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UPSTREAM: bpf: Fix stackmap overflow check on 32-bit arches

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[ 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()")
Change-Id: Id67d50b83af553ac5c1087ebded62c4526e95235
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>
This commit is contained in:
Toke Høiland-Jørgensen
2024-03-07 13:03:37 +01:00
committed by bengris32
parent 82d4befc18
commit 9c88ef1085
1 changed files with 0 additions and 2 deletions
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kernel/bpf/stackmap.c
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@@ -122,8 +122,6 @@ static struct bpf_map *stack_map_alloc(union bpf_attr *attr)
return ERR_PTR(-E2BIG);
n_buckets = roundup_pow_of_two(attr->max_entries);
if (!n_buckets)
return ERR_PTR(-E2BIG);
cost = n_buckets * sizeof(struct stack_map_bucket *) + sizeof(*smap);
err = bpf_map_charge_init(&mem, cost + attr->max_entries *