exec: cleanup the CONFIG_MODULES logic

search_binary_handler() uses "for (try=0; try<2; try++)" to avoid "goto"
but the code looks too complicated and horrible imho.  We still need to
check "try == 0" before request_module() and add the additional "break"
for !CONFIG_MODULES case.

Kill this loop and use a simple "bool need_retry" + "goto retry".  The
code looks much simpler and we do not even need ifdef's, gcc can optimize
out the "if (need_retry)" block if !IS_ENABLED().

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, 31 insertions, 37 deletions

diff --git a/fs/exec.c b/fs/exec.c
index 7b92fbfa63aa..ba357e6aea98 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1367,13 +1367,15 @@ out:
 }
 EXPORT_SYMBOL(remove_arg_zero);
 
+#define printable(c) (((c)=='\t') || ((c)=='\n') || (0x20<=(c) && (c)<=0x7e))
 /*
  * cycle the list of binary formats handler, until one recognizes the image
  */
 int search_binary_handler(struct linux_binprm *bprm)
 {
-        int try, retval;
+        bool need_retry = IS_ENABLED(CONFIG_MODULES);
         struct linux_binfmt *fmt;
+        int retval;
 
         /* This allows 4 levels of binfmt rewrites before failing hard. */
         if (bprm->recursion_depth > 5)
@@ -1388,47 +1390,39 @@ int search_binary_handler(struct linux_binprm *bprm)
                 return retval;
 
         retval = -ENOENT;
-        for (try=0; try<2; try++) {
-                read_lock(&binfmt_lock);
-                list_for_each_entry(fmt, &formats, lh) {
-                        if (!try_module_get(fmt->module))
-                                continue;
-                        read_unlock(&binfmt_lock);
-                        bprm->recursion_depth++;
-                        retval = fmt->load_binary(bprm);
-                        bprm->recursion_depth--;
-                        if (retval >= 0) {
-                                put_binfmt(fmt);
-                                return retval;
-                        }
-                        read_lock(&binfmt_lock);
+ retry:
+        read_lock(&binfmt_lock);
+        list_for_each_entry(fmt, &formats, lh) {
+                if (!try_module_get(fmt->module))
+                        continue;
+                read_unlock(&binfmt_lock);
+                bprm->recursion_depth++;
+                retval = fmt->load_binary(bprm);
+                bprm->recursion_depth--;
+                if (retval >= 0) {
                         put_binfmt(fmt);
-                        if (retval != -ENOEXEC || bprm->mm == NULL)
-                                break;
-                        if (!bprm->file) {
-                                read_unlock(&binfmt_lock);
-                                return retval;
-                        }
+                        return retval;
                 }
-                read_unlock(&binfmt_lock);
-#ifdef CONFIG_MODULES
-                if (retval != -ENOEXEC || bprm->mm == NULL) {
+                read_lock(&binfmt_lock);
+                put_binfmt(fmt);
+                if (retval != -ENOEXEC || bprm->mm == NULL)
                         break;
-                } else {
-#define printable(c) (((c)=='\t') || ((c)=='\n') || (0x20<=(c) && (c)<=0x7e))
-                        if (printable(bprm->buf[0]) &&
-                            printable(bprm->buf[1]) &&
-                            printable(bprm->buf[2]) &&
-                            printable(bprm->buf[3]))
-                                break; /* -ENOEXEC */
-                        if (try)
-                                break; /* -ENOEXEC */
-                        request_module("binfmt-%04x", *(unsigned short *)(&bprm->buf[2]));
+                if (!bprm->file) {
+                        read_unlock(&binfmt_lock);
+                        return retval;
                 }
-#else
-                break;
-#endif
         }
+        read_unlock(&binfmt_lock);
+
+        if (need_retry && retval == -ENOEXEC && bprm->mm) {
+                if (printable(bprm->buf[0]) && printable(bprm->buf[1]) &&
+                    printable(bprm->buf[2]) && printable(bprm->buf[3]))
+                        return retval;
+                request_module("binfmt-%04x", *(ushort *)(bprm->buf + 2));
+                need_retry = false;
+                goto retry;
+        }
+
         return retval;
 }
 EXPORT_SYMBOL(search_binary_handler);