Edit report at https://bugs.php.net/bug.php?id=61020&edit=1
ID: 61020
User updated by: ond...@php.net
Reported by: ond...@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:
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 "{}" \;
Previous Comments:
------------------------------------------------------------------------
[2012-02-09 00:29:10] ond...@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
------------------------------------------------------------------------
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Edit this bug report at https://bugs.php.net/bug.php?id=61020&edit=1
