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SubjectRe: [PATCH 0/2] module: some refactoring in module_sig_check()
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On Tue, 2020-10-13 at 23:32 +0300, Sergey Shtylyov wrote:
> Here are 2 patches against the 'modules-next' branch of Jessica Yu's 'linux.git' repo.
> I'm doing some little refactoring in module_sig_check()...
>
> [1/2] module: merge repetitive strings in module_sig_check()
> [2/2] module: unindent comments in module_sig_check()

I think this code is rather cryptic and could be made clearer.

How about:
---
kernel/module.c | 51 ++++++++++++++++++++++++++-------------------------
1 file changed, 26 insertions(+), 25 deletions(-)

diff --git a/kernel/module.c b/kernel/module.c
index c075a18103fb..98b3af96a5bd 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2884,46 +2884,47 @@ static int module_sig_check(struct load_info *info, int flags)
* 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) {
+ if (flags == 0 && info->len > markerlen &&
+ !memcmp(mod + info->len - markerlen, MODULE_SIG_STRING, markerlen)) {
/* We truncate the module to discard the signature */
info->len -= markerlen;
err = mod_verify_sig(mod, info);
+ if (!err) {
+ info->sig_ok = true;
+ return 0;
+ }
}

+ /*
+ * We don't permit modules to be loaded into trusted kernels
+ * without a valid signature on them, but if we're not enforcing,
+ * some errors are non-fatal.
+ */
switch (err) {
- case 0:
- info->sig_ok = true;
- return 0;
-
- /* We don't permit modules to be loaded into trusted kernels
- * without a valid signature on them, but if we're not
- * enforcing, certain errors are non-fatal.
- */
case -ENODATA:
- reason = "Loading of unsigned module";
- goto decide;
+ reason = "unsigned module";
+ break;
case -ENOPKG:
- reason = "Loading of module with unsupported crypto";
- goto decide;
+ reason = "module with unsupported crypto";
+ break;
case -ENOKEY:
- reason = "Loading of module with unavailable key";
- decide:
- if (is_module_sig_enforced()) {
- pr_notice("%s: %s is rejected\n", info->name, reason);
- return -EKEYREJECTED;
- }
-
- return security_locked_down(LOCKDOWN_MODULE_SIGNATURE);
-
+ reason = "module with unavailable key";
+ break;
+ default:
/* All other errors are fatal, including nomem, unparseable
* signatures and signature check failures - even if signatures
* aren't required.
*/
- default:
return err;
}
+
+ if (is_module_sig_enforced()) {
+ pr_notice("%s: loading of %s is rejected\n",
+ info->name, reason);
+ return -EKEYREJECTED;
+ }
+
+ return security_locked_down(LOCKDOWN_MODULE_SIGNATURE);
}
#else /* !CONFIG_MODULE_SIG */
static int module_sig_check(struct load_info *info, int flags)

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