Commit a27e8967 authored by Alexei Starovoitov's avatar Alexei Starovoitov
Browse files

Merge branch 'fix-hash-bucket-overflow-checks-for-32-bit-arches' 

Toke Høiland-Jørgensen says:

====================
Fix hash bucket overflow checks for 32-bit arches

Syzbot managed to trigger a crash by creating a DEVMAP_HASH map with a
large number of buckets because the overflow check relies on
well-defined behaviour that is only correct on 64-bit arches.

Fix the overflow checks to happen before values are rounded up in all
the affected map types.

v3:
- Keep the htab->n_buckets > U32_MAX / sizeof(struct bucket) check
- Use 1UL << 31 instead of U32_MAX / 2 + 1 as the constant to check
  against
- Add patch to fix stackmap.c
v2:
- Fix off-by-one error in overflow check
- Apply the same fix to hashtab, where the devmap_hash code was copied
  from (John)

Toke Høiland-Jørgensen (3):
  bpf: Fix DEVMAP_HASH overflow check on 32-bit arches
  bpf: Fix hashtab overflow check on 32-bit arches
  bpf: Fix stackmap overflow check on 32-bit arches

 kernel/bpf/devmap.c   | 11 ++++++-----
 kernel/bpf/hashtab.c  | 14 +++++++++-----
 kernel/bpf/stackmap.c |  9 ++++++---
 3 files changed, 21 insertions(+), 13 deletions(-)
====================

Link: https://lore.kernel.org/r/20240307120340.99577-1-toke@redhat.com


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parents c7d4274e 7a4b2125

kernel/bpf/devmap.c

+6 −5
Original line number Diff line number Diff line
@@ -130,13 +130,14 @@ static int dev_map_init_map(struct bpf_dtab *dtab, union bpf_attr *attr) 
	bpf_map_init_from_attr(&dtab->map, attr);



	if (attr->map_type == BPF_MAP_TYPE_DEVMAP_HASH) {

		dtab->n_buckets = roundup_pow_of_two(dtab->map.max_entries);



		if (!dtab->n_buckets) /* Overflow check */

		/* hash table size must be power of 2; roundup_pow_of_two() can

		 * overflow into UB on 32-bit arches, so check that first

		 */

		if (dtab->map.max_entries > 1UL << 31)

			return -EINVAL;

	}



	if (attr->map_type == BPF_MAP_TYPE_DEVMAP_HASH) {

		dtab->n_buckets = roundup_pow_of_two(dtab->map.max_entries);



		dtab->dev_index_head = dev_map_create_hash(dtab->n_buckets,

							   dtab->map.numa_node);

		if (!dtab->dev_index_head)

kernel/bpf/hashtab.c

+9 −5
Original line number Diff line number Diff line
@@ -499,7 +499,13 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr) 
							  num_possible_cpus());

	}



	/* hash table size must be power of 2 */

	/* hash table size must be power of 2; roundup_pow_of_two() can overflow

	 * into UB on 32-bit arches, so check that first

	 */

	err = -E2BIG;

	if (htab->map.max_entries > 1UL << 31)

		goto free_htab;



	htab->n_buckets = roundup_pow_of_two(htab->map.max_entries);



	htab->elem_size = sizeof(struct htab_elem) +
@@ -509,10 +515,8 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr) 
	else

		htab->elem_size += round_up(htab->map.value_size, 8);



	err = -E2BIG;

	/* prevent zero size kmalloc and check for u32 overflow */

	if (htab->n_buckets == 0 ||

	    htab->n_buckets > U32_MAX / sizeof(struct bucket))

	/* check for u32 overflow */

	if (htab->n_buckets > U32_MAX / sizeof(struct bucket))

		goto free_htab;



	err = bpf_map_init_elem_count(&htab->map);

kernel/bpf/stackmap.c

+6 −3
Original line number Diff line number Diff line
@@ -91,11 +91,14 @@ static struct bpf_map *stack_map_alloc(union bpf_attr *attr) 
	} else if (value_size / 8 > sysctl_perf_event_max_stack)

		return ERR_PTR(-EINVAL);



	/* hash table size must be power of 2 */

	n_buckets = roundup_pow_of_two(attr->max_entries);

	if (!n_buckets)

	/* hash table size must be power of 2; roundup_pow_of_two() can overflow

	 * into UB on 32-bit arches, so check that first

	 */

	if (attr->max_entries > 1UL << 31)

		return ERR_PTR(-E2BIG);



	n_buckets = roundup_pow_of_two(attr->max_entries);



	cost = n_buckets * sizeof(struct stack_map_bucket *) + sizeof(*smap);

	smap = bpf_map_area_alloc(cost, bpf_map_attr_numa_node(attr));

	if (!smap)