[PHP-INTERNALS] basename() memory access violation

On June 14, 2004 01:51 pm, Alexander Valyalkin wrote:
Here is patch for basename() function, which prevents possible
memory access violation:

=========cut=========
--- string.c Thu May 13 20:44:32 2004
+++ string_basename.c Mon Jun 14 20:43:33 2004
@@ -1079,9 +1079,9 @@


/* strip trailing slashes */
- while (*c == '/'
+ while (c >= s && *c == '/'
#ifdef PHP_WIN32
- || (*c == '\\' && !IsDBCSLeadByte(*(c-1)))
+ || (c > s && *c == '\\' && !IsDBCSLeadByte(*(c-1)))
#endif
)
c--;
@@ -1092,10 +1092,10 @@
}

#ifdef PHP_WIN32
- if ((c = strrchr(s, '/')) || ((c = strrchr(s, '\\')) &&
!IsDBCSLeadByte(*(c-1)))) {
+ if ((c = strrchr(s, '/')) || ((c = strrchr(s, '\\')) && c > s &&
!IsDBCSLeadByte(*(c-1)))) {
if (*c == '/') {
char *c2 = strrchr(s, '\\');
- if (c2 && !IsDBCSLeadByte(*(c2-1)) && c2 > c) {
+ if (c2 && c2 > s && !IsDBCSLeadByte(*(c2-1)) && c2 > c) {
c = c2;
}
}
=========cut==========

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Ilia Alshanetsky wrote:
Do you have an example script that can be used to reproduce the supposed
memory access violation?

At 10:30 PM 6/14/2004 +0200, Christian Schneider wrote:
Ilia Alshanetsky wrote:
The function php_basename actually DOES access the char at s-1, i.e. one
byte before the string it is passed. If you hand it a buffer gotten from
malloc you get a valgrind hit. If I use emalloc this doesn't happen, I
guess emalloc has some header stuff before the allocation. If for whatever
reason s[-1] contains '/' then things would get even worse.

Conclusion: The internal function php_basename IS accessing one byte
before the buffer passed to it but the PHP environment seems to hide this
behaviour.
Is this a bug which should proactively been fixed? Or do we rely on the
environment to guarantee that we can access s[-1] without problems? I
don't know and it's up to you PHP gods to decide ;-)

- Chris

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