[PATCH 3.16 113/346] module: Invalidate signatures on force-loaded modules

[Ben Hutchings]

3.16.39-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Ben Hutchings <ben@xxxxxxxxxxxxxxx>

commit bca014caaa6130e57f69b5bf527967aa8ee70fdd upstream.

Signing a module should only make it trusted by the specific kernel it
was built for, not anything else.  Loading a signed module meant for a
kernel with a different ABI could have interesting effects.
Therefore, treat all signatures as invalid when a module is
force-loaded.

Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
Signed-off-by: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
---
 kernel/module.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2435,13 +2435,18 @@ static inline void kmemleak_load_module(
 #endif
 
 #ifdef CONFIG_MODULE_SIG
-static int module_sig_check(struct load_info *info)
+static int module_sig_check(struct load_info *info, int flags)
 {
 	int err = -ENOKEY;
 	const unsigned long markerlen = sizeof(MODULE_SIG_STRING) - 1;
 	const void *mod = info->hdr;
 
-	if (info->len > markerlen &&
+	/*
+	 * Require flags == 0, as a module with version information
+	 * removed is no longer the module that was signed
+	 */
+	if (flags == 0 &&
+	    info->len > markerlen &&
 	    memcmp(mod + info->len - markerlen, MODULE_SIG_STRING, markerlen) == 0) {
 		/* We truncate the module to discard the signature */
 		info->len -= markerlen;
@@ -2463,7 +2468,7 @@ static int module_sig_check(struct load_
 	return err;
 }
 #else /* !CONFIG_MODULE_SIG */
-static int module_sig_check(struct load_info *info)
+static int module_sig_check(struct load_info *info, int flags)
 {
 	return 0;
 }
@@ -3200,7 +3205,7 @@ static int load_module(struct load_info
 	long err;
 	char *after_dashes;
 
-	err = module_sig_check(info);
+	err = module_sig_check(info, flags);
 	if (err)
 		goto free_copy;