Fix null file descriptor being closed when used as redirection for standard fd of child processes #957
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
MisterDA
force-pushed
the
cloexec-proc-dev-null-fixes
branch
from
7b22822 to
536e884
Compare
MisterDA
force-pushed
the
cloexec-proc-dev-null-fixes
branch
from
536e884 to
0d1e09a
Compare
|
Thanks for the review, applied and rebased your suggestions. |
- don't swallow stderr of the subprocess; - use the Unix module directly in the dummy subprocess to avoid buffering and errors disappearing.
On Unix O_CLOEXEC on a file descriptor was introduced in 9de01c9. It is superfluous and buggy: we're already in the forked process at this point! So setting it cloexec between the actual fork and exec will close the file descriptor in the sub-process, making all read and writes to it fail. On Windows, it is wrong as well: we want the child process to inherit the NUL file descriptor, so it mustn't be cloexec, and it must be closed after the spawn in the parent process. It wasn't caught in the tests because they weren't complete enough, fixed in the parent commit. The files descriptors must remain keep-on-exec, so we set this file instead explicitly.
MisterDA
force-pushed
the
cloexec-proc-dev-null-fixes
branch
from
0d1e09a to
15c65b5
Compare
|
Tested locally: the tests fail when the src changes are reverted. |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
So, this is my mess-up, probably because I ignored the error, and because my tests weren't comprehensive enough.
In my eagerness of cloexec-ing file descriptors, I added one too many
O_CLOEXECflag. When one wants to redirect a standard file descriptor of a child process (giving`Dev_nullto~stdin,~stdout, or~stderrarguments of functions inLwt_process, my code introduced in 9de01c9 will actually close the file descriptor for the child process, which means that any read/write to this standard fd will fail. It is likely that the child process will exit with an error, the opposite of the intent, of course.I've improved the tests, fixed the bug, simplified a bit the code and used explicit close-on-exec or keep-on-exec everywhere.