Strings and Integers - Revision history

Thomas Herlea: Added navigation to facilitate sequential reading online

2010-09-09T16:49:16Z

Added navigation to facilitate sequential reading online

KirstenS: /* Off by One Error */

2009-02-11T02:06:25Z

‎Off by One Error

KirstenS: /* String Termination Errors */

2009-02-11T02:06:16Z

‎String Termination Errors

KirstenS: /* Common String Errors */

2009-01-29T01:30:59Z

‎Common String Errors

KirstenS: /* Integer Conversion */

2009-01-15T16:11:09Z

‎Integer Conversion

KirstenS: /* Integer conversion */

2009-01-15T16:10:53Z

‎Integer conversion

KirstenS: /* Integer Overflows */

2009-01-15T16:10:15Z

‎Integer Overflows

KirstenS: /* Off by One Error */

2009-01-13T19:54:47Z

‎Off by One Error

KirstenS: /* String Termination Errors */

2009-01-13T19:54:34Z

‎String Termination Errors

KirstenS: /* Common String Errors */

2009-01-13T19:53:50Z

‎Common String Errors

@@ Line 1: / Line 1: @@
-[[OWASP Code Review Guide Table of Contents]]__TOC__
+{{LinkBar
 ==Introduction:==
 Strings are not a defined Type in C or C++, but simply a contiguous array of characters terminated by a null (\0) character. The length of the string is the amount of characters which precede the null character. C++ does contain template classes which address this feature of the programming language:  '''std::basic_string''' and '''std::string''' These classes address some security issues but not all.
@@ Line 88: / Line 94: @@
 ''Here y would have the value of 65533 due to the loopback effect of the conversion from signed to unsigned.''
 [[Category:OWASP Code Review Project]]

← Older revision		Revision as of 02:06, 11 February 2009
Line 52:		Line 52:

	Off-by-one errors are common to looping functionality, wherein a looping functionality is performed on an object in order to manipulate the contents of an object such as copy or add information. The off-by-one error is a result of an error on the loop counting functionality.		Off-by-one errors are common to looping functionality, wherein a looping functionality is performed on an object in order to manipulate the contents of an object such as copy or add information. The off-by-one error is a result of an error on the loop counting functionality.
−

	for (i = 0; i < 5; i++) {		for (i = 0; i < 5; i++) {

@@ Line 41: / Line 41: @@
    strncpy(c, a, sizeof(c));
+  }
 Verify that the following are used:

@@ Line 9: / Line 9: @@
 Common issues include:
-#Input validation errors
+# Input validation errors
-#Unbounded Errors
+# Unbounded errors
-#Truncation issues
+# Truncation issues
-#Out-of-bounds writes
+# Out-of-bounds writes
-#String Termination Errors
+# String Termination errors
-#Off-by-one errors`
+# Off-by-one errors
 Some of the issues mentioned above have been covered in the [[Reviewing Code for Buffer Overruns and Overflows]] section in this guide.
@@ Line 21: / Line 21: @@
 ====String Copies====
-Occur when data is copied from a unbounded source to a fixed length character array
+Unbounded errors occur when data is copied from a unbounded source to a fixed length character array.
   void main(void) {
@@ Line 31: / Line 31: @@
 ====String Termination Errors====
-Failure to properly terminate strings with a null can result in system failure
+Failure to properly terminate strings with a null can result in system failure.
   int main(int argc, char* argv[]) {
@@ Line 50: / Line 50: @@
 ====Off by One Error====
-(Looping through arrays should be looped in a n-1 manner, as we must remember arrays and vectors start as 0. This is not specific to C/C++, but Java and C# also.)
+Looping through arrays should be looped in a n-1 manner, as we must remember arrays and vectors start as 0. This is not specific to C/C++, but Java and C# also.)
 Off-by-one errors are common to looping functionality, wherein a looping functionality is performed on an object in order to manipulate the contents of an object such as copy or add information. The off-by-one error is a result of an error on the loop counting functionality.

@@ Line 88: / Line 88: @@
   unsigned short y;
   y = x;
- ''Here y would have the value of 65533 due to the loopback effect of the conversion from signed to unsigned.''
 [[Category:OWASP Code Review Project]]

@@ Line 82: / Line 82: @@
 Also, here we can see the result of an unsigned int being incremented, which loops the integer back to the value 0. As before, this should also be examined to see if there are any compensating controls to prevent this from happening.
-====Integer conversion====
+====Integer Conversion====
 When converting from a signed to an unsigned integer, care must also be taken to prevent a representation error.

@@ Line 66: / Line 66: @@
 ===Issues with Integers===
 ====Integer Overflows====
-When an integer is increased beyond its maximum range or decreased below its minimum value, overflows occur. Overflows can be signed or unsigned. Signed when the overflow carries over to the sign bit,unsigned when the value being intended to be represented is no longer represented correctly.
+When an integer is increased beyond its maximum range or decreased below its minimum value, overflows occur. Overflows can be signed or unsigned. Signed when the overflow carries over to the sign bit, unsigned when the value being intended to be represented is no longer represented correctly.
   int x;
@@ Line 80: / Line 80: @@
   ''Here y would have a value of 0 after the increment''
 Also, here we can see the result of an unsigned int being incremented, which loops the integer back to the value 0. As before, this should also be examined to see if there are any compensating controls to prevent this from happening.
 ====Integer conversion====

@@ Line 49: / Line 49: @@
   fgets() instead of gets()
-===Off by One Error===
+====Off by One Error====
 (Looping through arrays should be looped in a n-1 manner, as we must remember arrays and vectors start as 0. This is not specific to C/C++, but Java and C# also.)
@@ Line 62: / Line 62: @@
 If the condition was set such that i<=5 (less than or equal to 5), the loop won’t terminate until i reaches 6, which may not be what is intended.
 Also, counting from 1 instead of 0 can cause similar issues, as there would be one less iteration. Both of these issues relate to an off-by-one error where the loop either under or over counts.
 ===Issues with Integers===

@@ Line 6: / Line 6: @@
 ==Common String Errors==
-Common string errors can be related to mistakes in implementation which may cause drastic security and availability issues.
+Common string errors can be related to mistakes in implementation, which may cause drastic security and availability issues. C/C++ do not have the comfort other programming languages provide, such as Java and C# .NET, relating to buffer overflows and such due to a String Type not being defined.
 Common issues include:
@@ Line 31: / Line 30: @@
+   }
-====String Termination Errors====
+===String Termination Errors===
 Failure to properly terminate strings with a null can result in system failure
@@ Line 44: / Line 43: @@
-It is recommended that it should be verified that the following is used:
+Verify that the following are used:
   strncpy() instead of strcpy()
   snprintf() instead of sprintf()
@@ Line 50: / Line 50: @@
-====Off by one error====
+===Off by One Error===
-(Looping through arrays should be looped in a n-1 manner as we must remember arrays and vectors start as 0. This is not specific to C/C++ but Java and C# also.)
+(Looping through arrays should be looped in a n-1 manner, as we must remember arrays and vectors start as 0. This is not specific to C/C++, but Java and C# also.)
   for (i = 0; i < 5; i++) {
      /* Do Stuff */
+  }
-Here i starts with a value of 0, it then increments to 1, then 2,3 & 4. When i reaches 5 then the condition i<5 is false and the loop terminates.
+Here i starts with a value of 0, it then increments to 1, then 2, 3 & 4. When i reaches 5 then the condition i<5 is false and the loop terminates.
-If the condition was set such that i<=5 (less than or equal to 5) the loop wont terminate until i reaches 6 which may not be what is intended.
+If the condition was set such that i<=5 (less than or equal to 5), the loop won’t terminate until i reaches 6, which may not be what is intended.
-Also counting from 1 instead of 0 can cause similar issues as there would be one less iterations. Both of these issues relate to a off-by-one error where the loop either under or over counts.
+Also, counting from 1 instead of 0 can cause similar issues, as there would be one less iteration. Both of these issues relate to an off-by-one error where the loop either under or over counts.
 ===Issues with Integers===
 ====Integer Overflows====
-When an integer is increased beyond its maximum range or decreased below its minimum value overflows occur.
+When an integer is increased beyond its maximum range or decreased below its minimum value, overflows occur. Overflows can be signed or unsigned. Signed when the overflow carries over to the sign bit,unsigned when the value being intended to be represented is no longer represented correctly.
   int x;
@@ Line 75: / Line 74: @@
   ''Here x would have the value of -2,147,483,648 after the increment''
-It is important when reviewing the code that some measure should be implemented such that the overflow does not occur. This is not the same as relying on the value "never going to reach this value (2,147,483,647)".
+It is important when reviewing the code that some measure should be implemented such that the overflow does not occur. This is not the same as relying on the value "never going to reach this value (2,147,483,647)". This may be done by some supporting logic or a post increment check.
   unsigned int y;
@@ Line 83: / Line 81: @@
   ''Here y would have a value of 0 after the increment''
-Also here we can see the result of an unsigned int being incremented which loops the integer back to the value 0
+Also, here we can see the result of an unsigned int being incremented, which loops the integer back to the value 0. As before, this should also be examined to see if there are any compensating controls to prevent this from happening.
 ====Integer conversion====
-When converting from a signed to an unsigned integer care must also be taken to prevent a representation error.
+When converting from a signed to an unsigned integer, care must also be taken to prevent a representation error.
   int x = -3;
@@ Line 93: / Line 90: @@
   y = x;
   ''Here y would have the value of 65533 due to the loopback effect of the conversion from signed to unsigned.''
 [[Category:OWASP Code Review Project]]