Skip to content

aCalc: fix off-by-two in INC() runtime stack-overflow guard #40

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
physwkim wants to merge 1 commit into
base: master
Choose a base branch
from
Open

aCalc: fix off-by-two in INC() runtime stack-overflow guard #40

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
2 changes: 1 addition & 1 deletion calcApp/src/aCalcPerform.c
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -86,7 +86,7 @@ int aCalcStackLW = 0; /* low-water mark */
++ps; \
if ((int)((ps)-top) > aCalcStackHW) \
aCalcStackHW = (int)((ps)-top); \
if ((ps-top)>ACALC_STACKSIZE) { \
if ((ps-top)>ACALC_STACKSIZE-2) { \
printf("aCalcPerform:stack overflow\n"); \
freeStack(flp, stack); return(-1); \
} else { \
Expand Down
38 changes: 37 additions & 1 deletion tests/acalcTest.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -92,6 +92,32 @@ static void testAValExpr(const char* expr, double* args, double** aargs, double*
//free(rpn);
}

/* Assert whether an expression the postfix compiler accepts overflows the
* runtime value stack. Operators such as NDERIV/DERIV/FITPOLY push scratch
* elements at run time that the compiler's per-opcode stack accounting does
* not model, so a deep-enough expression passes aCalcPostfix() yet drives the
* runtime stack past its end. The INC() guard must reject it (aCalcPerform
* returns non-zero) instead of writing out of bounds. */
static void testStackOverflow(const char* expr, double* args, double** aargs, bool expectOverflow)
{
unsigned char rpn[255];
short err;

double val = 0.0;
double aval[12] = {0.0};
epicsUInt32 amask;

if (aCalcPostfix(expr, rpn, &err))
{
testOk(false, "postfix rejected '%s': %s", expr, aCalcErrorStr(err));
return;
}

bool overflow = (aCalcPerform(args, 12, aargs, 12, 12, &val, aval, rpn, 1, &amask) != 0);
testOk(overflow == expectOverflow, "%s -> %s", expr,
overflow ? "runtime stack overflow rejected" : "evaluated");
}


MAIN(acalcTest)
{
Expand Down Expand Up @@ -125,7 +151,7 @@ MAIN(acalcTest)
double* aargs[12] = {AA, BB, CC, DD, EE, FF, GG, HH, II, JJ, KK, LL};


testPlan(148);
testPlan(150);

testValExpr("finite(1)", args, aargs, 1);
testValExpr("finite(AA)", args, aargs, 1);
Expand Down Expand Up @@ -353,6 +379,16 @@ MAIN(acalcTest)
/* Reset B */
args[1] = B;

/* Runtime value-stack overflow guard (INC off-by-two). NDERIV pushes
* three scratch elements the compiler does not account for; 15 levels of
* nesting evaluate, 16 must be rejected by the runtime guard rather than
* writing past stack[ACALC_STACKSIZE-1]. Without the fix the k=16 case
* writes out of bounds and crashes the test binary. */
testStackOverflow("1+(1+(1+(1+(1+(1+(1+(1+(1+(1+(1+(1+(1+(1+(1+(NDERIV(AA,2))))))))))))))))",
args, aargs, false);
testStackOverflow("1+(1+(1+(1+(1+(1+(1+(1+(1+(1+(1+(1+(1+(1+(1+(1+(NDERIV(AA,2)))))))))))))))))",
args, aargs, true);

/* Parse error tests */
{
unsigned char rpn[255];
Expand Down