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bpf: Fix verifier jsgt branch analysis on max bound

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Fix incorrect is_branch{32,64}_taken() analysis for the jsgt case. The return
code for both will tell the caller whether a given conditional jump is taken
or not, e.g. 1 means branch will be taken [for the involved registers] and the
goto target will be executed, 0 means branch will not be taken and instead we
fall-through to the next insn, and last but not least a -1 denotes that it is
not known at verification time whether a branch will be taken or not. Now while
the jsgt has the branch-taken case correct with reg->s32_min_value > sval, the
branch-not-taken case is off-by-one when testing for reg->s32_max_value < sval
since the branch will also be taken for reg->s32_max_value == sval. The jgt
branch analysis, for example, gets this right.

Fixes: 3f50f132d8 ("bpf: Verifier, do explicit ALU32 bounds tracking")
Fixes: 4f7b3e8258 ("bpf: improve verifier branch analysis")
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Daniel Borkmann 2021-02-05 17:20:14 +01:00
parent 6183f4d3a0
commit ee114dd64c
1 changed files with 2 additions and 2 deletions
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4
kernel/bpf/verifier.c
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@ -6877,7 +6877,7 @@ static int is_branch32_taken(struct bpf_reg_state *reg, u32 val, u8 opcode)
case BPF_JSGT:
if (reg->s32_min_value > sval)
return 1;
else if (reg->s32_max_value < sval)
else if (reg->s32_max_value <= sval)
return 0;
break;
case BPF_JLT:
@ -6950,7 +6950,7 @@ static int is_branch64_taken(struct bpf_reg_state *reg, u64 val, u8 opcode)
case BPF_JSGT:
if (reg->smin_value > sval)
return 1;
else if (reg->smax_value < sval)
else if (reg->smax_value <= sval)
return 0;
break;
case BPF_JLT: