Thread: Warning C6386: Buffer Overrun While Writing To 'p->op'

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1. December 2nd, 2015, 03:14 PM #1 pebmeister
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   warning C6386: Buffer overrun while writing to 'p->op'

   Hello I am using Visual Studio 2015 and ran Code Analysis on my solution It gives me this warning 1> Warning C6386 Buffer overrun while writing to 'p->op': the writable size is 'size' bytes, but '8' bytes might be written. pasm64-2015 c:\users\paul\desktop\paul_paul-pc_2148\pasm64\node.c 274 the line in question is p->op[i] = va_arg(ap, parseNodePtr); I don't see anything wrong with my code. I allocate nops * sizeof(parseNodePtr) bytes and iterate 1 to nops in my loop I also don't wan to use Code: #pragma warning(disable:6385) #pragma warning(disable:6386) This code is from an assembler that I wrote. The code runs perfectly on Windows, Linux, and MaC. I would like my code not to have any warnings (including Code Analysis) without using a bandaid. Any ideas? Code: /// <summary> /// create Operator parseNode /// </summary> /// <param name="oper">The operator.</param> /// <param name="nops">The number of operators.</param> /// <param name="">The operators.</param> /// <returns>parseNodePtr.</returns> parseNodePtr opr(int oper, int nops, ...) { va_list ap; int i = 0; size_t size = 0; const char* module = "opr"; /* allocate node */ parseNodePtr p = AllocateNode(); if (p == NULL) { FatalError(module, ErrorOutofMemory); return NULL; } size = nops * sizeof(parseNodePtr); if ((p->op = (parseNodePtr*) malloc(size)) == NULL) { FatalError(module, ErrorOutofMemory); return NULL; } /* copy information */ p->type = typeOpr; p->opr.oper = oper; p->nops = nops; va_start(ap, nops); for (i = 0; i < nops; i++) p->op[i] = va_arg(ap, parseNodePtr); va_end(ap); return p; }

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2. December 2nd, 2015, 03:20 PM #2 pebmeister
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   Re: warning C6386: Buffer overrun while writing to 'p->op'

   FYI here is the parseNode data type Code: typedef struct { int value; /* value of constant */ int IsPC; /* TRUE is value is PC */ } conParseNode; typedef struct { char* value; /* value of string */ char* allocated; /* allocated string */ int len; } strParseNode; /* identifiers */ typedef struct { char* name; SymbolTablePtr i; /* symbol entry */ } idParseNode; /* operators */ typedef struct { int oper; /* operator */ } oprParseNode; /* opcodes */ typedef struct { int instruction; /* untranslated instruction */ int opcode; /* opcode */ int mode; /* mode */ int pc; /* program counter */ } opParseNode; /* macro execution node */ typedef struct { void* macro; void* macroParams; } macParseNode; /* data definition node */ typedef struct { int size; /* 1 = byte 2 = word, 0 = string */ void* data; } dataParseNode; /* nodes union */ typedef struct parseNode { nodeEnum type; /* type of node */ union { conParseNode con; /* constants */ idParseNode id; /* identifiers */ oprParseNode opr; /* operators */ opParseNode opcode; /* opcodes */ macParseNode macro; /* macro execution */ dataParseNode data; /* numeric data node */ strParseNode str; /* string node */ }; int nops; /* number of operands */ struct parseNode **op; /* operands */ struct parseNode* next; /* next node in tree */ struct parseNode* prev; /* previous node */ } parseNode, *parseNodePtr;

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3. December 3rd, 2015, 03:21 AM #3 superbonzo
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   Re: warning C6386: Buffer overrun while writing to 'p->op'

   as far as I can tell, I see three problems: 1-if nops is negative you may end up allocating a lot of unused memory 2-if nops is zero it may cause a "FatalError" or maybe not, it's implementation defined 3-if the nops * sizeof product overflows you may end up with a buffer overrun indeed ( on a 32bit system, take nops = 2^30, you'll have a zero 'size' malloc (see point 2) ) maybe, the code analisys tool is complaining about point 3 ...

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4. December 3rd, 2015, 09:59 AM #4 pebmeister
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   Re: warning C6386: Buffer overrun while writing to 'p->op'

   Thanks for the response. I can now see how it could be a buffer overrun. In the practical world nops will always be 0,1 or 2 I should special case 0. I will also do a range check on nops the entry.

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5. December 3rd, 2015, 10:52 AM #5 pebmeister
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   Re: warning C6386: Buffer overrun while writing to 'p->op'

   Wow found the real problem [code] size = nops * sizeof(parseNodePtr); [code] should be [code] size = nops * sizeof(parseNode); [code]

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6. December 4th, 2015, 03:11 AM #6 superbonzo
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   Re: warning C6386: Buffer overrun while writing to 'p->op'

   Originally Posted by pebmeister Wow found the real problem I doubt so, unless your real intent was to allocate memory for nops parseNode's for constructing nops parseNode pointers ... does not make much sense to me

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7. December 4th, 2015, 10:23 AM #7 pebmeister
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   Re: warning C6386: Buffer overrun while writing to 'p->op'

   I changed it slightly and now I get no warnings. Code: /// <summary> /// create Operator parnode /// </summary> /// <param name="oper">The operator.</param> /// <param name="nops">The number of ops.</param> /// <param name="">The .</param> /// <returns>parseNodePtr.</returns> parseNodePtr opr(int oper, int nops, ...) { va_list ap; int i = 0; const char* module = "opr"; /* allocate node */ parseNodePtr p = AllocateNode(); if (p == NULL) { FatalError(module, ErrorOutofMemory); return NULL; } /* copy information */ p->type = typeOpr; p->opr.oper = oper; if (nops < 0 || nops >= MAX_OPS) { FatalError(module, ErrorValueOutofRange); return NULL; } p->nops = nops; if (nops > 0 && nops < MAX_OPS) { p->op = (parseNodePtr*) malloc(sizeof(parseNodePtr) * nops); if ((p->op) == NULL) { FatalError(module, ErrorOutofMemory); return NULL; } va_start(ap, nops); for (i = 0; i < nops; i++) p->op[i] = va_arg(ap, parseNodePtr); va_end(ap); } return p; }

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