[PATCH 4.4 118/143] Revert "exec: load_script: dont blindly truncate shebang string"

[Greg Kroah-Hartman]

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>

commit cb5b020a8d38f77209d0472a0fea755299a8ec78 upstream.

This reverts commit 8099b047ecc431518b9bb6bdbba3549bbecdc343.

It turns out that people do actually depend on the shebang string being
truncated, and on the fact that an interpreter (like perl) will often
just re-interpret it entirely to get the full argument list.

Reported-by: Samuel Dionne-Riel <samuel@xxxxxxxxxxxxxxx>
Acked-by: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 fs/binfmt_script.c |   10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

--- a/fs/binfmt_script.c
+++ b/fs/binfmt_script.c
@@ -43,14 +43,10 @@ static int load_script(struct linux_binp
 	fput(bprm->file);
 	bprm->file = NULL;
 
-	for (cp = bprm->buf+2;; cp++) {
-		if (cp >= bprm->buf + BINPRM_BUF_SIZE)
-			return -ENOEXEC;
-		if (!*cp || (*cp == '\n'))
-			break;
-	}
+	bprm->buf[BINPRM_BUF_SIZE - 1] = '\0';
+	if ((cp = strchr(bprm->buf, '\n')) == NULL)
+		cp = bprm->buf+BINPRM_BUF_SIZE-1;
 	*cp = '\0';
-
 	while (cp > bprm->buf) {
 		cp--;
 		if ((*cp == ' ') || (*cp == '\t'))