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posix: Add posix_spawn_file_actions_addclosefrom_np

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This patch adds a way to close a range of file descriptors on
posix_spawn as a new file action.  The API is similar to the one
provided by Solaris 11 [1], where the file action causes the all open
file descriptors greater than or equal to input on to be closed when
the new process is spawned.

The function posix_spawn_file_actions_addclosefrom_np is safe to be
implemented by iterating over /proc/self/fd, since the Linux spawni.c
helper process does not use CLONE_FILES, so its has own file descriptor
table and any failure (in /proc operation) aborts the process creation
and returns an error to the caller.

I am aware that this file action might be redundant to the current
approach of POSIX in promoting O_CLOEXEC in more interfaces. However
O_CLOEXEC is still not the default and for some specific usages, the
caller needs to close all possible file descriptors to avoid them
leaking.  Some examples are CPython (discussed in BZ#10353) and OpenJDK
jspawnhelper [2] (where OpenJDK spawns a helper process to exactly
closes all file descriptors).  Most likely any environment which calls
functions that might open file descriptor under the hood and aim to use
posix_spawn might face the same requirement.

Checked on x86_64-linux-gnu and i686-linux-gnu on kernel 5.11 and 4.15.

[1] https://docs.oracle.com/cd/E36784_01/html/E36874/posix-spawn-file-actions-addclosefrom-np-3c.html
[2] https://github.com/openjdk/jdk/blob/master/src/java.base/unix/native/libjava/childproc.c#L82
This commit is contained in:
Adhemerval Zanella
2021-03-10 12:26:33 -03:00
parent 607449506f
commit 882d6e17bc
49 changed files with 483 additions and 22 deletions
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8
sysdeps/unix/sysv/linux/closefrom_fallback.c
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@ -22,9 +22,11 @@
#include <stdbool.h>
/* Fallback code: iterates over /proc/self/fd, closing each file descriptor
that fall on the criteria. */
that fall on the criteria. If DIRFD_FALLBACK is set, a failure on
/proc/self/fd open will trigger a fallback that tries to close a file
descriptor before proceed. */
_Bool
__closefrom_fallback (int from)
__closefrom_fallback (int from, _Bool dirfd_fallback)
{
bool ret = false;
@ -33,7 +35,7 @@ __closefrom_fallback (int from)
if (dirfd == -1)
{
/* The closefrom should work even when process can't open new files. */
if (errno == ENOENT)
if (errno == ENOENT || !dirfd_fallback)
goto err;
for (int i = from; i < INT_MAX; i++)