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

[John Johansen <john.johansen@canonical.com>]

On 8/10/26 02:51, Hyunwoo Kim wrote:
> 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: stable@vger.kernel.org
> Signed-off-by: Hyunwoo Kim <imv4bel@gmail.com>

Acked-by: John Johansen <john.johansen@canonical.com>

I have pulled this into my tree

> ---
>   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;						\
>   })
>