exec: remove legacy custom binfmt modules autoloading

Problem: The search binary handler logic contains legacy code
to handle automatically loading kernel modules of unsupported
binary formats.
This logic is a leftover from a.out-to-ELF transition.
After removal of a.out support, this code has no use anymore.

Solution: Clean up this code from the search binary handler,
also remove the line initialising retval to -ENOENT and instead
just return -ENOEXEC if the flow has reached the end of the func.

Note: Anyone who might find future uses for this legacy code
would be better off using binfmt_misc to trigger whatever
module loading they might need - would be more flexible that way.

Suggested-by: Alexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Nir Lichtman <nir@lichtman.org>
Link: https://lore.kernel.org/r/20241116231323.GA225987@lichtman.org
Signed-off-by: Kees Cook <kees@kernel.org>

diff --git a/fs/exec.c b/fs/exec.c
index 4057b8c3e23391ead12a025b566c867d9a085d4c..e0435b31a811af1bca5f18dac5382a4f1e271930 100644 (file)
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1723,13 +1723,11 @@ int remove_arg_zero(struct linux_binprm *bprm)
 }
 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
  */
 static int search_binary_handler(struct linux_binprm *bprm)
 {
-       bool need_retry = IS_ENABLED(CONFIG_MODULES);
        struct linux_binfmt *fmt;
        int retval;
 
@@ -1741,8 +1739,6 @@ static int search_binary_handler(struct linux_binprm *bprm)
        if (retval)
                return retval;
 
-       retval = -ENOENT;
- retry:
        read_lock(&binfmt_lock);
        list_for_each_entry(fmt, &formats, lh) {
                if (!try_module_get(fmt->module))
@@ -1760,17 +1756,7 @@ static int search_binary_handler(struct linux_binprm *bprm)
        }
        read_unlock(&binfmt_lock);
 
-       if (need_retry) {
-               if (printable(bprm->buf[0]) && printable(bprm->buf[1]) &&
-                   printable(bprm->buf[2]) && printable(bprm->buf[3]))
-                       return retval;
-               if (request_module("binfmt-%04x", *(ushort *)(bprm->buf + 2)) < 0)
-                       return retval;
-               need_retry = false;
-               goto retry;
-       }
-
-       return retval;
+       return -ENOEXEC;
 }
 
 /* binfmt handlers will call back into begin_new_exec() on success. */