[PATCH v2] apparmor: secid: fix error return value in error handling path

[Gustavo A. R. Silva]

Currently, function apparmor_secid_to_secctx returns always zero,
no matter if the value returned by aa_label_asxprint is negative
(which implies that an error has occurred).

Notice that *seclen* is of type u32 (32 bits, unsigned), and a
less-than-zero comparison of an unsigned value is never true.

Fix this by temporarily storing the value returned by aa_label_asxprint
into a variable of type int (signed) for its further evaluation.

Addresses-Coverity-ID: 1468514 ("Unsigned compared against 0")
Fixes: c092921219d2 ("apparmor: add support for mapping secids and using
secctxes")
Signed-off-by: Gustavo A. R. Silva <gustavo@xxxxxxxxxxxxxx>
---
Changes is v2:
 - Update changelog.
 - Fix misaligned lines.

 security/apparmor/secid.c | 23 ++++++++++++++---------
 1 file changed, 14 insertions(+), 9 deletions(-)

diff --git a/security/apparmor/secid.c b/security/apparmor/secid.c
index 5029248..efaa0d9 100644
--- a/security/apparmor/secid.c
+++ b/security/apparmor/secid.c
@@ -142,6 +142,7 @@ int apparmor_secid_to_secctx(u32 secid, char **secdata, u32 *seclen)
 {
 	/* TODO: cache secctx and ref count so we don't have to recreate */
 	struct aa_label *label = aa_secid_to_label(secid);
+	int seclen_tmp;
 
 	AA_BUG(!secdata);
 	AA_BUG(!seclen);
@@ -150,17 +151,21 @@ int apparmor_secid_to_secctx(u32 secid, char **secdata, u32 *seclen)
 		return -EINVAL;
 
 	if (secdata)
-		*seclen = aa_label_asxprint(secdata, root_ns, label,
-					    FLAG_SHOW_MODE | FLAG_VIEW_SUBNS |
-					    FLAG_HIDDEN_UNCONFINED |
-					    FLAG_ABS_ROOT, GFP_ATOMIC);
+		seclen_tmp = aa_label_asxprint(secdata, root_ns, label,
+					       FLAG_SHOW_MODE |
+					       FLAG_VIEW_SUBNS |
+					       FLAG_HIDDEN_UNCONFINED |
+					       FLAG_ABS_ROOT, GFP_ATOMIC);
 	else
-		*seclen = aa_label_snxprint(NULL, 0, root_ns, label,
-					    FLAG_SHOW_MODE | FLAG_VIEW_SUBNS |
-					    FLAG_HIDDEN_UNCONFINED |
-					    FLAG_ABS_ROOT);
-	if (*seclen < 0)
+		seclen_tmp = aa_label_snxprint(NULL, 0, root_ns, label,
+					       FLAG_SHOW_MODE |
+					       FLAG_VIEW_SUBNS |
+					       FLAG_HIDDEN_UNCONFINED |
+					       FLAG_ABS_ROOT);
+	if (seclen_tmp < 0)
 		return -ENOMEM;
+	else
+		*seclen = seclen_tmp;
 
 	return 0;
 }
-- 
2.7.4