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|ID||Project||Category||View Status||Date Submitted||Last Update|
|0005568||OCaml||OCaml otherlibs||public||2012-03-30 23:44||2013-08-05 12:22|
|Target Version||4.01.0+dev||Fixed in Version||4.01.0+dev|
|Summary||0005568: Unix.open_flag lacks O_CLOEXEC|
|Description|| O_CLOEXEC (Since Linux 2.6.23)|
Enable the close-on-exec flag for the new file descriptor.
Specifying this flag permits a program to avoid additional
fcntl(2) F_SETFD operations to set the FD_CLOEXEC flag. Addi-
tionally, use of this flag is essential in some multithreaded
programs since using a separate fcntl(2) F_SETFD operation to
set the FD_CLOEXEC flag does not suffice to avoid race condi-
tions where one thread opens a file descriptor at the same time
as another thread does a fork(2) plus execve(2).
There also some other flags missing but O_CLOEXEC has serious security implications.
|Tags||No tags attached.|
See note in PR#5569.
I support this because it avoids a race condition between opening a file and executing a command in a multi-threaded app. If you don't open with O_CLOEXEC, it can happen that the exec() is done between open() and the fcntl() setting the flag, and the file remains open in the child process. See also PR#5256.
O_CLOEXEC is covered by POSIX.
Of course, this is only a partial solution to the mentioned problem, but this not our issue, but POSIX': The other syscalls creating file descriptors don't have an O_CLOEXEC flag.
I would rather consider this a parent of 0005569, not a child.
Be advised that this wouldn't be just usefull for Unix.open_file. Other modules (extunix, lwt, ...) are using Unix.open_flags for syscalls that do accept O_CLOEXEC and would benefit from supporting a race-free CLOEXEC, too.
|Add O_CLOEXEC flag to Unix.openfile, with emulation if not supported by the OS. Commits r13961 on version/4.01 and r13962 on trunk. Win32 implementation needs testing.|
Upstream patches to Lwt/Core have now been applied to OPAM, to fix the builds with the new flag.
|I'm not sure if emulation is the right thing to do if the OS does not support the flag. You can't emulate it atomically and then you have the race condition back. It might be saver to fail if O_CLOEXEC is not supported.|
|2012-03-30 23:44||goswin||New Issue|
|2012-04-01 00:28||doligez||Relationship added||child of 0005569|
|2012-04-01 00:30||doligez||Note Added: 0007256|
|2012-04-01 00:30||doligez||Status||new => feedback|
|2012-04-02 10:47||gerd||Note Added: 0007260|
|2012-04-03 15:18||xleroy||Relationship added||related to 0005256|
|2012-04-03 15:28||goswin||Note Added: 0007270|
|2012-04-03 15:28||goswin||Status||feedback => new|
|2012-04-10 17:40||doligez||Status||new => acknowledged|
|2012-07-09 17:42||doligez||Target Version||=> 4.01.0+dev|
|2012-07-31 13:36||doligez||Target Version||4.01.0+dev => 4.00.1+dev|
|2012-08-06 18:33||xleroy||Target Version||4.00.1+dev => 4.01.0+dev|
|2013-08-01 14:16||xleroy||Note Added: 0010062|
|2013-08-01 14:16||xleroy||Status||acknowledged => resolved|
|2013-08-01 14:16||xleroy||Resolution||open => fixed|
|2013-08-01 14:16||xleroy||Fixed in Version||=> 4.01.0+dev|
|2013-08-03 23:05||avsm||Note Added: 0010087|
|2013-08-05 12:22||goswin||Note Added: 0010113|
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