CVE-2010-3848: Buffer Overflow

Description of problem: Reported by Nelson Elhage.

CVE-2010-3848 AFECONET kernel stack overflow CVE-2010-3849 AFECONET saddr->cookie NULL dereferences CVE-2010-3850 AFECONET SIOCSIFADDR ioctl does not check privileges

The two main vulnerabilities lie in the econetsendmsg() function. If CONFIGECONETAUNUDP, the function declares a variable-length array of iovec's on the stack:

static int econetsendmsg(struct kiocb iocb, struct socket sock, struct msghdr msg, sizet len) { ... #ifdef CONFIGECONETAUNUDP ... struct iovec iov[msg->msgiovlen+1]; ... #endif

"msg->msgiovlen" is a user-controlled value <= 1024; 1024 'struct iovec's is enough to overflow the kernel stack and clobber the 'threadinfo' struct on either 32- or 64-bit systems with or without CONFIG4KSTACKS.

The code populates 'iov' with user-controlled values, so this is almost certainly exploitable for privesc.

The second bug is conveniently labeled as such for anyone who cares to look:

/ BUG: saddr may be NULL / eb->cookie = saddr->cookie;

In fact, 'saddr' comes from userspace and may be NULL (if non-NULL, it will have been copied to kernelspace), leading to a NULL-pointer dereference. This saddr->cookie dereference appears twice, once in the "hardware" case and once in the "UDP emulation" case. This is easily exploitable for an oops, but probably not anything more.

The final issue is in the ecdevioctl function. The SIOCSIFADDR ioctl does not check privileges, allowing an unprivileged user to assign econet addresses to arbitrary interfaces. It is possible this is intentional, but AFAIK it would be unusual for SIOCSIFADDR to be unprivileged, so this may be an accident.

Note that it is necessary to use this property in order to make the first two bugs exploitable, since econetsendmsg will return almost immediately if no econet addresses are configured.

Reference: http://seclists.org/oss-sec/2010/q4/236