Lennart Poettering
893e0f8fb6
Our journal code is generally supposed to be written in a fashion that the underlying file can be deallocated any time, i.e. our mmap of it suddenly becomes all zeroes. The idea is that we catch that when parsing everything. For that to work safely we need to make sure that when doing arithmetics or comparisons on values read from the map we don't run into TTOCTTOU issues when determining validity. Hence we need to copy out the values before use and operate on the copies. This requires some special care since the C compiler could suppress our copies as optimization. Hence use the new READ_NOW() macro to force a copy by using memcpy(), and use it whenever we start doing an arithmetic operation on it, or validity checking of multiple steps. Fixes: #14943
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