Commit 8c0637e950d6 ("keys: Make the KEY_NEED_* perms an enum rather than
a mask") changed the type of the key_permission callback functions, but
didn't change the type of the hook, which trips indirect call checking with
Control-Flow Integrity (CFI). This change fixes the issue by changing the
hook type to match the functions.
Fixes: 8c0637e950d6 ("keys: Make the KEY_NEED_* perms an enum rather than a mask")
Signed-off-by: Sami Tolvanen <[email protected]>
---
include/linux/lsm_hook_defs.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
index 6791813cd439..24f6683f1cfc 100644
--- a/include/linux/lsm_hook_defs.h
+++ b/include/linux/lsm_hook_defs.h
@@ -360,7 +360,7 @@ LSM_HOOK(int, 0, key_alloc, struct key *key, const struct cred *cred,
unsigned long flags)
LSM_HOOK(void, LSM_RET_VOID, key_free, struct key *key)
LSM_HOOK(int, 0, key_permission, key_ref_t key_ref, const struct cred *cred,
- unsigned perm)
+ enum key_need_perm need_perm)
LSM_HOOK(int, 0, key_getsecurity, struct key *key, char **_buffer)
#endif /* CONFIG_KEYS */
base-commit: b3a9e3b9622ae10064826dccb4f7a52bd88c7407
--
2.27.0.290.gba653c62da-goog
On Mon, Jun 15, 2020 at 11:12:32AM -0700, Sami Tolvanen wrote:
> Commit 8c0637e950d6 ("keys: Make the KEY_NEED_* perms an enum rather than
> a mask") changed the type of the key_permission callback functions, but
> didn't change the type of the hook, which trips indirect call checking with
> Control-Flow Integrity (CFI). This change fixes the issue by changing the
> hook type to match the functions.
>
> Fixes: 8c0637e950d6 ("keys: Make the KEY_NEED_* perms an enum rather than a mask")
> Signed-off-by: Sami Tolvanen <[email protected]>
Thanks for fixing this!
Acked-by: Kees Cook <[email protected]>
I wonder if there is any compiler option we can turn on to catch the
implicit enum/int casting that would help for these kinds of things
without absolutely exploding the build warnings.
I see -Wenum-conversion, but that seems to be between enums, not between
int.
I see this, but it's external:
https://noamlewis.wordpress.com/2017/10/05/type-safe-enums-in-c-using-a-clang-plugin/
-Kees
> ---
> include/linux/lsm_hook_defs.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
> index 6791813cd439..24f6683f1cfc 100644
> --- a/include/linux/lsm_hook_defs.h
> +++ b/include/linux/lsm_hook_defs.h
> @@ -360,7 +360,7 @@ LSM_HOOK(int, 0, key_alloc, struct key *key, const struct cred *cred,
> unsigned long flags)
> LSM_HOOK(void, LSM_RET_VOID, key_free, struct key *key)
> LSM_HOOK(int, 0, key_permission, key_ref_t key_ref, const struct cred *cred,
> - unsigned perm)
> + enum key_need_perm need_perm)
> LSM_HOOK(int, 0, key_getsecurity, struct key *key, char **_buffer)
> #endif /* CONFIG_KEYS */
>
>
> base-commit: b3a9e3b9622ae10064826dccb4f7a52bd88c7407
> --
> 2.27.0.290.gba653c62da-goog
>
--
Kees Cook
On Mon, Jun 15, 2020 at 11:21 AM Kees Cook <[email protected]> wrote:
>
> On Mon, Jun 15, 2020 at 11:12:32AM -0700, Sami Tolvanen wrote:
> > Commit 8c0637e950d6 ("keys: Make the KEY_NEED_* perms an enum rather than
> > a mask") changed the type of the key_permission callback functions, but
> > didn't change the type of the hook, which trips indirect call checking with
> > Control-Flow Integrity (CFI). This change fixes the issue by changing the
> > hook type to match the functions.
> >
> > Fixes: 8c0637e950d6 ("keys: Make the KEY_NEED_* perms an enum rather than a mask")
> > Signed-off-by: Sami Tolvanen <[email protected]>
>
> Thanks for fixing this!
>
> Acked-by: Kees Cook <[email protected]>
>
> I wonder if there is any compiler option we can turn on to catch the
> implicit enum/int casting that would help for these kinds of things
> without absolutely exploding the build warnings.
>
> I see -Wenum-conversion, but that seems to be between enums, not between
> int.
>
> I see this, but it's external:
> https://noamlewis.wordpress.com/2017/10/05/type-safe-enums-in-c-using-a-clang-plugin/
Unfortunately, using a looser integral type is the typical workaround
for -Wenum-conversion warnings (which is on by default, GCC recently
added that flag, too). For warning on enum to int, the kernel would
probably blow up with warnings. I don't know of any such existing
warning flag.
>
> -Kees
>
> > ---
> > include/linux/lsm_hook_defs.h | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
> > index 6791813cd439..24f6683f1cfc 100644
> > --- a/include/linux/lsm_hook_defs.h
> > +++ b/include/linux/lsm_hook_defs.h
> > @@ -360,7 +360,7 @@ LSM_HOOK(int, 0, key_alloc, struct key *key, const struct cred *cred,
> > unsigned long flags)
> > LSM_HOOK(void, LSM_RET_VOID, key_free, struct key *key)
> > LSM_HOOK(int, 0, key_permission, key_ref_t key_ref, const struct cred *cred,
> > - unsigned perm)
> > + enum key_need_perm need_perm)
> > LSM_HOOK(int, 0, key_getsecurity, struct key *key, char **_buffer)
> > #endif /* CONFIG_KEYS */
> >
> >
> > base-commit: b3a9e3b9622ae10064826dccb4f7a52bd88c7407
> > --
> > 2.27.0.290.gba653c62da-goog
> >
>
> --
> Kees Cook
>
> --
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--
Thanks,
~Nick Desaulniers
On Mon, Jun 15, 2020 at 11:23:44AM -0700, Nick Desaulniers wrote:
> On Mon, Jun 15, 2020 at 11:21 AM Kees Cook <[email protected]> wrote:
> >
> > On Mon, Jun 15, 2020 at 11:12:32AM -0700, Sami Tolvanen wrote:
> > > Commit 8c0637e950d6 ("keys: Make the KEY_NEED_* perms an enum rather than
> > > a mask") changed the type of the key_permission callback functions, but
> > > didn't change the type of the hook, which trips indirect call checking with
> > > Control-Flow Integrity (CFI). This change fixes the issue by changing the
> > > hook type to match the functions.
> > >
> > > Fixes: 8c0637e950d6 ("keys: Make the KEY_NEED_* perms an enum rather than a mask")
> > > Signed-off-by: Sami Tolvanen <[email protected]>
> >
> > Thanks for fixing this!
> >
> > Acked-by: Kees Cook <[email protected]>
> >
> > I wonder if there is any compiler option we can turn on to catch the
> > implicit enum/int casting that would help for these kinds of things
> > without absolutely exploding the build warnings.
> >
> > I see -Wenum-conversion, but that seems to be between enums, not between
> > int.
> >
> > I see this, but it's external:
> > https://noamlewis.wordpress.com/2017/10/05/type-safe-enums-in-c-using-a-clang-plugin/
>
> Unfortunately, using a looser integral type is the typical workaround
> for -Wenum-conversion warnings (which is on by default, GCC recently
> added that flag, too). For warning on enum to int, the kernel would
> probably blow up with warnings. I don't know of any such existing
> warning flag.
Yeah, I couldn't find anything either. The closest I could find to avoid
one of the common classes of enum -> int conversion is the bitwise
operations, which is covered by __attribute__((flag_enum)):
https://clang.llvm.org/docs/AttributeReference.html#flag-enum
Ah well. We'll let CFI find them. ;)
--
Kees Cook
On Mon, Jun 15, 2020 at 11:12:32AM -0700, Sami Tolvanen wrote:
> Commit 8c0637e950d6 ("keys: Make the KEY_NEED_* perms an enum rather than
> a mask") changed the type of the key_permission callback functions, but
> didn't change the type of the hook, which trips indirect call checking with
> Control-Flow Integrity (CFI). This change fixes the issue by changing the
> hook type to match the functions.
>
> Fixes: 8c0637e950d6 ("keys: Make the KEY_NEED_* perms an enum rather than a mask")
> Signed-off-by: Sami Tolvanen <[email protected]>
> ---
> include/linux/lsm_hook_defs.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
> index 6791813cd439..24f6683f1cfc 100644
> --- a/include/linux/lsm_hook_defs.h
> +++ b/include/linux/lsm_hook_defs.h
> @@ -360,7 +360,7 @@ LSM_HOOK(int, 0, key_alloc, struct key *key, const struct cred *cred,
> unsigned long flags)
> LSM_HOOK(void, LSM_RET_VOID, key_free, struct key *key)
> LSM_HOOK(int, 0, key_permission, key_ref_t key_ref, const struct cred *cred,
> - unsigned perm)
> + enum key_need_perm need_perm)
> LSM_HOOK(int, 0, key_getsecurity, struct key *key, char **_buffer)
> #endif /* CONFIG_KEYS */
>
>
> base-commit: b3a9e3b9622ae10064826dccb4f7a52bd88c7407
David, James? Can someone please take this?
--
Kees Cook
On Mon, 15 Jun 2020, Sami Tolvanen wrote:
> Commit 8c0637e950d6 ("keys: Make the KEY_NEED_* perms an enum rather than
> a mask") changed the type of the key_permission callback functions, but
> didn't change the type of the hook, which trips indirect call checking with
> Control-Flow Integrity (CFI). This change fixes the issue by changing the
> hook type to match the functions.
>
> Fixes: 8c0637e950d6 ("keys: Make the KEY_NEED_* perms an enum rather than a mask")
> Signed-off-by: Sami Tolvanen <[email protected]>
Applied to
git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security.git fixes-v5.8
NOTE: please cc: the LSM list with patches such as these.
--
James Morris
<[email protected]>