From: Toke Høiland-Jørgensen toke@redhat.com
[ Upstream commit 7a4b21250bf79eef26543d35bd390448646c536b ]
The stackmap code relies on roundup_pow_of_two() to compute the number of hash buckets, and contains an overflow check by checking if the resulting value is 0. However, on 32-bit arches, the roundup code itself can overflow by doing a 32-bit left-shift of an unsigned long value, which is undefined behaviour, so it is not guaranteed to truncate neatly. This was triggered by syzbot on the DEVMAP_HASH type, which contains the same check, copied from the hashtab code.
The commit in the fixes tag actually attempted to fix this, but the fix did not account for the UB, so the fix only works on CPUs where an overflow does result in a neat truncation to zero, which is not guaranteed. Checking the value before rounding does not have this problem.
Fixes: 6183f4d3a0a2 ("bpf: Check for integer overflow when using roundup_pow_of_two()") Signed-off-by: Toke Høiland-Jørgensen toke@redhat.com Reviewed-by: Bui Quang Minh minhquangbui99@gmail.com Message-ID: 20240307120340.99577-4-toke@redhat.com Signed-off-by: Alexei Starovoitov ast@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/bpf/stackmap.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c index b8afea2ceeeb1..3ec76cb5f240d 100644 --- a/kernel/bpf/stackmap.c +++ b/kernel/bpf/stackmap.c @@ -115,11 +115,14 @@ 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); err = bpf_map_charge_init(&mem, cost + attr->max_entries * (sizeof(struct stack_map_bucket) + (u64)value_size));