Revert "sshdriver: Prevent timeout from deadlock" #1288
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This reverts commit b8f059f. OpenSSH < 8.5 called with -f waits for the stderr pipe to be closed before forking. [1] fixes this behavior. The labgrid commit to be reverted calls communicate(), relying on a timely fork. Affected OpenSSH versions now run into a TimeoutExpired exception on communicate() leading to an ExecutionError being raised in labgrid. A wait() with timeout was used since the initial implementation [2]. We wanted to make sure that we don't depend on the state of the pipes, so use of wait() was intentional, as it directly covers the interesting cases: - immediate abort (due to a config error or similar) - normal startup (parent process exits after fork) - hang (via wait() timeout) Reverting the problematic commit avoids the complexity of having to maintain two different ways to start SSH as suggested in [3]. If timeouts still occur after the revert, we should implement this suggestion [4]. Discussion that lead to this patch can be found in the PR introducing the problematic commit [5] as well as in [3]. The other commit [6] in the PR [5] has a similar approach for `labgrid.util.SSHConnection._start_own_master()`. It shouldn't be problematic though: The ssh process is not expected to fork as it is not called with -f. [1] OpenSSH: 396d32f3a ("upstream: There are lots of place where we want to redirect stdin,") [2] e4862fa ("SSHDriver: ControlMaster & Driver") [3] labgrid-project#1278 [4] labgrid-project#1265 (comment) [5] labgrid-project#1265 [6] f9ca024 ("ssh: Prevent timeout from deadlock") Signed-off-by: Bastian Krause <[email protected]>
Codecov ReportAttention:
Additional details and impacted files@@ Coverage Diff @@
## master #1288 +/- ##
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- Coverage 63.0% 63.0% -0.1%
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Files 160 160
Lines 11902 11901 -1
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- Hits 7502 7501 -1
Misses 4400 4400
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Emantor
approved these changes
Oct 21, 2023
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Description
This reverts commit b8f059f.
OpenSSH < 8.5 called with -f waits for the stderr pipe to be closed before forking. [1] fixes this behavior.
The labgrid commit to be reverted calls
communicate(), relying on a timely fork. Affected OpenSSH versions now run into a TimeoutExpired exception oncommunicate()leading to an ExecutionError being raised in labgrid.A
wait()with timeout was used since the initial implementation [2]. We wanted to make sure that we don't depend on the state of the pipes, so use of wait() was intentional, as it directly covers the interesting cases:wait()timeout)Reverting the problematic commit avoids the complexity of having to maintain two different ways to start SSH as suggested in [3].
If timeouts still occur after the revert, we should implement this suggestion [4].
Discussion that lead to this patch can be found in the PR introducing the problematic commit [5] as well as in [3].
The other commit [6] in the PR [5] has a similar approach for
labgrid.util.SSHConnection._start_own_master(). It shouldn't be problematic though: The ssh process is not expected to fork as it is not called with -f.[1] openssh/openssh-portable@396d32f ("upstream: There are lots of place where we want to redirect stdin,")
[2] e4862fa ("SSHDriver: ControlMaster & Driver")
[3] #1278
[4] #1265 (comment)
[5] #1265
[6] f9ca024 ("ssh: Prevent timeout from deadlock")
Checklist
Fixes #1265
Closes #1278