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Fix crash when accessing mat[i,j] and mat[i] is unbound #4407

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Apr 19, 2021
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Fix crash when accessing mat[i,j] and mat[i] is unbound #4407

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15 changes: 13 additions & 2 deletions src/lists.c
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Original file line number Diff line number Diff line change
Expand Up @@ -480,14 +480,22 @@ static Obj ElmMatOper;

Obj ELM_MAT(Obj mat, Obj row, Obj col)
{
Obj elm;
if (IS_POS_INTOBJ(row) && IS_POS_INTOBJ(col) && IS_PLIST(mat)) {
Int r = INT_INTOBJ(row);
if (r <= LEN_PLIST(mat)) {
Obj rowlist = ELM_PLIST(mat, r);
Int c = INT_INTOBJ(col);

if (!rowlist)
ErrorMayQuit("Matrix Element: <mat>[%d] must have an assigned value",
(Int)r, (Int)c);
if (IS_PLIST(rowlist) && c <= LEN_PLIST(rowlist)) {
return ELM_PLIST(rowlist, c);
elm = ELM_PLIST(rowlist, c);
if (!elm)
ErrorMayQuit("Matrix Element: <mat>[%d,%d] must have an assigned value",
(Int)r, (Int)c);
return elm;
}

// fallback to generic list access code (also triggers error if
Expand All @@ -496,7 +504,7 @@ Obj ELM_MAT(Obj mat, Obj row, Obj col)
}
}

Obj elm = DoOperation3Args(ElmMatOper, mat, row, col);
elm = DoOperation3Args(ElmMatOper, mat, row, col);
if (elm == 0) {
ErrorMayQuit("Matrix access method must return a value", 0, 0);
}
Expand Down Expand Up @@ -840,6 +848,9 @@ void ASS_MAT(Obj mat, Obj row, Obj col, Obj obj)
Obj rowlist = ELM_PLIST(mat, r);
Int c = INT_INTOBJ(col);

if (!rowlist)
ErrorMayQuit("Matrix Assignment: <mat>[%d] must have an assigned value",
(Int)r, (Int)c);
ASS_LIST(rowlist, c, obj);
return;
}
Expand Down
45 changes: 36 additions & 9 deletions tst/testinstall/listindex.tst
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Original file line number Diff line number Diff line change
Expand Up @@ -324,21 +324,48 @@ Error, no method found! For debugging hints type ?Recovery from NoMethodFound
Error, no 1st choice method found for `[]:=' on 3 arguments

# Indexing into plain lists
gap> l := [[]];;
gap> l[1,2] := 4;
gap> l := [,[,4]];
[ , [ , 4 ] ]
gap> l[0,1]; # row is out of bounds
Error, no method found! For debugging hints type ?Recovery from NoMethodFound
Error, no 1st choice method found for `MatElm' on 3 arguments
gap> l[1,1]; # row is in bounds but missing
Error, Matrix Element: <mat>[1] must have an assigned value
gap> l[2,1]; # row is there but entry is missing
Error, Matrix Element: <mat>[2,1] must have an assigned value
gap> l[3,1]; # row is out of bounds
Error, no method found! For debugging hints type ?Recovery from NoMethodFound
Error, no 1st choice method found for `MatElm' on 3 arguments
gap> l[2,0]; # column is out of bounds
Error, no method found! For debugging hints type ?Recovery from NoMethodFound
Error, no 1st choice method found for `MatElm' on 3 arguments
gap> l[2,2]; # OK
4
gap> l[2,3]; # column is out of bounds
Error, List Element: <list>[3] must have an assigned value
gap> l[2,2] := 4;
4
gap> l;
[ [ , 4 ] ]
gap> l[1,1] := 3;;
[ , [ , 4 ] ]
gap> l[0,1] := 3; # error, row out of bounds
Error, no method found! For debugging hints type ?Recovery from NoMethodFound
Error, no 1st choice method found for `SetMatElm' on 4 arguments
gap> l[1,1] := 3; # error, row is missing
Error, Matrix Assignment: <mat>[1] must have an assigned value
gap> l[2,1] := 3; # OK
3
gap> l[3,1] := 3; # error, row out of bounds
Error, no method found! For debugging hints type ?Recovery from NoMethodFound
Error, no 1st choice method found for `SetMatElm' on 4 arguments
gap> l;
[ [ 3, 4 ] ]
[ , [ 3, 4 ] ]
gap> l[2,1];
Error, List Element: <list>[2] must have an assigned value
gap> MakeImmutable(l[1]);;
gap> l[1,1] := 2;;
3
gap> MakeImmutable(l[2]);;
gap> l[2,1] := 2;;
Error, List Assignment: <list> must be a mutable list
gap> l;
[ [ 3, 4 ] ]
[ , [ 3, 4 ] ]

# that's all, folks
gap> STOP_TEST( "listindex.tst", 1);