[bug report] apparmor: add support loading per permission tagging

[bug report] apparmor: add support loading per permission tagging

[Dan Carpenter]

[ Smatch checking is paused while we raise funding. #SadFace
  https://lore.kernel.org/all/aTaiGSbWZ9DJaGo7@stanley.mountain/ -dan ]

Hello John Johansen,

Commit 3d28e2397af7 ("apparmor: add support loading per permission
tagging") from Apr 1, 2025 (linux-next), leads to the following
Smatch static checker warning:

	security/apparmor/policy_unpack.c:966 unpack_pdb()
	warn: unsigned 'unpack_tags(e, &pdb->tags, info)' is never less than zero.

security/apparmor/policy_unpack.c
    951 static int unpack_pdb(struct aa_ext *e, struct aa_policydb **policy,
    952                       bool required_dfa, bool required_trans,
    953                       const char **info)
    954 {
    955         struct aa_policydb *pdb;
    956         void *pos = e->pos;
    957         int i, flags, error = -EPROTO;
    958         ssize_t size;
    959         u32 version = 0;
    960 
    961         pdb = aa_alloc_pdb(GFP_KERNEL);
    962         if (!pdb)
    963                 return -ENOMEM;
    964 
    965         AA_DEBUG(DEBUG_UNPACK, "unpacking tags");
--> 966         if (unpack_tags(e, &pdb->tags, info) < 0)
                    ^^^^^^^^^^^
Signedness bug.  unpack_tags() is unsigned.

    967                 goto fail;
    968         AA_DEBUG(DEBUG_UNPACK, "done unpacking tags");
    969 
    970         size = unpack_perms_table(e, &pdb->perms);
    971         if (size < 0) {
    972                 error = size;
    973                 pdb->perms = NULL;

regards,
dan carpenter

[apparmor][PATCH] apparmor: fix signedness bug in unpack_tags()

[Massimiliano Pellizzer]

Smatch static checker warning:
    security/apparmor/policy_unpack.c:966 unpack_pdb()
    warn: unsigned 'unpack_tags(e, &pdb->tags, info)' is never less than zero.

unpack_tags() is declared with return type size_t (unsigned) but returns
negative errno values on failure. The caller in unpack_pdb() tests the
return with `< 0`, which is always false for an unsigned type, making
error handling dead code. Malformed tag data would be silently accepted
instead of causing a load failure.

Change return type of unpack_tags() from size_t to int to match the
functions's actual semantic.

Fixes: 3d28e2397af7 ("apparmor: add support loading per permission tagging")
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Massimiliano Pellizzer <mpellizzer.dev@gmail.com>
---
 security/apparmor/policy_unpack.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/security/apparmor/policy_unpack.c b/security/apparmor/policy_unpack.c
index e68adf39771f..dc908e1f5a88 100644
--- a/security/apparmor/policy_unpack.c
+++ b/security/apparmor/policy_unpack.c
@@ -835,7 +835,7 @@ static int unpack_tag_headers(struct aa_ext *e, struct aa_tags_struct *tags)
 }
 
 
-static size_t unpack_tags(struct aa_ext *e, struct aa_tags_struct *tags,
+static int unpack_tags(struct aa_ext *e, struct aa_tags_struct *tags,
 	const char **info)
 {
 	int error = -EPROTO;
-- 
2.51.0