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Bufferoverrun Analysis - small fixes and improvements #1736

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Bufferoverrun Analysis - small fixes and improvements #1736

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31ab607
[inferbo] Fix an ignored case when the upper bounds of offset is +oo,…
sjxer723 Feb 3, 2023
fd0a4e6
[inferbo] Make a more precise upper/lower bound when adding two upper…
sjxer723 Feb 6, 2023
347d391
[inferbo] Initialize locations for arrays within struct typed variables
sjxer723 Feb 24, 2023
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24 changes: 12 additions & 12 deletions infer/src/bufferoverrun/bounds.ml
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Expand Up @@ -950,25 +950,25 @@ module Bound = struct
let plus_l : weak:bool -> t -> t -> t =
plus_exact ~otherwise:(fun x y ->
match (x, y) with
| MinMax (c1, Plus, Max, d1, _), Linear (c2, x2)
| Linear (c2, x2), MinMax (c1, Plus, Max, d1, _) ->
Linear (Z.(c1 + d1 + c2), x2)
| MinMax (c1, Minus, Min, d1, _), Linear (c2, x2)
| Linear (c2, x2), MinMax (c1, Minus, Min, d1, _) ->
Linear (Z.(c1 - d1 + c2), x2)
| MinMax (c1, Plus, Max, d1, x1), Linear (c2, x2)
| Linear (c2, x2), MinMax (c1, Plus, Max, d1, x1) ->
mk_MinMaxB (Max, (Linear (Z.(c1 + d1 + c2), x2)), (Linear (Z.(c1 + c2), SymLinear.plus (SymLinear.singleton_one x1) x2)))
| MinMax (c1, Minus, Min, d1, x1), Linear (c2, x2)
| Linear (c2, x2), MinMax (c1, Minus, Min, d1, x1) ->
mk_MinMaxB (Max, (Linear (Z.(c1 - d1 + c2), x2)), (Linear (Z.(c1 + c2), SymLinear.plus (SymLinear.singleton_minus_one x1) x2)))
Comment on lines +953 to +958
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While MinMaxB was introduced to express more complex min/max expressions, it is NOT always a better choice than others. By its complex nature, many operations may easily lose precision on MinMaxB bound, for example, during widening it is more likely to have infinity bounds according to my experience. Therefore, if we want to introduce MinMaxB here for the plus operation, we should evaluate overall precision impacts. Let me check if it is fine for our use cases.

| _, _ ->
MInf )


let plus_u : weak:bool -> t -> t -> t =
plus_exact ~otherwise:(fun x y ->
match (x, y) with
| MinMax (c1, Plus, Min, d1, _), Linear (c2, x2)
| Linear (c2, x2), MinMax (c1, Plus, Min, d1, _) ->
Linear (Z.(c1 + d1 + c2), x2)
| MinMax (c1, Minus, Max, d1, _), Linear (c2, x2)
| Linear (c2, x2), MinMax (c1, Minus, Max, d1, _) ->
Linear (Z.(c1 - d1 + c2), x2)
| MinMax (c1, Plus, Min, d1, x1), Linear (c2, x2)
| Linear (c2, x2), MinMax (c1, Plus, Min, d1, x1) ->
mk_MinMaxB (Min, (Linear (Z.(c1 + d1 + c2), x2)), (Linear (Z.(c1 + c2), SymLinear.plus (SymLinear.singleton_one x1) x2)))
| MinMax (c1, Minus, Max, d1, x1), Linear (c2, x2)
| Linear (c2, x2), MinMax (c1, Minus, Max, d1, x1) ->
mk_MinMaxB (Min, (Linear (Z.(c1 - d1 + c2), x2)), (Linear (Z.(c1 + c2), SymLinear.plus (SymLinear.singleton_minus_one x1) x2)))
| _, _ ->
PInf )

Expand Down
4 changes: 4 additions & 0 deletions infer/src/bufferoverrun/bufferOverrunProofObligations.ml
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Expand Up @@ -347,6 +347,10 @@ module ArrayAccessCondition = struct
Bound.is_not_infty (ItvPure.ub real_idx) && Bound.le (ItvPure.ub size) (ItvPure.ub real_idx)
then {report_issue_type= Issue IssueType.buffer_overrun_l2; propagate= false}
(* symbolic il >= sl, probably an error *)
else if
Bound.is_infty (ItvPure.ub real_idx) && Bound.is_not_infty (ItvPure.ub size)
then {report_issue_type= Issue IssueType.buffer_overrun_l3; propagate= false}
(* su < iu = +oo, probably an error *)
Comment on lines +350 to +353
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@skcho skcho Feb 28, 2023 •
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However, this error was missed by buffer overrun checker.

a.c:4: error: Buffer Overrun L4
  Offset: [0, +oo] Size: 2.
  2. void foo() {
  3. int a[2];
  4. for(int i=0; a[i]; i++) {}
                  ^
  5. }

For the example case, it reports L4 issue as above. The reason you did not see the issue is that it suppresses the issue types that are likely to be false positive, e.g. offset or size interval includes an infinity bound like above.

infer/infer/src/base/IssueType.ml

Lines 380 to 382 in 5aeb169

let buffer_overrun_l4 =
register ~enabled:false ~id:"BUFFER_OVERRUN_L4" Error BufferOverrunChecker
~user_documentation:"See [BUFFER_OVERRUN_L1](#buffer_overrun_l1)"

Note that ~enabled:false is given when defining the L4 issue type.

To enable all issue types, you can pass --no-filtering option, or --enable-issue-type to enable each of them.

else if
Bound.is_symbolic (ItvPure.lb real_idx) && Bound.le (ItvPure.lb size) (ItvPure.lb real_idx)
then {report_issue_type= Issue IssueType.buffer_overrun_s2; propagate= true}
Expand Down
26 changes: 25 additions & 1 deletion infer/src/bufferoverrun/bufferOverrunUtils.ml
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Expand Up @@ -16,6 +16,7 @@ module Sem = BufferOverrunSemantics
module Trace = BufferOverrunTrace
module TraceSet = Trace.Set
module TypModels = BufferOverrunTypModels
module BoField = BufferOverrunField

module ModelEnv = struct
type model_env =
Expand Down Expand Up @@ -52,14 +53,37 @@ module Exec = struct
mem


let rec decl_local_loc ({tenv} as model_env) loc typ ~inst_num ~represents_multiple_values
let rec decl_local_struct_fields_loc: ModelEnv.model_env -> Loc.t -> Struct.fields -> Dom.Mem.t * int -> Dom.Mem.t * int =
fun model_env loc fields (mem, inst_num) ->
match fields with
| field :: tl -> (
match field with
| (fn, typ, _) -> (
match typ.desc with
| Tarray {elt= _; length; stride} ->
let child_loc = BoField.Field {prefix= loc; fn; typ = (Some typ)} in
let stride = Option.map ~f:IntLit.to_int_exn stride in
let (mem, inst_num) = decl_local_array model_env child_loc typ ~length ?stride ~inst_num
~represents_multiple_values:false ~dimension:1 mem
in
decl_local_struct_fields_loc model_env loc tl (mem, inst_num)
| _ -> decl_local_struct_fields_loc model_env loc tl (mem, inst_num)))
| [] -> (mem, inst_num)
and decl_local_loc ({tenv} as model_env) loc typ ~inst_num ~represents_multiple_values
~dimension mem =
match typ.Typ.desc with
| Typ.Tarray {elt= typ; length; stride} ->
let stride = Option.map ~f:IntLit.to_int_exn stride in
decl_local_array model_env loc typ ~length ?stride ~inst_num ~represents_multiple_values
~dimension mem
| Typ.Tstruct typname -> (
let mem = (
match Tenv.lookup tenv typname with
| Some {fields} ->
let (mem, _) = decl_local_struct_fields_loc model_env loc fields (mem, 1) in mem
| None -> mem
)
in
Comment on lines +80 to +86
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I think it is better to pass current dimension and inst_num, to distinguish the allocation sites.

        let mem, inst_num =
          match Tenv.lookup tenv typname with
          | Some {fields} ->
              decl_local_struct_fields_loc model_env loc fields ~inst_num ~dimension mem
          | None ->
              (mem, inst_num)
        in

match TypModels.dispatch tenv typname with
| Some (CArray {element_typ; length}) ->
decl_local_array model_env loc element_typ ~length:(Some length) ~inst_num
Expand Down