[UNIX] Linux procfs Information Disclosure

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Linux procfs Information Disclosure
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SUMMARY

"The process file system, or procfs, implements a view of the system
process table inside the file system. It is normally mounted on /proc,
and is required for the complete operation of programs such as ps(1) and
w(1)."

The Linus kernel procfs code does not validate its user provided
variables, allowing local attackers to retrieve sensitive information from
memory such as the root's password.

DETAILS

Vulnerable Systems:
* Linux version 2.6.14.4 and prior

The /proc file system (procfs) is a special file system in the Linux
kernel. It's a virtual file system: it is not associated with a block
device but exists only in memory. The files in the procfs are there to
allow users' programs access to certain information from the kernel (like
process information in /proc/[0-9]+/), but also for debug purposes (like
/proc/ksyms).

The function proc_calc_metrics does not properly validate variables,
allowing attackers enter restricted memory and obtaining information that
could not be gathered otherwise.

Vulnerable Code:
fs/proc/proc_misc.c:
static int proc_calc_metrics(char *page, char **start, off_t off,
int count, int *eof, int len)
{
if (len <= off+count) *eof = 1;
*start = page + off;
len -= off;
if (len>count) len = count;
if (len<0) len = 0;
return len;
}

In the above code we can see that the values of 'off' and 'count' are not
checked to see if they contain negative number.

An attacker can place a negative number, pointing the 'start' variable to
a memory that may contain sensitive information.


ADDITIONAL INFORMATION

The information has been provided by <mailto:karl@xxxxxxxxxxxxxxxxxxxx>
Karl Janmar.



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