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#1685 TclEvalObjvInternal: potential segfault

obsolete: 8.4a4
closed-invalid
Vince Darley
45. Parsing and Eval (224)
9
2002-06-26
2001-11-21
Don Porter
No

Within TclEvalObjvInternal(), trace
procedures are called in a loop like:

for (tracePtr = iPtr->tracePtr;
tracePtr != NULL;
tracePtr = nextPtr) {
nextPtr = tracePtr->nextPtr;
...
(*tracePtr->proc)(tracePtr->clientData, interp,
iPtr->numLevels, commandCopy,
cmdPtr->proc, cmdPtr->clientData,
objc, argv);
}

Trouble with that is (*tracePtr->proc) could
do anything, including calling Tcl_DeleteTrace
on the Tcl_Trace held by nextPtr. If it does
that, there will be a segfault.

The technique used by command and variable traces
that involves defining additional structures
such as ActiveCommandTrace and special handling
could be adapted to solve this problem.

Discussion

  • Don Porter

    Don Porter - 2001-11-26

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    The TIP 62 reference implementation
    (Tcl Patch 562580) appears to address
    this potential bug, though it's a
    patch against an earlier HEAD.

     

  • Don Porter

    Don Porter - 2002-06-21
    • priority: 5 --> 9
     

  • Don Porter

    Don Porter - 2002-06-21

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    Can we check that TIP 62 really fixed this?

     

  • miguel sofer

    miguel sofer - 2002-06-21

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    It looks like it did; that logic now moved from TEOVI to
    TclCheck[...]Traces in tclCmdMZ.c, a cursory look (without
    deep understanding) suggests the issue is handled there.

    Assigning to Vince so that he (hopefully) confirms that
    all's well and closes the ticket.

     

  • miguel sofer

    miguel sofer - 2002-06-21
    • assigned_to: msofer --> vincentdarley
     

  • Vince Darley

    Vince Darley - 2002-06-26

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    I agree with Miguel. It looks as if there is not a
    problem. I also recall doing extensive testing of this
    sort of thing (trace deletes trace, trace deletes cmd, etc),
    with no adverse effects.

     

  • Vince Darley

    Vince Darley - 2002-06-26
    • status: open --> closed-invalid