thodg/libgit2/tests/commit

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  • Hash : 6daeb4fb
    Author : Patrick Steinhardt
    Date : 2018-11-09T19:32:08 

    signature: fix out-of-bounds read when parsing timezone offset

When parsing a signature's timezone offset, we first check whether there
is a timezone at all by verifying that there are still bytes left to
read following the time itself. The check thus looks like `time_end + 1
< buffer_end`, which is actually correct in this case. After setting the
timezone's start pointer to that location, we compute the remaining
bytes by using the formula `buffer_end - tz_start + 1`, re-using the
previous `time_end + 1`. But this is in fact missing the braces around
`(tz_start + 1)`, thus leading to an overestimation of the remaining
bytes by a length of two. In case of a non-NUL terminated buffer, this
will result in an overflow.

The function `git_signature__parse` is only used in two locations. First
is `git_signature_from_buffer`, which only accepts a string without a
length. The string thus necessarily has to be NUL terminated and cannot
trigger the issue.

The other function is `git_commit__parse_raw`, which can in fact trigger
the error as it may receive non-NUL terminated commit data. But as
objects read from the ODB are always NUL-terminated by us as a
cautionary measure, it cannot trigger the issue either.

In other words, this error does not have any impact on security.

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