Fix GH-16628: FPM logs are getting corrupted with this log statement #16680
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zlog_buf_prefix() can return a larger length than what actually was written due to its use of snprintf(). The code in zlog_stream_prefix_ex() does not take this into account, other callers do. What ends up happening then is that stream->length is set to the length as if snprintf() was able to write all bytes, causing stream->length to become larger than stream->buf.size, causing a segfault. In case the buffer was too small we try with a larger buffer up to a limit of zlog_limit. This makes sure that the stream length will remain bounded by the buffer size. This also adds assertions to make the programmer intent clear and catch this more easily in debug builds.
bukka
approved these changes
Nov 2, 2024
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zlog_buf_prefix() can return a larger length than what actually was written due to its use of snprintf(). The code in
zlog_stream_prefix_ex() does not take this into account, other callers do. What ends up happening then is that stream->length is set to the length as if snprintf() was able to write all bytes, causing stream->length to become larger than stream->buf.size, causing a segfault.
In case the buffer was too small we try with a larger buffer up to a limit of zlog_limit. This makes sure that the stream length will remain bounded by the buffer size.
This also adds assertions to make the programmer intent clear and catch this more easily in debug builds.