libct/nsenter: fix logging race in nsexec (regression in rc94) #3120
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I think this is a candidate for backporting to 1.0 -- while the race is rare, the consequences are fatal. |
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AkihiroSuda
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As reported in issue 3119, there is a race in nsexec logging that can lead to garbled json received by log forwarder, which complains about it with a "failed to decode" error. This happens because dprintf (used since the very beginning of nsexec logging introduced in commit ba3cabf) relies on multiple write(2) calls, and with additional logging added by 64bb59f a race is possible between runc init parent and its children. The fix is to prepare a string and write it using a single call to write(2). [v2: NULLify json on error from asprintf] Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
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As reported in issue #3119, there is a race in nsexec logging
that can lead to garbled json received by log forwarder, which
complains about it with a "failed to decode" error.
This happens because dprintf (used since the very beginning of nsexec
logging introduced in commit ba3cabf) relies on multiple write(2)
calls, and with additional logging added by 64bb59f (appeared in rc94)
a race is possible between runc init parent and its children.
The fix is to prepare a string and write it using a single call to
write(2).
Fixes: #3119
Practically, though, debug logging is not needed in 99.9% of all cases,
and so PR #3114 (commit b1bc762) eliminates the possibility
of it having this race in the first place. Yet I think this fix makes sense.
1.0 backport: #3130