Problem - Kevin Tafuro

(see Recipe 3.2). The format-string protection also requires access to the frame
pointer because it attempts to filter out arguments that are not pointers into the heap
or the local variables on the stack.
See Also
• MSDN reference for strsafe.h: http://msdn.microsoft.com/library/en-us/winui/
winui/windowsuserinterface/resources/strings/usingstrsafefunctions.asp
• SafeStr from Zork: http://www.zork.org/safestr/
• StackGuard from Immunix: http://www.immunix.org/stackguard.html
• ProPolice from IBM: http://www.trl.ibm.com/projects/security/ssp/
• LibSafe from Avaya Labs: http://www.research.avayalabs/project/libsafe/
• Netstrings by Dan J. Bernstein: http://cr.yp.to/proto/netstrings.txt
• Recipes 3.2, 3.4
3.4 Using the SafeStr Library
Problem
You want an alternative to using the standard C string-manipulation functions to
help avoid buffer overflows (see Recipe 3.3), format-string problems (see Recipe 3.2),
and the use of unchecked external input.
Solution
Use the SafeStr library, which is available from http://www.zork.org/safestr/.
Discussion
The SafeStr library provides an implementation of dynamically sizable strings in C.
In addition, the library also performs reference counting and accounting of the allocated
and actual sizes of each string. Any attempt to increase the actual size of a
string beyond its allocated size causes the library to increase the allocated size of the
string to a size at least as large. Because strings managed by SafeStr (“safe strings”)
are dynamically sized, safe strings are not a source of potential buffer overflows. (See
Recipe 3.3.)
Safe strings use the type safestr_t, which can actually be cast to the normal C-style
string type, char *, though we strongly recommend against doing so where it can be
avoided. In fact, the only time you should ever cast a safe string to a normal C-style
string is for read-only purposes. This is also the only reason why the safestr_t type
was designed in a way that allows casting to normal C-style strings.
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