Time-of-check to time-of-use: Difference between revisions

Revision as of 22:58, 13 February 2007

Revision as of 16:32, 13 March 2008

Line 6:

In [[Unix]], the following [[C (programming language)|C]] code, when used in a [[setuid]] program, is a TOCTTOU bug:

<source lang="c">

if (access(file, R_OK) != 0) {

exit(1);

}

iffd (access= open(file, R_OKO_RDONLY) != 0) {;

// do something with fd...

exit(1);

</source>

}

fd = open(file, O_RDONLY);

// do something with fd...

Here, ''access'' is intended to check whether the real user who executed the setuid program would normally be allowed to read the file (i.e., ''access'' checks the [[real userid]] rather than [[effective userid]]).