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Re: [PATCH v2] Use execveat syscall in fexecve
On 11/09/2017 07:23, Andreas Schwab wrote:
> By using execveat we no longer depend on /proc. The execveat syscall was
> introduced in 3.19, except for a few late comers.
>
> * sysdeps/unix/sysv/linux/fexecve.c (fexecve) [__NR_execveat]: Try
> execveat first.
> [!__ASSUME_EXECVEAT]: Fall back to /proc if execveat is
> unimplemented.
> * sysdeps/unix/sysv/linux/kernel-features.h (__ASSUME_EXECVEAT)
> [__LINUX_KERNEL_VERSION >= 0x031300]: Define.
> * sysdeps/unix/sysv/linux/alpha/kernel-features.h
> (__ASSUME_EXECVEAT) [__LINUX_KERNEL_VERSION < 0x040200]: Undef.
> * sysdeps/unix/sysv/linux/hppa/kernel-features.h
> (__ASSUME_EXECVEAT) [__LINUX_KERNEL_VERSION < 0x040000]: Undef.
> * sysdeps/unix/sysv/linux/microblaze/kernel-features.h
> (__ASSUME_EXECVEAT) [__LINUX_KERNEL_VERSION < 0x040000]: Undef.
> * posix/Makefile (tests): Add tst-fexecve.
> * posix/tst-fexecve.c: New file.
> ---
> posix/Makefile | 2 +-
> posix/tst-fexecve.c | 88 ++++++++++++++++++++++
> sysdeps/unix/sysv/linux/alpha/kernel-features.h | 5 ++
> sysdeps/unix/sysv/linux/fexecve.c | 15 ++++
> sysdeps/unix/sysv/linux/hppa/kernel-features.h | 5 ++
> sysdeps/unix/sysv/linux/kernel-features.h | 5 ++
> .../unix/sysv/linux/microblaze/kernel-features.h | 5 ++
> 7 files changed, 124 insertions(+), 1 deletion(-)
> create mode 100644 posix/tst-fexecve.c
>
> diff --git a/posix/Makefile b/posix/Makefile
> index 4021e4f19e..75d905b922 100644
> --- a/posix/Makefile
> +++ b/posix/Makefile
> @@ -94,7 +94,7 @@ tests := test-errno tstgetopt testfnm runtests runptests \
> tst-fnmatch4 tst-fnmatch5 \
> tst-posix_spawn-fd tst-posix_spawn-setsid \
> tst-posix_fadvise tst-posix_fadvise64 \
> - tst-sysconf-empty-chroot
> + tst-sysconf-empty-chroot tst-fexecve
> tests-internal := bug-regex5 bug-regex20 bug-regex33 \
> tst-rfc3484 tst-rfc3484-2 tst-rfc3484-3
> xtests := bug-ga2
> diff --git a/posix/tst-fexecve.c b/posix/tst-fexecve.c
> new file mode 100644
> index 0000000000..2409102e21
> --- /dev/null
> +++ b/posix/tst-fexecve.c
> @@ -0,0 +1,88 @@
> +/* Copyright (C) 2017 Free Software Foundation, Inc.
> + This file is part of the GNU C Library.
> +
> + The GNU C Library is free software; you can redistribute it and/or
> + modify it under the terms of the GNU Lesser General Public
> + License as published by the Free Software Foundation; either
> + version 2.1 of the License, or (at your option) any later version.
> +
> + The GNU C Library is distributed in the hope that it will be useful,
> + but WITHOUT ANY WARRANTY; without even the implied warranty of
> + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
> + Lesser General Public License for more details.
> +
> + You should have received a copy of the GNU Lesser General Public
> + License along with the GNU C Library; if not, see
> + <http://www.gnu.org/licenses/>. */
> +
> +#include <unistd.h>
> +#include <errno.h>
> +#include <fcntl.h>
> +#include <sys/wait.h>
> +
> +#include <support/check.h>
> +
> +/* Try executing "/bin/sh -c true", using FD opened on /bin/sh. */
> +static int
> +try_fexecve (int fd)
> +{
> + pid_t pid = fork ();
> +
> + if (pid == 0)
> + {
> + static const char *const argv[] = {
> + "/bin/sh", "-c", "true", NULL
> + };
> + fexecve (fd, (char *const *) argv, environ);
> + _exit (errno);
> + }
> + if (pid < 0)
> + FAIL_RET ("fork failed: %m");
> +
> + pid_t termpid;
> + int status;
> + termpid = TEMP_FAILURE_RETRY (waitpid (pid, &status, 0));
> + if (termpid == -1)
> + FAIL_RET ("waitpid failed: %m");
> + if (termpid != pid)
> + FAIL_RET ("waitpid returned %ld != %ld",
> + (long int) termpid, (long int) pid);
> + if (!WIFEXITED (status))
> + FAIL_RET ("child hasn't exited normally");
> +
> + /* If fexecve is unimplemented mark this test as UNSUPPORTED. */
> + if (WEXITSTATUS (status) == ENOSYS)
> + FAIL_UNSUPPORTED ("fexecve is unimplemented");
> +
> + if (WEXITSTATUS (status) != 0)
> + {
> + errno = WEXITSTATUS (status);
> + FAIL_RET ("fexecve failed: %m");
> + }
> + return 0;
> +}
> +
> +static int
> +do_test (void)
> +{
> + int fd;
> + int ret;
> +
> + fd = open ("/bin/sh", O_RDONLY);
> + if (fd < 0)
> + FAIL_UNSUPPORTED ("/bin/sh cannot be opened: %m");
> + ret = try_fexecve (fd);
> + close (fd);
> +
> +#ifdef O_PATH
> + fd = open ("/bin/sh", O_RDONLY | O_PATH);
> + if (fd < 0)
> + FAIL_UNSUPPORTED ("/bin/sh cannot be opened (O_PATH): %m");
> + ret |= try_fexecve (fd);
> + close (fd);
> +#endif
> +
> + return ret;
> +}
> +
> +#include <support/test-driver.c>
> diff --git a/sysdeps/unix/sysv/linux/alpha/kernel-features.h b/sysdeps/unix/sysv/linux/alpha/kernel-features.h
> index 53f7611f93..5bc2ddb713 100644
> --- a/sysdeps/unix/sysv/linux/alpha/kernel-features.h
> +++ b/sysdeps/unix/sysv/linux/alpha/kernel-features.h
> @@ -35,4 +35,9 @@
> #define __ASSUME_RECV_SYSCALL 1
> #define __ASSUME_SEND_SYSCALL 1
>
> +/* Support for the execveat syscall was added in 4.2. */
> +#if __LINUX_KERNEL_VERSION < 0x040200
> +# undef __ASSUME_EXECVEAT
> +#endif
> +
> #endif /* _KERNEL_FEATURES_H */
> diff --git a/sysdeps/unix/sysv/linux/fexecve.c b/sysdeps/unix/sysv/linux/fexecve.c
> index 30fa719b56..3bf5de507f 100644
> --- a/sysdeps/unix/sysv/linux/fexecve.c
> +++ b/sysdeps/unix/sysv/linux/fexecve.c
> @@ -19,8 +19,13 @@
> #include <stddef.h>
> #include <stdio.h>
> #include <unistd.h>
> +#include <fcntl.h>
> #include <sys/stat.h>
>
> +#include <sysdep.h>
> +#include <sys/syscall.h>
> +#include <kernel-features.h>
> +
>
> /* Execute the file FD refers to, overlaying the running program image.
> ARGV and ENVP are passed to the new program, as for `execve'. */
> @@ -33,6 +38,15 @@ fexecve (int fd, char *const argv[], char *const envp[])
> return -1;
> }
>
> +#ifdef __NR_execveat
> + INLINE_SYSCALL (execveat, 5, fd, "", argv, envp, AT_EMPTY_PATH);
I would prefer it to use INLINE_SYSCALL_CALL. And since the idea is not to
clobber errno I think we can do:
#ifdef __NR_execvat
INTERNAL_SYSCALL_DECL (err);
int val = INTERNAL_SYSCALL_CALL (execveat, fd, argv, envp, AT_EMPTY_PATH);
if (INTERNAL_SYSCALL_ERROR_P (val, err) != ENOSYS)
return -1;
#endif
> +# ifndef __ASSUME_EXECVEAT
> + if (errno != ENOSYS)
> + return -1;
> +# endif
> +#endif
Do we really need to add another __ASSUME_* that eventually we will need to
cleanup? Can't we just check fo __NR_execvat, call it and if it fails with
ENOSYS use the current code as fallback? The drawback would be that the
fallback code would be mainly dead code for newer kernels.
> +
> +#ifndef __ASSUME_EXECVEAT
> /* We use the /proc filesystem to get the information. If it is not
> mounted we fail. */
> char buf[sizeof "/proc/self/fd/" + sizeof (int) * 3];
> @@ -50,6 +64,7 @@ fexecve (int fd, char *const argv[], char *const envp[])
> save = ENOSYS;
>
> __set_errno (save);
> +#endif
>
> return -1;
> }
> diff --git a/sysdeps/unix/sysv/linux/hppa/kernel-features.h b/sysdeps/unix/sysv/linux/hppa/kernel-features.h
> index 0e73a5c0df..f25a840040 100644
> --- a/sysdeps/unix/sysv/linux/hppa/kernel-features.h
> +++ b/sysdeps/unix/sysv/linux/hppa/kernel-features.h
> @@ -27,3 +27,8 @@
>
> #define __ASSUME_RECV_SYSCALL 1
> #define __ASSUME_SEND_SYSCALL 1
> +
> +/* Support for the execveat syscall was added in 4.0. */
> +#if __LINUX_KERNEL_VERSION < 0x040000
> +# undef __ASSUME_EXECVEAT
> +#endif
> diff --git a/sysdeps/unix/sysv/linux/kernel-features.h b/sysdeps/unix/sysv/linux/kernel-features.h
> index 9495db4fef..2e1fe6597a 100644
> --- a/sysdeps/unix/sysv/linux/kernel-features.h
> +++ b/sysdeps/unix/sysv/linux/kernel-features.h
> @@ -102,3 +102,8 @@
> implementation does not assume the __ASSUME_* and instead use a fallback
> implementation based on p{read,write}v and returning an error for
> non supported flags. */
> +
> +/* Support for the execveat syscall was added in 3.19. */
> +#if __LINUX_KERNEL_VERSION >= 0x031300
> +# define __ASSUME_EXECVEAT 1
> +#endif
> diff --git a/sysdeps/unix/sysv/linux/microblaze/kernel-features.h b/sysdeps/unix/sysv/linux/microblaze/kernel-features.h
> index 0257524777..6575df2a95 100644
> --- a/sysdeps/unix/sysv/linux/microblaze/kernel-features.h
> +++ b/sysdeps/unix/sysv/linux/microblaze/kernel-features.h
> @@ -47,3 +47,8 @@
> #if __LINUX_KERNEL_VERSION < 0x030300
> # undef __ASSUME_SENDMMSG_SYSCALL
> #endif
> +
> +/* Support for the execveat syscall was added in 4.0. */
> +#if __LINUX_KERNEL_VERSION < 0x040000
> +# undef __ASSUME_EXECVEAT
> +#endif
>