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Multiple Vendor profil(2) Vulnerability
Some *BSD's use a profil(2) system call that dates back to "version 6" unix. This system call arranges for the kernel to sample the PC and increment an element of an array on every profile clock tick. The security issue stems from the fact that profiling is not turned off when a process execve(2)'s another program image. As the size and location of this array as well as the scale factor are under the program's control, it is possible to arrange for an arbitrary 16-bit program virtual address to be incremented on each profile clock tick. Although unlikely, it is theoretically possible that an attacker with local access and knowledge of the addresses used by privileged programs could construct an exploit. It may be that there are no candidate addresses that, when incremented, result in a security failure. However, as this can turn -1 into 0, and 0 into 1, and as security-related system calls and library functions often return either -1 or 0, this mechanism could turn system call returns of success into failure or failure into success if a program stores system call results into memory locations. |
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