From: Krzesimir Nowak krzesimir@kinvolk.io
[ Upstream commit e2f7fc0ac6957cabff4cecf6c721979b571af208 ]
Commit 31fd85816dbe ("bpf: permits narrower load from bpf program context fields") made the verifier add AND instructions to clear the unwanted bits with a mask when doing a narrow load. The mask is computed with
(1 << size * 8) - 1
where "size" is the size of the narrow load. When doing a 4 byte load of a an 8 byte field the verifier shifts the literal 1 by 32 places to the left. This results in an overflow of a signed integer, which is an undefined behavior. Typically, the computed mask was zero, so the result of the narrow load ended up being zero too.
Cast the literal to long long to avoid overflows. Note that narrow load of the 4 byte fields does not have the undefined behavior, because the load size can only be either 1 or 2 bytes, so shifting 1 by 8 or 16 places will not overflow it. And reading 4 bytes would not be a narrow load of a 4 bytes field.
Fixes: 31fd85816dbe ("bpf: permits narrower load from bpf program context fields") Reviewed-by: Alban Crequy alban@kinvolk.io Reviewed-by: Iago López Galeiras iago@kinvolk.io Signed-off-by: Krzesimir Nowak krzesimir@kinvolk.io Cc: Yonghong Song yhs@fb.com Signed-off-by: Daniel Borkmann daniel@iogearbox.net Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/bpf/verifier.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 09d5d972c9ff2..950fac024fbb1 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -7296,7 +7296,7 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env) insn->dst_reg, shift); insn_buf[cnt++] = BPF_ALU64_IMM(BPF_AND, insn->dst_reg, - (1 << size * 8) - 1); + (1ULL << size * 8) - 1); } }