[PATCH] apparmor: fix out-of-bounds write when null terminating a label vec

aa_vec_unique() null terminates at vec[n - dups] when VEC_FLAG_TERMINATE
is passed. If the components are all distinct no duplicates are dropped,
dups is 0 and the terminator goes to vec[n], so the caller has to provide
room for n + 1 entries.

aa_label_strn_parse() sets up its vector with vec_setup(profile, vec, len,
gfp) and then calls aa_vec_unique(vec, len, VEC_FLAG_TERMINATE), but
vec_setup() does not reserve the terminator entry. Up to LOCAL_VEC_ENTRIES
it uses the local array of LOCAL_VEC_ENTRIES pointers, above that it
allocates exactly len pointers. The terminator therefore lands one entry
past the end of the local array when len is LOCAL_VEC_ENTRIES, and one
entry past the end of the allocation when len is larger.

len comes from the number of "//&" separated components in the label name
and label_count_strn_entries() does not bound it. An unprivileged task
reaches the parse by writing to /proc/self/attr/apparmor/current or through
lsm_set_self_attr(2), both of which go through do_setattr(), and the name
is parsed before the change_profile permission is checked.
The query_label() path behind the securityfs .access file, which is
mode 0666, performs no permission check at all. Every component has to
resolve to a loaded profile, so a system with policy loaded is required.

The other two VEC_FLAG_TERMINATE users work on a label vec that
aa_label_alloc() has already sized with "+ 1 for null terminator entry on
vec". Reserve the same entry in vec_setup() and DEFINE_VEC(). Passing
len + 1 from the caller instead would move len == LOCAL_VEC_ENTRIES out of
the local array and into kzalloc().

Fixes: f1bd904175e8 ("apparmor: add the base fns() for domain labels")
Cc: [email protected]
Signed-off-by: Hyunwoo Kim <[email protected]>
---
 security/apparmor/include/label.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/security/apparmor/include/label.h b/security/apparmor/include/label.h
index b5a722a47fd2c8..37cb135de32320 100644
--- a/security/apparmor/include/label.h
+++ b/security/apparmor/include/label.h
@@ -23,7 +23,7 @@ struct aa_ruleset;
 
 #define LOCAL_VEC_ENTRIES 8
 #define DEFINE_VEC(T, V)						\
-	struct aa_ ## T *(_ ## V ## _localtmp)[LOCAL_VEC_ENTRIES];	\
+	struct aa_ ## T *(_ ## V ## _localtmp)[LOCAL_VEC_ENTRIES + 1];	\
 	struct aa_ ## T **(V)
 
 #define vec_setup(T, V, N, GFP)						\
@@ -31,10 +31,10 @@ struct aa_ruleset;
 	if ((N) <= LOCAL_VEC_ENTRIES) {					\
 		typeof(N) i;						\
 		(V) = (_ ## V ## _localtmp);				\
-		for (i = 0; i < (N); i++)				\
+		for (i = 0; i <= (N); i++)				\
 			(V)[i] = NULL;					\
 	} else								\
-		(V) = kzalloc(sizeof(struct aa_ ## T *) * (N), (GFP));	\
+		(V) = kzalloc_objs(struct aa_ ## T *, (N) + 1, (GFP));	\
 	(V) ? 0 : -ENOMEM;						\
 })
 
-- 
2.43.0