apparmor: fix absroot causing audited secids to begin with =

stable inclusion
from stable-v5.10.138
commit 08f8128bc9f2b4489e8dd84b91cb69abc0b9c963
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I60QFD

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=08f8128bc9f2b4489e8dd84b91cb69abc0b9c963

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

commit 511f7b5b upstream.

AppArmor is prefixing secids that are converted to secctx with the =
to indicate the secctx should only be parsed from an absolute root
POV. This allows catching errors where secctx are reparsed back into
internal labels.

Unfortunately because audit is using secid to secctx conversion this
means that subject and object labels can result in a very unfortunate
== that can break audit parsing.

eg. the subj==unconfined term in the below audit message

type=USER_LOGIN msg=audit(1639443365.233:160): pid=1633 uid=0 auid=1000
ses=3 subj==unconfined msg='op=login id=1000 exe="/usr/sbin/sshd"
hostname=192.168.122.1 addr=192.168.122.1 terminal=/dev/pts/1 res=success'

Fix this by switch the prepending of = to a _. This still works as a
special character to flag this case without breaking audit. Also move
this check behind debug as it should not be needed during normal
operqation.

Fixes: 26b78995 ("apparmor: add support for absolute root view based labels")
Reported-by: NCasey Schaufler <casey@schaufler-ca.com>
Signed-off-by: NJohn Johansen <john.johansen@canonical.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>
Reviewed-by: NWei Li <liwei391@huawei.com>

security/apparmor/include/lib.h

@@ -22,6 +22,11 @@
  */
 
 #define DEBUG_ON (aa_g_debug)
+/*
+ * split individual debug cases out in preparation for finer grained
+ * debug controls in the future.
+ */
+#define AA_DEBUG_LABEL DEBUG_ON
 #define dbg_printk(__fmt, __args...) pr_debug(__fmt, ##__args)
 #define AA_DEBUG(fmt, args...)						\
 	do {								\

security/apparmor/label.c

@@ -1632,9 +1632,9 @@ int aa_label_snxprint(char *str, size_t size, struct aa_ns *ns,
 	AA_BUG(!str && size != 0);
 	AA_BUG(!label);
 
-	if (flags & FLAG_ABS_ROOT) {
+	if (AA_DEBUG_LABEL && (flags & FLAG_ABS_ROOT)) {
 		ns = root_ns;
-		len = snprintf(str, size, "=");
+		len = snprintf(str, size, "_");
 		update_for_len(total, len, size, str);
 	} else if (!ns) {
 		ns = labels_ns(label);
@@ -1896,7 +1896,8 @@ struct aa_label *aa_label_strn_parse(struct aa_label *base, const char *str,
 	AA_BUG(!str);
 
 	str = skipn_spaces(str, n);
-	if (str == NULL || (*str == '=' && base != &root_ns->unconfined->label))
+	if (str == NULL || (AA_DEBUG_LABEL && *str == '_' &&
+			    base != &root_ns->unconfined->label))
 		return ERR_PTR(-EINVAL);
 
 	len = label_count_strn_entries(str, end - str);