Austin Group issue #411 [1] proposes that posix_spawn file action
posix_spawn_file_actions_adddup2 resets the close-on-exec when
source and destination refer to same file descriptor.
It solves the issue on multi-thread applications which uses
close-on-exec as default, and want to hand-chose specifically
file descriptor to purposefully inherited into a child process.
Current approach to achieve this scenario is to use two adddup2 file
actions and a temporary file description which do not conflict with
any other, coupled with a close file action to avoid leaking the
temporary file descriptor. This approach, besides being complex,
may fail with EMFILE/ENFILE file descriptor exaustion.
This can be more easily accomplished with an in-place removal of
FD_CLOEXEC. Although the resulting adddup2 semantic is slight
different than dup2 (equal file descriptors should be handled as
no-op), the proposed possible solution are either more complex
(fcntl action which a limited set of operations) or results in
unrequired operations (dup3 which also returns EINVAL for same
file descriptor).
Checked on aarch64-linux-gnu.
[BZ #23640]
* posix/tst-spawn.c (do_prepare, handle_restart, do_test): Add
posix_spawn_file_actions_adddup2 test to check O_CLOCEXEC reset.
* sysdeps/unix/sysv/linux/spawni.c (__spawni_child): Add
close-on-exec reset for adddup2 file action.
* sysdeps/posix/spawni.c (__spawni_child): Likewise.
[1] http://austingroupbugs.net/view.php?id=411
Along with posix_spawn_file_actions_addchdir,
posix_spawn_file_actions_addfchdir is the subject of a change proposal
for POSIX: <http://austingroupbugs.net/view.php?id=1208>
This patch uses posix_spawn on system implementation. On Linux this has
the advantage of much lower memory consumption (usually 32 Kb minimum for
the mmap stack area).
Although POSIX does not require, glibc system implementation aims to be
thread and cancellation safe. The cancellation code is moved to generic
implementation and enabled iff SIGCANCEL is defined (similar on how the
cancellation handler is enabled on nptl-init.c).
Checked on x86_64-linux-gnu, i686-linux-gnu, aarch64-linux-gnu,
arm-linux-gnueabihf, and powerpc64le-linux-gnu.
* sysdeps/unix/sysv/linux/spawni.c (__spawni_child): Use
__sigismember instead of sigismember.
* sysdeps/posix/system.c [SIGCANCEL] (cancel_handler_args,
cancel_handler): New definitions.
(CLEANUP_HANDLER, CLEANUP_RESET): Likewise.
(DO_LOCK, DO_UNLOCK, INIT_LOCK, ADD_REF, SUB_REF): Remove.
(do_system): Use posix_spawn instead of fork and execl and remove
reentracy code.
* sysdeps/generic/not-errno.h (__kill_noerrno): New prototype.
* sysdeps/unix/sysv/linux/not-errno.h (__kill_noerrno): Likewise.
* sysdeps/unix/sysv/linux/ia64/system.c: Remove file.
* sysdeps/unix/sysv/linux/s390/system.c: Likewise.
* sysdeps/unix/sysv/linux/sparc/system.c: Likewise.
* sysdeps/unix/sysv/linux/system.c: Likewise.
If glibc is built with gcc 8 and -march=z900,
the testcase posix/tst-spawn4-compat crashes with a segfault.
In function maybe_script_execute, the new_argv array is dynamically
initialized on stack with (argc + 1) elements.
The function wants to add _PATH_BSHELL as the first argument
and writes out of bounds of new_argv.
There is an off-by-one because maybe_script_execute fails to count
the terminating NULL when sizing new_argv.
ChangeLog:
* sysdeps/unix/sysv/linux/spawni.c (maybe_script_execute):
Increment size of new_argv by one.
Current posix_spawnp implementation wrongly tries to execute invalid
binaries (for instance script without shebang) as a shell script in
non compat mode. It was a regression introduced by
9ff72da471 when __spawni started to use
__execvpe instead of __execve (glibc __execvpe try to execute ENOEXEC
as shell script regardless).
This patch fixes it by using an internal symbol (__execvpex) with the
faulty semantic (since compat mode is handled by spawni.c itself).
It was reported by Daniel Drake on libc-help [1].
Checked on x86_64-linux-gnu and i686-linux-gnu.
[BZ #23264]
* include/unistd.h (__execvpex): New prototype.
* posix/Makefile (tests): Add tst-spawn4.
(tests-internal): Add tst-spawn4-compat.
* posix/execvpe.c (__execvpe_common, __execvpex): New functions.
* posix/tst-spawn4-compat.c: New file.
* posix/tst-spawn4.c: Likewise.
* sysdeps/unix/sysv/linux/spawni.c (__spawni): Do not interpret invalid
binaries as shell scripts.
* sysdeps/posix/spawni.c (__spawni): Likewise.
[1] https://sourceware.org/ml/libc-help/2018-06/msg00012.html
This patch renames the nptl-signals.h header to internal-signals.h.
On Linux the definitions and functions are not only NPTL related, but
used for other POSIX definitions as well (for instance SIGTIMER for
posix times, SIGSETXID for id functions, and signal block/restore
helpers) and since generic functions will be places and used in generic
implementation it makes more sense to decouple it from NPTL.
Checked on x86_64-linux-gnu.
* sysdeps/nptl/nptl-signals.h: Move to ...
* sysdeps/generic/internal-signals.h: ... here. Adjust internal
comments.
* sysdeps/unix/sysv/linux/internal-signals.h: Add include guards.
(__nptl_is_internal_signal): Rename to __is_internal_signal.
(__nptl_clear_internal_signals): Rename to __clear_internal_signals.
* sysdeps/unix/sysv/linux/raise.c: Adjust nptl-signal.h to
include-signals.h rename.
* nptl/pthreadP.h: Likewise.
* sysdeps/unix/sysv/linux/spawni.c (__spawni_child): Call
__is_internal_signal instead of __nptl_is_internal_signal.
As shown in some buildbot issues on aarch64 and powerpc, calling
clone (VFORK) and waitpid (WNOHANG) does not guarantee the child
is ready to be collected. This patch changes the call back to 0
as before fe05e1cb6d fix.
This change can lead to the scenario 4.3 described in the commit,
where the waitpid call can hang undefinitely on the call. However
this is also a very unlikely and also undefinied situation where
both the caller is trying to terminate a pid before posix_spawn
returns and the race pid reuse is triggered. I don't see how to
correct handle this specific situation within posix_spawn.
Checked on x86_64-linux-gnu, aarch64-linux-gnu and
powerpc64-linux-gnu.
* sysdeps/unix/sysv/linux/spawni.c (__spawnix): Use 0 instead of
WNOHANG in waitpid call.
As noted by Florian Weimer, current Linux posix_spawn implementation
can trigger an assert if the auxiliary process is terminated before
actually setting the err member:
340 /* Child must set args.err to something non-negative - we rely on
341 the parent and child sharing VM. */
342 args.err = -1;
[...]
362 new_pid = CLONE (__spawni_child, STACK (stack, stack_size), stack_size,
363 CLONE_VM | CLONE_VFORK | SIGCHLD, &args);
364
365 if (new_pid > 0)
366 {
367 ec = args.err;
368 assert (ec >= 0);
Another possible issue is killing the child between setting the err and
actually calling execve. In this case the process will not ran, but
posix_spawn also will not report any error:
269
270 args->err = 0;
271 args->exec (args->file, args->argv, args->envp);
As suggested by Andreas Schwab, this patch removes the faulty assert
and also handles any signal that happens before fork and execve as the
spawn was successful (and thus relaying the handling to the caller to
figure this out). Different than Florian, I can not see why using
atomics to set err would help here, essentially the code runs
sequentially (due CLONE_VFORK) and I think it would not be legal the
compiler evaluate ec without checking for new_pid result (thus there
is no need to compiler barrier).
Summarizing the possible scenarios on posix_spawn execution, we
have:
1. For default case with a success execution, args.err will be 0, pid
will not be collected and it will be reported to caller.
2. For default failure case, args.err will be positive and the it will
be collected by the waitpid. An error will be reported to the
caller.
3. For the unlikely case where the process was terminated and not
collected by a caller signal handler, it will be reported as succeful
execution and not be collected by posix_spawn (since args.err will
be 0). The caller will need to actually handle this case.
4. For the unlikely case where the process was terminated and collected
by caller we have 3 other possible scenarios:
4.1. The auxiliary process was terminated with args.err equal to 0:
it will handled as 1. (so it does not matter if we hit the pid
reuse race since we won't possible collect an unexpected
process).
4.2. The auxiliary process was terminated after execve (due a failure
in calling it) and before setting args.err to -1: it will also
be handle as 1. but with the issue of not be able to report the
caller a possible execve failures.
4.3. The auxiliary process was terminated after args.err is set to -1:
this is the case where it will be possible to hit the pid reuse
case where we will need to collected the auxiliary pid but we
can not be sure if it will be expected one. I think for this
case we need to actually change waitpid to use WNOHANG to avoid
hanging indefinitely on the call and report an error to caller
since we can't differentiate between a default failure as 2.
and a possible pid reuse race issue.
Checked on x86_64-linux-gnu.
* sysdeps/unix/sysv/linux/spawni.c (__spawnix): Handle the case where
the auxiliary process is terminated by a signal before calling _exit
or execve.
The internal 'ret' variable in '__spawni_child' function is not
used after assignment in most cases.
Checked on x86_64-linux-gnu.
* sysdeps/unix/sysv/linux/spawni.c (__spawni_child): Remove ununsed
assignment.
This patch adds support for the POSIX_SPAWN_SETSID flag.
It was recently accepted by the Austin Group:
http://austingroupbugs.net/view.php?id=1044
Checked on x86_64
Daurnimator <quae@daurnimator.com>
Adhemerval Zanella <adhemerval.zanella@linaro.org>
[BZ #21340]
* posix/Makefile (tests): Add tst-posix_spawn-setsid to list of tests.
* posix/spawn.h: define POSIX_SPAWN_SETSID flag.
* posix/spawnattr_setflags.c (ALL_FLAGS): Add POSIX_SPAWN_SETSID to
valid flags.
* posix/tst-posix_spawn-setsid.c: Add test for POSIX_SPAWN_SETSID.
* sysdeps/mach/hurd/spawni.c (__spawni): Implementation of
POSIX_SPAWN_SETSID.
* sysdeps/posix/spawni.c (__spawni): Likewise.
* sysdeps/unix/sysv/linux/spawni.c (__spawni_child): Likewise.
* NEWS: Add note about POSIX_SPAWN_SETSID support.
When glibc is built with -fstack-check, trying to use posix_spawn can
lead to segfaults due to gcc internally probing stack memory too far.
The new spawn API will allocate a minimum of 1 page, but the stack
checking logic might probe a couple of pages. When it tries to walk
them, everything falls apart.
The gcc internal docs [1] state the default interval checking is one
page. Which means we need two pages (the current one, and the next
probed). No target currently defines it larger.
Further, it mentions that the default minimum stack size needed to
recover from an overflow is 4/8KiB for sjlj or 8/12KiB for others.
But some Linux targets (like mips and ppc) go up to 16KiB (and some
non-Linux targets go up to 24KiB).
Let's create each child with a minimum of 32KiB slack space to support
them all, and give us future breathing room.
No test is added as existing ones crash. Even a simple call is
enough to trigger the problem:
char *argv[] = { "/bin/ls", NULL };
posix_spawn(NULL, "/bin/ls", NULL, NULL, argv, NULL);
[1] https://gcc.gnu.org/onlinedocs/gcc-6.3.0/gccint/Stack-Checking.html
The ia64-specific clone2 call expects the base of the stack mapping and
the stack size as sep arguments, not an initial stack value as on other
stack-grows-down architectures. Reuse the stack-grows-up macro so we
pass in the right stack base.
Reported-by: Matt Turner <mattst88@gentoo.org>
posix/wordexp-test.c used libc-internal.h for PTR_ALIGN_DOWN; similar
to what was done with libc-diag.h, I have split the definitions of
cast_to_integer, ALIGN_UP, ALIGN_DOWN, PTR_ALIGN_UP, and PTR_ALIGN_DOWN
to a new header, libc-pointer-arith.h.
It then occurred to me that the remaining declarations in libc-internal.h
are mostly to do with early initialization, and probably most of the
files including it, even in the core code, don't need it anymore. Indeed,
only 19 files actually need what remains of libc-internal.h. 23 others
need libc-diag.h instead, and 12 need libc-pointer-arith.h instead.
No file needs more than one of them, and 16 don't need any of them!
So, with this patch, libc-internal.h stops including libc-diag.h as
well as losing the pointer arithmetic macros, and all including files
are adjusted.
* include/libc-pointer-arith.h: New file. Define
cast_to_integer, ALIGN_UP, ALIGN_DOWN, PTR_ALIGN_UP, and
PTR_ALIGN_DOWN here.
* include/libc-internal.h: Definitions of above macros
moved from here. Don't include libc-diag.h anymore either.
* posix/wordexp-test.c: Include stdint.h and libc-pointer-arith.h.
Don't include libc-internal.h.
* debug/pcprofile.c, elf/dl-tunables.c, elf/soinit.c, io/openat.c
* io/openat64.c, misc/ptrace.c, nptl/pthread_clock_gettime.c
* nptl/pthread_clock_settime.c, nptl/pthread_cond_common.c
* string/strcoll_l.c, sysdeps/nacl/brk.c
* sysdeps/unix/clock_settime.c
* sysdeps/unix/sysv/linux/i386/get_clockfreq.c
* sysdeps/unix/sysv/linux/ia64/get_clockfreq.c
* sysdeps/unix/sysv/linux/powerpc/get_clockfreq.c
* sysdeps/unix/sysv/linux/sparc/sparc64/get_clockfreq.c:
Don't include libc-internal.h.
* elf/get-dynamic-info.h, iconv/loop.c
* iconvdata/iso-2022-cn-ext.c, locale/weight.h, locale/weightwc.h
* misc/reboot.c, nis/nis_table.c, nptl_db/thread_dbP.h
* nscd/connections.c, resolv/res_send.c, soft-fp/fmadf4.c
* soft-fp/fmasf4.c, soft-fp/fmatf4.c, stdio-common/vfscanf.c
* sysdeps/ieee754/dbl-64/e_lgamma_r.c
* sysdeps/ieee754/dbl-64/k_rem_pio2.c
* sysdeps/ieee754/flt-32/e_lgammaf_r.c
* sysdeps/ieee754/flt-32/k_rem_pio2f.c
* sysdeps/ieee754/ldbl-128/k_tanl.c
* sysdeps/ieee754/ldbl-128ibm/k_tanl.c
* sysdeps/ieee754/ldbl-96/e_lgammal_r.c
* sysdeps/ieee754/ldbl-96/k_tanl.c, sysdeps/nptl/futex-internal.h:
Include libc-diag.h instead of libc-internal.h.
* elf/dl-load.c, elf/dl-reloc.c, locale/programs/locarchive.c
* nptl/nptl-init.c, string/strcspn.c, string/strspn.c
* malloc/malloc.c, sysdeps/i386/nptl/tls.h
* sysdeps/nacl/dl-map-segments.h, sysdeps/x86_64/atomic-machine.h
* sysdeps/unix/sysv/linux/spawni.c
* sysdeps/x86_64/nptl/tls.h:
Include libc-pointer-arith.h instead of libc-internal.h.
* elf/get-dynamic-info.h, sysdeps/nacl/dl-map-segments.h
* sysdeps/x86_64/atomic-machine.h:
Add multiple include guard.
On posix_spawn open file action (issued by posix_spawn_file_actions_addopen)
POSIX states that if fildes was already an open file descriptor, it shall be
closed before the new file is openedi [1]. This avoid pontential issues when
posix_spawn plus addopen action is called with the process already at maximum
number of file descriptor opened and also for multiple actions on single-open
special paths (like /dev/watchdog).
This fixes its behavior on Linux posix_spawn implementation and also adds
a tests to check for its behavior.
Checked on x86_64.
* posix/Makefile (tests): Add tst-spawn3.
* posix/tst-spawn3.c: New file.
* sysdeps/unix/sysv/linux/spawni.c (__spawni_child): Close file descriptor
if it is already opened for open action.
[1] http://pubs.opengroup.org/onlinepubs/9699919799/functions/posix_spawn_file_actions_addclose.html
Using CLONE_VFORK already ensures that the parent does not run until the
child has either exec'ed succesfully or called _exit. Hence we don't
need to read from a CLOEXEC pipe to ensure proper synchronization - we
just make explicit use of the fact the the child and parent run in the
same VM, so the child can write an error code to a field of the
posix_spawn_args struct instead of sending it through a pipe.
To ensure that this mechanism really works, the parent initializes the
field to -1 and the child writes 0 before execing.
This eliminates some annoying bookkeeping that is necessary to avoid
the file actions from clobbering the write end of the pipe, and
getting rid of the pipe creation in the first place means fewer system
calls (four in the parent, usually one in the child) and fewer
chanches for the spawn to fail (e.g. if we're close to EMFILE).
Checked on x86_64 and i686.
* sysdeps/unix/sysv/linux/spawni.c (posix_spawn_args): Remove pipe
field, add err field.
(__spawni_child): Report error through err member instead of pipe.
(__spawnix): Likewise.
This patch correctly block and unblocks all signals when executing
Linux posix_spawn by using the __libc_signal_{un}block_all functions
instead of default sigprocmask. The latter might remove both
SIGCANCEL and SIGSETXID from the blocked signal list.
Checked on x86_64, i686, powerpc64le, and aarch64.
* sysdeps/unix/sysv/linux/spawni.c (__spawnix): Correctly block and unblock
all signals when executing the clone vfork child.
(SIGALL_SET): Remove macro.
This patch correctly enable and disable asynchronous cancellation on
Linux posix_spawn. Current code invert the logic by enabling and
disabling instead. It also adds a new test to check if posix_spawn
is not a cancellation entrypoint.
Checked on x86_64, i686, powerpc64le, and aarch64.
* nptl/Makefile (tests): Add tst-exec5.
* nptl/tst-exec5.c: New file.
* sysdeps/unix/sysv/linux/spawni.c (__spawni): Correctly enable and disable
asynchronous cancellation.
This patch call _exit instead of exit in failure case for the spawned
child in Linux posix_spawn{p} implementation.
Tested on x86_64.
[BZ #20178]
* sysdeps/unix/sysv/linux/spawni.c (__spawni_child): Call _exit
on failure instead of exit.
This patch fixes the implicit check style add in 2a69f853c for the
general convention one.
Checked on x86_64.
* sysdeps/unix/sysv/linux/spawni.c (__spawnix): Fix implict checks
style.
Current Linux posix_spawn spawn do not test if the pid argument is
valid before trying to update it for success case. This patch fixes
it.
Tested on x86_64 and i686.
* sysdeps/unix/sysv/linux/spawni.c (__spawnix): Fix invalid memory
access where posix_spawn success and pid argument is null.
* posix/tst-spawn.c (do_test): Add posix_spawn null pid argument for
success case.
This patch implements a new posix_spawn{p} implementation for Linux. The main
difference is it uses the clone syscall directly with CLONE_VM and CLONE_VFORK
flags and a direct allocated stack. The new stack and start function solves
most the vfork limitation (possible parent clobber due stack spilling). The
remaning issue are related to signal handling:
1. That no signal handlers must run in child context, to avoid corrupt
parent's state.
2. Child must synchronize with parent to enforce stack deallocation and
to possible return execv issues.
The first one is solved by blocking all signals in child, even NPTL-internal
ones (SIGCANCEL and SIGSETXID). The second issue is done by a stack allocation
in parent and a synchronization with using a pipe or waitpid (in case or error).
The pipe has the advantage of allowing the child signal an exec error (checked
with new tst-spawn2 test).
There is an inherent race condition in pipe2 usage for architectures that do not
support the syscall directly. In such cases the a pipe plus fctnl is used
instead and it may lead to file descriptor leak in parent (as decribed by fcntl
documentation).
The child process stack is allocate with a mmap with MAP_STACK flag using
default architecture stack size. Although it is slower than use a stack buffer
from parent, it allows some slack for the compatibility code to run scripts
with no shebang (which may use a buffer with size depending of argument list
count).
Performance should be similar to the vfork default posix implementation and
way faster than fork path (vfork on mostly linux ports are basically
clone with CLONE_VM plus CLONE_VFORK). The only difference is the syscalls
required for the stack allocation/deallocation.
It fixes BZ#10354, BZ#14750, and BZ#18433.
Tested on i386, x86_64, powerpc64le, and aarch64.
[BZ #14750]
[BZ #10354]
[BZ #18433]
* include/sched.h (__clone): Add hidden prototype.
(__clone2): Likewise.
* include/unistd.h (__dup): Likewise.
* posix/Makefile (tests): Add tst-spawn2.
* posix/tst-spawn2.c: New file.
* sysdeps/posix/dup.c (__dup): Add hidden definition.
* sysdeps/unix/sysv/linux/aarch64/clone.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/alpha/clone.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/arm/clone.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/hppa/clone.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/i386/clone.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/ia64/clone2.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/m68k/clone.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/microblaze/clone.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/mips/clone.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/nios2/clone.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/powerpc/powerpc32/clone.S (__clone):
Likewise.
* sysdeps/unix/sysv/linux/powerpc/powerpc64/clone.S (__clone):
Likewise.
* sysdeps/unix/sysv/linux/s390/s390-32/clone.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/s390/s390-64/clone.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/sh/clone.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/sparc/sparc32/clone.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/sparc/sparc64/clone.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/tile/clone.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/x86_64/clone.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/nptl-signals.h
(____nptl_is_internal_signal): New function.
* sysdeps/unix/sysv/linux/spawni.c: New file.
