capability: just use a 'u64' instead of a 'u32[2]' array

Back in 2008 we extended the capability bits from 32 to 64, and we did
it by extending the single 32-bit capability word from one word to an
array of two words.  It was then obfuscated by hiding the "2" behind two
macro expansions, with the reasoning being that maybe it gets extended
further some day.

That reasoning may have been valid at the time, but the last thing we
want to do is to extend the capability set any more.  And the array of
values not only causes source code oddities (with loops to deal with
it), but also results in worse code generation.  It's a lose-lose
situation.

So just change the 'u32[2]' into a 'u64' and be done with it.

We still have to deal with the fact that the user space interface is
designed around an array of these 32-bit values, but that was the case
before too, since the array layouts were different (ie user space
doesn't use an array of 32-bit values for individual capability masks,
but an array of 32-bit slices of multiple masks).

So that marshalling of data is actually simplified too, even if it does
remain somewhat obscure and odd.

This was all triggered by my reaction to the new "cap_isidentical()"
introduced recently.  By just using a saner data structure, it went from

	unsigned __capi;
	CAP_FOR_EACH_U32(__capi) {
		if (a.cap[__capi] != b.cap[__capi])
			return false;
	}
	return true;

to just being

	return a.val == b.val;

instead.  Which is rather more obvious both to humans and to compilers.

Cc: Mateusz Guzik <mjguzik@gmail.com>
Cc: Casey Schaufler <casey@schaufler-ca.com>
Cc: Serge Hallyn <serge@hallyn.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Paul Moore <paul@paul-moore.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 30 insertions, 10 deletions

diff --git a/security/apparmor/policy_unpack.c b/security/apparmor/policy_unpack.c
index 5e9949832af62..cf2ceec40b28a 100644
--- a/security/apparmor/policy_unpack.c
+++ b/security/apparmor/policy_unpack.c
@@ -304,6 +304,26 @@ fail:
 }
 EXPORT_SYMBOL_IF_KUNIT(aa_unpack_u64);
 
+static bool aa_unpack_cap_low(struct aa_ext *e, kernel_cap_t *data, const char *name)
+{
+	u32 val;
+
+	if (!aa_unpack_u32(e, &val, name))
+		return false;
+	data->val = val;
+	return true;
+}
+
+static bool aa_unpack_cap_high(struct aa_ext *e, kernel_cap_t *data, const char *name)
+{
+	u32 val;
+
+	if (!aa_unpack_u32(e, &val, name))
+		return false;
+	data->val = (u32)data->val | ((u64)val << 32);
+	return true;
+}
+
 VISIBLE_IF_KUNIT bool aa_unpack_array(struct aa_ext *e, const char *name, u16 *size)
 {
 	void *pos = e->pos;
@@ -897,25 +917,25 @@ static struct aa_profile *unpack_profile(struct aa_ext *e, char **ns_name)
 		profile->path_flags = PATH_MEDIATE_DELETED;
 
 	info = "failed to unpack profile capabilities";
-	if (!aa_unpack_u32(e, &(rules->caps.allow.cap[0]), NULL))
+	if (!aa_unpack_cap_low(e, &rules->caps.allow, NULL))
 		goto fail;
-	if (!aa_unpack_u32(e, &(rules->caps.audit.cap[0]), NULL))
+	if (!aa_unpack_cap_low(e, &rules->caps.audit, NULL))
 		goto fail;
-	if (!aa_unpack_u32(e, &(rules->caps.quiet.cap[0]), NULL))
+	if (!aa_unpack_cap_low(e, &rules->caps.quiet, NULL))
 		goto fail;
-	if (!aa_unpack_u32(e, &tmpcap.cap[0], NULL))
+	if (!aa_unpack_cap_low(e, &tmpcap, NULL))
 		goto fail;
 
 	info = "failed to unpack upper profile capabilities";
 	if (aa_unpack_nameX(e, AA_STRUCT, "caps64")) {
 		/* optional upper half of 64 bit caps */
-		if (!aa_unpack_u32(e, &(rules->caps.allow.cap[1]), NULL))
+		if (!aa_unpack_cap_high(e, &rules->caps.allow, NULL))
 			goto fail;
-		if (!aa_unpack_u32(e, &(rules->caps.audit.cap[1]), NULL))
+		if (!aa_unpack_cap_high(e, &rules->caps.audit, NULL))
 			goto fail;
-		if (!aa_unpack_u32(e, &(rules->caps.quiet.cap[1]), NULL))
+		if (!aa_unpack_cap_high(e, &rules->caps.quiet, NULL))
 			goto fail;
-		if (!aa_unpack_u32(e, &(tmpcap.cap[1]), NULL))
+		if (!aa_unpack_cap_high(e, &tmpcap, NULL))
 			goto fail;
 		if (!aa_unpack_nameX(e, AA_STRUCTEND, NULL))
 			goto fail;
@@ -924,9 +944,9 @@ static struct aa_profile *unpack_profile(struct aa_ext *e, char **ns_name)
 	info = "failed to unpack extended profile capabilities";
 	if (aa_unpack_nameX(e, AA_STRUCT, "capsx")) {
 		/* optional extended caps mediation mask */
-		if (!aa_unpack_u32(e, &(rules->caps.extended.cap[0]), NULL))
+		if (!aa_unpack_cap_low(e, &rules->caps.extended, NULL))
 			goto fail;
-		if (!aa_unpack_u32(e, &(rules->caps.extended.cap[1]), NULL))
+		if (!aa_unpack_cap_high(e, &rules->caps.extended, NULL))
 			goto fail;
 		if (!aa_unpack_nameX(e, AA_STRUCTEND, NULL))
 			goto fail;