exec: use -ELOOP for max recursion depth

To avoid an explosion of request_module calls on a chain of abusive
scripts, fail maximum recursion with -ELOOP instead of -ENOEXEC. As soon
as maximum recursion depth is hit, the error will fail all the way back
up the chain, aborting immediately.

This also has the side-effect of stopping the user's shell from attempting
to reexecute the top-level file as a shell script. As seen in the
dash source:

        if (cmd != path_bshell && errno == ENOEXEC) {
                *argv-- = cmd;
                *argv = cmd = path_bshell;
                goto repeat;
        }

The above logic was designed for running scripts automatically that lacked
the "#!" header, not to re-try failed recursion. On a legitimate -ENOEXEC,
things continue to behave as the shell expects.

Additionally, when tracking recursion, the binfmt handlers should not be
involved. The recursion being tracked is the depth of calls through
search_binary_handler(), so that function should be exclusively responsible
for tracking the depth.

Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: halfdog <me@halfdog.net>
Cc: P J P <ppandit@redhat.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 0 insertions, 6 deletions

diff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c
index b0b70fbea06c..9be335fb8a7c 100644
--- a/fs/binfmt_misc.c
+++ b/fs/binfmt_misc.c
@@ -117,10 +117,6 @@ static int load_misc_binary(struct linux_binprm *bprm)
         if (!enabled)
                 goto _ret;
 
-        retval = -ENOEXEC;
-        if (bprm->recursion_depth > BINPRM_MAX_RECURSION)
-                goto _ret;
-
         /* to keep locking time low, we copy the interpreter string */
         read_lock(&entries_lock);
         fmt = check_file(bprm);
@@ -197,8 +193,6 @@ static int load_misc_binary(struct linux_binprm *bprm)
         if (retval < 0)
                 goto _error;
 
-        bprm->recursion_depth++;
-
         retval = search_binary_handler(bprm);
         if (retval < 0)
                 goto _error;