sbuf) || (sbuf.st_uid != 0 && sbuf.st_uid != getuid() && sbuf.st_uid != geteuid())) {
+				close(data->fd);
+				data->fd = -1;
+				return;
+            }
 #endif
 			flock(data->fd, LOCK_EX);