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bpf: Fix hashtab overflow check on 32-bit arches
[ Upstream commit6787d916c2
] The hashtab 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. So apply the same fix to hashtab, by moving the overflow check to before the roundup. Fixes:daaf427c6a
("bpf: fix arraymap NULL deref and missing overflow and zero size checks") Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com> Message-ID: <20240307120340.99577-3-toke@redhat.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Sasha Levin <sashal@kernel.org>
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1 changed files with 9 additions and 5 deletions
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@ -495,7 +495,13 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
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num_possible_cpus());
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num_possible_cpus());
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}
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}
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/* hash table size must be power of 2 */
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/* hash table size must be power of 2; roundup_pow_of_two() can overflow
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* into UB on 32-bit arches, so check that first
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*/
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err = -E2BIG;
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if (htab->map.max_entries > 1UL << 31)
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goto free_htab;
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htab->n_buckets = roundup_pow_of_two(htab->map.max_entries);
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htab->n_buckets = roundup_pow_of_two(htab->map.max_entries);
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htab->elem_size = sizeof(struct htab_elem) +
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htab->elem_size = sizeof(struct htab_elem) +
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@ -505,10 +511,8 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
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else
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else
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htab->elem_size += round_up(htab->map.value_size, 8);
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htab->elem_size += round_up(htab->map.value_size, 8);
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err = -E2BIG;
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/* check for u32 overflow */
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/* prevent zero size kmalloc and check for u32 overflow */
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if (htab->n_buckets > U32_MAX / sizeof(struct bucket))
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if (htab->n_buckets == 0 ||
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htab->n_buckets > U32_MAX / sizeof(struct bucket))
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goto free_htab;
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goto free_htab;
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err = -ENOMEM;
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err = -ENOMEM;
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