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mod_vhost_alias: reserve a byte for the terminating NUL in checkspace #833

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mod_vhost_alias: reserve a byte for the terminating NUL in checkspace #833

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4 changes: 4 additions & 0 deletions changes-entries/vhost-alias-interpolate-nul.txt
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Original file line number Diff line number Diff line change
@@ -0,0 +1,4 @@
*) mod_vhost_alias: Reserve a byte for the terminating NUL when
interpolating VirtualDocumentRoot/VirtualScriptAlias, so a name of
a length that fills the buffer exactly cannot write one byte past
it. [arshiya tabasum]
5 changes: 4 additions & 1 deletion modules/mappers/mod_vhost_alias.c
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Original file line number Diff line number Diff line change
Expand Up @@ -244,7 +244,10 @@ static APR_INLINE int vhost_alias_checkspace(request_rec *r, char *buf,
"VirtualDocumentRoot expansion too large");
return HTTP_REQUEST_URI_TOO_LARGE;
}
if (*pdest + size > buf + HUGE_STRING_LEN) {
/* Reserve one byte for the terminating NUL: dest must never reach
* buf + HUGE_STRING_LEN, or the '\0' written here and at the end of
* vhost_alias_interpolate() lands one byte past the buffer. */
if (*pdest + size >= buf + HUGE_STRING_LEN) {
**pdest = '\0';
if (r->filename) {
r->filename = apr_pstrcat(r->pool, r->filename, buf, NULL);
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