exec: kill ->load_binary != NULL check in search_binary_handler()

search_binary_handler() checks ->load_binary != NULL for no reason, this
method should be always defined.  Turn this check into WARN_ON() and move
it into __register_binfmt().

Also, kill the function pointer.  The current code looks confusing, as if
->load_binary can go away after read_unlock(&binfmt_lock).  But we rely on
module_get(fmt->module), this fmt can't be changed or unregistered,
otherwise this code is buggy anyway.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Evgeniy Polyakov <zbr@ioremap.net>
Cc: Zach Levis <zml@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 4 deletions

diff --git a/fs/exec.c b/fs/exec.c
index a4cfd1d725e0..7b92fbfa63aa 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -74,6 +74,8 @@ static DEFINE_RWLOCK(binfmt_lock);
 void __register_binfmt(struct linux_binfmt * fmt, int insert)
 {
         BUG_ON(!fmt);
+        if (WARN_ON(!fmt->load_binary))
+                return;
         write_lock(&binfmt_lock);
         insert ? list_add(&fmt->lh, &formats) :
                  list_add_tail(&fmt->lh, &formats);
@@ -1389,14 +1391,11 @@ int search_binary_handler(struct linux_binprm *bprm)
         for (try=0; try<2; try++) {
                 read_lock(&binfmt_lock);
                 list_for_each_entry(fmt, &formats, lh) {
-                        int (*fn)(struct linux_binprm *) = fmt->load_binary;
-                        if (!fn)
-                                continue;
                         if (!try_module_get(fmt->module))
                                 continue;
                         read_unlock(&binfmt_lock);
                         bprm->recursion_depth++;
-                        retval = fn(bprm);
+                        retval = fmt->load_binary(bprm);
                         bprm->recursion_depth--;
                         if (retval >= 0) {
                                 put_binfmt(fmt);