1 files changed, 46 insertions, 11 deletions

diff --git a/fs/binfmt_script.c b/fs/binfmt_script.c
index d0078cbb718b..e996174cbfc0 100644
--- a/fs/binfmt_script.c
+++ b/fs/binfmt_script.c
@@ -14,13 +14,30 @@
 #include <linux/err.h>
 #include <linux/fs.h>
 
+static inline bool spacetab(char c) { return c == ' ' || c == '\t'; }
+static inline char *next_non_spacetab(char *first, const char *last)
+{
+	for (; first <= last; first++)
+		if (!spacetab(*first))
+			return first;
+	return NULL;
+}
+static inline char *next_terminator(char *first, const char *last)
+{
+	for (; first <= last; first++)
+		if (spacetab(*first) || !*first)
+			return first;
+	return NULL;
+}
+
 static int load_script(struct linux_binprm *bprm)
 {
 	const char *i_arg, *i_name;
-	char *cp;
+	char *cp, *buf_end;
 	struct file *file;
 	int retval;
 
+	/* Not ours to exec if we don't start with "#!". */
 	if ((bprm->buf[0] != '#') || (bprm->buf[1] != '!'))
 		return -ENOEXEC;
 
@@ -33,23 +50,41 @@ static int load_script(struct linux_binprm *bprm)
 	if (bprm->interp_flags & BINPRM_FLAGS_PATH_INACCESSIBLE)
 		return -ENOENT;
 
-	/*
-	 * This section does the #! interpretation.
-	 * Sorta complicated, but hopefully it will work.  -TYT
-	 */
-
+	/* Release since we are not mapping a binary into memory. */
 	allow_write_access(bprm->file);
 	fput(bprm->file);
 	bprm->file = NULL;
 
-	for (cp = bprm->buf+2;; cp++) {
-		if (cp >= bprm->buf + BINPRM_BUF_SIZE)
+	/*
+	 * This section handles parsing the #! line into separate
+	 * interpreter path and argument strings. We must be careful
+	 * because bprm->buf is not yet guaranteed to be NUL-terminated
+	 * (though the buffer will have trailing NUL padding when the
+	 * file size was smaller than the buffer size).
+	 *
+	 * We do not want to exec a truncated interpreter path, so either
+	 * we find a newline (which indicates nothing is truncated), or
+	 * we find a space/tab/NUL after the interpreter path (which
+	 * itself may be preceded by spaces/tabs). Truncating the
+	 * arguments is fine: the interpreter can re-read the script to
+	 * parse them on its own.
+	 */
+	buf_end = bprm->buf + sizeof(bprm->buf) - 1;
+	cp = strnchr(bprm->buf, sizeof(bprm->buf), '\n');
+	if (!cp) {
+		cp = next_non_spacetab(bprm->buf + 2, buf_end);
+		if (!cp)
+			return -ENOEXEC; /* Entire buf is spaces/tabs */
+		/*
+		 * If there is no later space/tab/NUL we must assume the
+		 * interpreter path is truncated.
+		 */
+		if (!next_terminator(cp, buf_end))
 			return -ENOEXEC;
-		if (!*cp || (*cp == '\n'))
-			break;
+		cp = buf_end;
 	}
+	/* NUL-terminate the buffer and any trailing spaces/tabs. */
 	*cp = '\0';
-
 	while (cp > bprm->buf) {
 		cp--;
 		if ((*cp == ' ') || (*cp == '\t'))