Commit b469da14 authored by Committed by Matthieu Herrb
Fixed off-by-one writes (CVE-2018-14599).
The functions XGetFontPath, XListExtensions, and XListFonts are vulnerable to an off-by-one override on malicious server responses. The server replies consist of chunks consisting of a length byte followed by actual string, which is not NUL-terminated. While parsing the response, the length byte is overridden with '\0', thus the memory area can be used as storage of C strings later on. To be able to NUL-terminate the last string, the buffer is reserved with an additional byte of space. For a boundary check, the variable chend (end of ch) was introduced, pointing at the end of the buffer which ch initially points to. Unfortunately there is a difference in handling "the end of ch". While chend points at the first byte that must not be written to, the for-loop uses chend as the last byte that can be written to. Therefore, an off-by-one can occur. I have refactored the code so chend actually points to the last byte that can be written to without an out of boundary access. As it is not possible to achieve "ch + length < chend" and "ch + length + 1 > chend" with the corrected chend meaning, I removed the inner if-check. Signed-off-by: Tobias Stoeckmann <firstname.lastname@example.org>
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