fix: handle concurrent/interrupted processes to avoid file corruption (LP: #2126805)#11
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jdstrand wants to merge 12 commits into
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fix: handle concurrent/interrupted processes to avoid file corruption (LP: #2126805)#11jdstrand wants to merge 12 commits into
jdstrand wants to merge 12 commits into
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close_files() rewrote the target in place: shutil.copy() truncates the live file and rewrites it through a buffered stream. Every 'ufw insert' or 'ufw delete' therefore had a window where user.rules on disk was empty or cut mid-line and concurrent 'ufw status' printed rules from that broken state. Furthermore, a crash, power loss or SIGKILL mid-copy left the truncation on disk. Create the tempfile next to the target instead of in TMPDIR, fsync it, preserve the original's mode/ownership, and os.rename() it over the original (plus a best-effort directory fsync for power-loss safety). Readers and crashes now only ever see a complete old or complete new file. This also covers ufw.conf and the default policy files, which go through the same helpers.
main_ufw() constructed the UFWFrontend before create_lock() and UFWFronted parses user.rules, user6.rules and the configuration files. Every ufw process therefore acted on a snapshot taken while another process could be mid-update where a rule change could rewrite the whole rules file from that stale snapshot. Compute the lockfile path and take the lock before constructing the frontend, so the whole read-modify-write cycle sits inside the critical section.
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