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Commit 545722cb authored by Edward Cree's avatar Edward Cree Committed by David S. Miller
Browse files

selftests/bpf: subtraction bounds test 



There is a bug in the verifier's handling of BPF_SUB: [a,b] - [c,d] yields
 was [a-c, b-d] rather than the correct [a-d, b-c].  So here is a test
 which, with the bogus handling, will produce ranges of [0,0] and thus
 allowed accesses; whereas the correct handling will give a range of
 [-255, 255] (and hence the right-shift will give a range of [0, 255]) and
 the accesses will be rejected.

Signed-off-by: default avatarEdward Cree <ecree@solarflare.com>
Acked-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 70dba204

tools/testing/selftests/bpf/test_verifier.c

+28 −0
Original line number Diff line number Diff line
@@ -5980,6 +5980,34 @@ static struct bpf_test tests[] = { 
		.result = REJECT,

		.result_unpriv = REJECT,

	},

	{

		"subtraction bounds (map value)",

		.insns = {

			BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0),

			BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),

			BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8),

			BPF_LD_MAP_FD(BPF_REG_1, 0),

			BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0,

				     BPF_FUNC_map_lookup_elem),

			BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 9),

			BPF_LDX_MEM(BPF_B, BPF_REG_1, BPF_REG_0, 0),

			BPF_JMP_IMM(BPF_JGT, BPF_REG_1, 0xff, 7),

			BPF_LDX_MEM(BPF_B, BPF_REG_3, BPF_REG_0, 1),

			BPF_JMP_IMM(BPF_JGT, BPF_REG_3, 0xff, 5),

			BPF_ALU64_REG(BPF_SUB, BPF_REG_1, BPF_REG_3),

			BPF_ALU64_IMM(BPF_RSH, BPF_REG_1, 56),

			BPF_ALU64_REG(BPF_ADD, BPF_REG_0, BPF_REG_1),

			BPF_LDX_MEM(BPF_B, BPF_REG_0, BPF_REG_0, 0),

			BPF_EXIT_INSN(),

			BPF_MOV64_IMM(BPF_REG_0, 0),

			BPF_EXIT_INSN(),

		},

		.fixup_map1 = { 3 },

		.errstr_unpriv = "R0 pointer arithmetic prohibited",

		.errstr = "R0 min value is negative, either use unsigned index or do a if (index >=0) check.",

		.result = REJECT,

		.result_unpriv = REJECT,

	},

};



static int probe_filter_length(const struct bpf_insn *fp)