Bug #61020 [Opn]: Security risk from find usage recommendation

Edit report at https://bugs.php.net/bug.php?id=61020&edit=1 ID: 61020 User updated by: ondrej@php.net Reported by: ondrej@php.net Summary: Security risk from find usage recommendation Status: Open Type: Bug Package: *Configuration Issues PHP Version: 5.4.0RC7 Block user comment: N Private report: N New Comment: s/most error-prone/least error-prone/ Previous Comments: ------------------------------------------------------------------------ [2012-02-09 00:31:44] ondrej@php.net And if you cannot use find with -delete or -execdir at least do: find /path/to/sessions -mindepth 1 -maxdepth 1 -cmin +24 -execdir rm "{}" \; ------------------------------------------------------------------------ [2012-02-09 00:29:10] ondrej@php.net Description: ------------ ; NOTE: If you are using the subdirectory option for storing session files [...] ; find /path/to/sessions -cmin +24 | xargs rm because it is prone to '\n' attack. You can see the security considerations of GNU find. Much better would be: find /path/to/sessions -cmin +24 -delete or at least find /path/to/sessions -cmin +24 -execdir rm "{}" \; (GNU find) The most error-prone way is something we cooked up in Debian: find /var/lib/php5/ -depth -mindepth 1 -maxdepth 1 -type f -ignore_readdir_race -cmin +24 ! -execdir fuser -s {} 2>/dev/null \; -delete which depends on fuser at least version 22.15 (which has removed fork() call which was able to swamp up whole system with zombies). The fuser call checks if the session file is still in use, because the script was deleting still active sessions opened 24+ mins ago. Test script: --------------- Race condition for -exec rm {} \;: while true; do mkdir /var/lib/php5/blah touch /var/lib/php5/blah/passwd rmdir /var/lib/php5/blah ln -s /etc /var/lib/php5/blah done xargs attack: ondrej@howl:/tmp/php_sess$ touch bar ondrej@howl:/tmp/php_sess$ touch -t 201201010000 "$(echo -e 'foo\nbar')" ondrej@howl:/tmp/php_sess$ ls -l total 0 -rw-r--r-- 1 ondrej ondrej 0 Feb 9 01:26 bar -rw-r--r-- 1 ondrej ondrej 0 Jan 1 00:00 foo?bar ondrej@howl:/tmp/php_sess$ find /tmp/php_sess -mmin +24 /tmp/php_sess/foo?bar ondrej@howl:/tmp/php_sess$ find /tmp/php_sess -mmin +24 | xargs rm rm: cannot remove `/tmp/php_sess/foo': No such file or directory ondrej@howl:/tmp/php_sess$ ls -l total 0 -rw-r--r-- 1 ondrej ondrej 0 Jan 1 00:00 foo?bar ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=61020&edit=1