exec: do not call request_module() twice from search_binary_handler()

BugLink: http://bugs.launchpad.net/bugs/881420

commit 912193521b719fbfc2f16776febf5232fe8ba261 upstream.

Currently, search_binary_handler() tries to load binary loader module
using request_module() if a loader for the requested program is not yet
loaded.  But second attempt of request_module() does not affect the result
of search_binary_handler().

If request_module() triggered recursion, calling request_module() twice
causes 2 to the power of MAX_KMOD_CONCURRENT (= 50) repetitions.  It is
not an infinite loop but is sufficient for users to consider as a hang up.

Therefore, this patch changes not to call request_module() twice, making 1
to the power of MAX_KMOD_CONCURRENT repetitions in case of recursion.

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reported-by: Richard Weinberger <richard@nod.at>
Tested-by: Richard Weinberger <richard@nod.at>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Maxim Uvarov <muvarov@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/fs/exec.c b/fs/exec.c
index c122d78f11b..d3baab6b8bc 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1415,6 +1415,8 @@ int search_binary_handler(struct linux_binprm *bprm,struct pt_regs *regs)
                             printable(bprm->buf[2]) &&
                             printable(bprm->buf[3]))
                                 break; /* -ENOEXEC */
+                        if (try)
+                                break; /* -ENOEXEC */
                         request_module("binfmt-%04x", *(unsigned short *)(&bprm->buf[2]));
 #endif
                 }