CVE-2016-4913: Infoleak

First published: Thu May 19 2016(Updated: )

A vulnerability was found in the Linux kernel. Payloads of NM entries are not supposed to contain NUL. When such entry is processed, only the part prior to the first NUL goes into the concatenation (i.e. the directory entry name being encoded by a bunch of NM entries). The process stops when the amount collected so far + the claimed amount in the current NM entry exceed 254. However, the value returned as the total length is the sum of *claimed* sizes, not the actual amount collected. And that can grow pretty large - not unlimited, since you'd need to put CE entries in between to be able to get more than the maximum that could be contained in one isofs directory entry / continuation chunk and the process stops once it had encountered 32 CEs, but you can get about 8Kb easily. And that's what will be passed to readdir callback as the name length. 8Kb __copy_to_user() from a buffer allocated by __get_free_page() References, CVE-ID request and response: <a href="http://seclists.org/oss-sec/2016/q2/363">http://seclists.org/oss-sec/2016/q2/363</a> <a href="http://seclists.org/oss-sec/2016/q2/365">http://seclists.org/oss-sec/2016/q2/365</a> Upstream fix: <a href="https://git.kernel.org/linus/99d825822eade8d827a1817357cbf3f889a552d6">https://git.kernel.org/linus/99d825822eade8d827a1817357cbf3f889a552d6</a>

Credit: security@debian.org security@debian.org security@debian.org

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