Re: [PATCH 04/30] Enforce module signatures if the kernel is locked down

[Jiri Bohac]

On Thu, Feb 22, 2018 at 01:07:57PM +, David Howells wrote:
> I'm considering folding the attached changes into this patch.
> 
> It adjusts the errors generated:
> 
>  (1) If there's no signature (ENODATA) or we can't check it (ENOPKG, ENOKEY),
>  then:
> 
>  (a) If signatures are enforced then EKEYREJECTED is returned.
> 
>  (b) If IMA will have validated the image, return 0 (okay).
> 
>  (c) If there's no signature or we can't check it, but the kernel is
>locked down then EPERM is returned (this is then consistent with
>other lockdown cases).
> 
>  (2) If the signature is unparseable (EBADMSG, EINVAL), the signature fails
>  the check (EKEYREJECTED) or a system error occurs (eg. ENOMEM), we return
>  the error we got.
> 
> Note that the X.509 code doesn't check for key expiry as the RTC might not be
> valid or might not have been transferred to the kernel's clock yet.

Looks good. 

Reviewed-by: Jiri Bohac 

-- 
Jiri Bohac 
SUSE Labs, Prague, Czechia

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Re: [PATCH 04/30] Enforce module signatures if the kernel is locked down

[David Howells]

I'm considering folding the attached changes into this patch.

It adjusts the errors generated:

 (1) If there's no signature (ENODATA) or we can't check it (ENOPKG, ENOKEY),
 then:

 (a) If signatures are enforced then EKEYREJECTED is returned.

 (b) If IMA will have validated the image, return 0 (okay).

 (c) If there's no signature or we can't check it, but the kernel is
 locked down then EPERM is returned (this is then consistent with
 other lockdown cases).

 (2) If the signature is unparseable (EBADMSG, EINVAL), the signature fails
 the check (EKEYREJECTED) or a system error occurs (eg. ENOMEM), we return
 the error we got.

Note that the X.509 code doesn't check for key expiry as the RTC might not be
valid or might not have been transferred to the kernel's clock yet.

David
---
diff --git a/kernel/module.c b/kernel/module.c
index 1eb06a0ccbfb..62419cf48ef6 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2769,8 +2769,9 @@ static inline void kmemleak_load_module(const struct 
module *mod,
 static int module_sig_check(struct load_info *info, int flags,
bool can_do_ima_check)
 {
-   int err = -ENOKEY;
+   int err = -ENODATA;
const unsigned long markerlen = sizeof(MODULE_SIG_STRING) - 1;
+   const char *reason;
const void *mod = info->hdr;
 
/*
@@ -2785,18 +2786,42 @@ static int module_sig_check(struct load_info *info, int 
flags,
err = mod_verify_sig(mod, >len);
}
 
-   if (!err) {
+   switch (err) {
+   case 0:
info->sig_ok = true;
return 0;
-   }
 
-   /* Not having a signature is only an error if we're strict. */
-   if (err == -ENOKEY && !sig_enforce &&
-   (!can_do_ima_check || !is_ima_appraise_enabled()) &&
-   !kernel_is_locked_down("Loading of unsigned modules"))
-   err = 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;
+   case -ENOPKG:
+   reason = "Loading of module with unsupported crypto";
+   goto decide;
+   case -ENOKEY:
+   reason = "Loading of module with unavailable key";
+   decide:
+   if (sig_enforce) {
+   pr_notice("%s is rejected\n", reason);
+   return -EKEYREJECTED;
+   }
 
-   return err;
+   if (can_do_ima_check && is_ima_appraise_enabled())
+   return 0;
+   if (kernel_is_locked_down(reason))
+   return -EPERM;
+   return 0;
+
+   /* All other errors are fatal, including nomem, unparseable
+* signatures and signature check failures - even if signatures
+* aren't required.
+*/
+   default:
+   return err;
+   }
 }
 #else /* !CONFIG_MODULE_SIG */
 static int module_sig_check(struct load_info *info, int flags,
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[PATCH 04/30] Enforce module signatures if the kernel is locked down

[David Howells]

If the kernel is locked down, require that all modules have valid
signatures that we can verify or that IMA can validate the file.

Signed-off-by: David Howells 
Reviewed-by: "Lee, Chun-Yi" 
Reviewed-by: James Morris 
---

 kernel/module.c |   19 ---
 1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/kernel/module.c b/kernel/module.c
index de66ec825992..0ce29c8aa75a 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -64,6 +64,7 @@
 #include 
 #include 
 #include 
+#include 
 #include 
 #include "module-internal.h"
 
@@ -2757,7 +2758,8 @@ static inline void kmemleak_load_module(const struct 
module *mod,
 #endif
 
 #ifdef CONFIG_MODULE_SIG
-static int module_sig_check(struct load_info *info, int flags)
+static int module_sig_check(struct load_info *info, int flags,
+   bool can_do_ima_check)
 {
int err = -ENOKEY;
const unsigned long markerlen = sizeof(MODULE_SIG_STRING) - 1;
@@ -2781,13 +2783,16 @@ static int module_sig_check(struct load_info *info, int 
flags)
}
 
/* Not having a signature is only an error if we're strict. */
-   if (err == -ENOKEY && !sig_enforce)
+   if (err == -ENOKEY && !sig_enforce &&
+   (!can_do_ima_check || !is_ima_appraise_enabled()) &&
+   !kernel_is_locked_down("Loading of unsigned modules"))
err = 0;
 
return err;
 }
 #else /* !CONFIG_MODULE_SIG */
-static int module_sig_check(struct load_info *info, int flags)
+static int module_sig_check(struct load_info *info, int flags,
+   bool can_do_ima_check)
 {
return 0;
 }
@@ -3630,13 +3635,13 @@ static int unknown_module_param_cb(char *param, char 
*val, const char *modname,
 /* Allocate and load the module: note that size of section 0 is always
zero, and we rely on this for optional sections. */
 static int load_module(struct load_info *info, const char __user *uargs,
-  int flags)
+  int flags, bool can_do_ima_check)
 {
struct module *mod;
long err;
char *after_dashes;
 
-   err = module_sig_check(info, flags);
+   err = module_sig_check(info, flags, can_do_ima_check);
if (err)
goto free_copy;
 
@@ -3830,7 +3835,7 @@ SYSCALL_DEFINE3(init_module, void __user *, umod,
if (err)
return err;
 
-   return load_module(, uargs, 0);
+   return load_module(, uargs, 0, false);
 }
 
 SYSCALL_DEFINE3(finit_module, int, fd, const char __user *, uargs, int, flags)
@@ -3857,7 +3862,7 @@ SYSCALL_DEFINE3(finit_module, int, fd, const char __user 
*, uargs, int, flags)
info.hdr = hdr;
info.len = size;
 
-   return load_module(, uargs, flags);
+   return load_module(, uargs, flags, true);
 }
 
 static inline int within(unsigned long addr, void *start, unsigned long size)

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