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master
lib/libc/sys/execve.2
348 строк
10 KB
jmc
controm terminql -> controlling terminal;
14 окт 2022, 00:37
14 окт 2022, 00:37
a398fd9
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.\" $OpenBSD: execve.2,v 1.58 2022/10/13 21:37:05 jmc Exp $ .\" $NetBSD: execve.2,v 1.9 1995/02/27 12:32:25 cgd Exp $ .\" .\" Copyright (c) 1980, 1991, 1993 .\" The Regents of the University of California. All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. Neither the name of the University nor the names of its contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .\" @(#)execve.2 8.3 (Berkeley) 1/24/94 .\" .Dd $Mdocdate: October 13 2022 $ .Dt EXECVE 2 .Os .Sh NAME .Nm execve .Nd execute a file .Sh SYNOPSIS .In unistd.h .Ft int .Fn execve "const char *path" "char *const argv[]" "char *const envp[]" .Sh DESCRIPTION .Fn execve transforms the calling process into a new process. The new process is constructed from an ordinary file, whose name is pointed to by .Fa path , called the .Em new process file . This file is either an executable object file, or a file of data for an interpreter. An executable object file consists of an identifying header, followed by pages of data representing the initial program (text) and initialized data pages. Additional pages may be specified by the header to be initialized with zero data; see .Xr elf 5 . .Pp An interpreter file begins with a line of the form: .Pp .D1 #! Ar interpreter Op Ar arg .Pp When an interpreter file is passed to .Fn execve , the system instead calls .Fn execve with the specified .Ar interpreter . If the optional .Ar arg is specified, it becomes the first argument to the .Ar interpreter , and the original .Fa path becomes the second argument; otherwise, .Fa path becomes the first argument. The original arguments are shifted over to become the subsequent arguments. The zeroth argument, normally the name of the file being executed, is left unchanged. .Pp The argument .Fa argv is a pointer to a null-terminated array of character pointers to NUL-terminated character strings. These strings construct the argument list to be made available to the new process. At least one non-null argument must be present in the array; by custom, the first element should be the name of the executed program (for example, the last component of .Fa path ) . .Pp The argument .Fa envp is also a pointer to a null-terminated array of character pointers to NUL-terminated strings. A pointer to this array is normally stored in the global variable .Va environ . These strings pass information to the new process that is not directly an argument to the command (see .Xr environ 7 ) . .Pp File descriptors open in the calling process image remain open in the new process image, except for those for which the close-on-exec flag is set (see .Xr close 2 and .Xr fcntl 2 ) . Descriptors that remain open are unaffected by .Fn execve . In the case of a new setuid or setgid executable being executed, if file descriptors 0, 1, or 2 (representing stdin, stdout, and stderr) are currently unallocated, these descriptors will be opened to point to some system file like .Pa /dev/null . The intent is to ensure these descriptors are not unallocated, since many libraries make assumptions about the use of these 3 file descriptors. .Pp Signals set to be ignored in the calling process, with the exception of .Dv SIGCHLD , are set to be ignored in the new process. Other signals are set to default action in the new process image. Blocked signals remain blocked regardless of changes to the signal action. The signal stack is reset to be undefined (see .Xr sigaction 2 for more information). .Pp If the set-user-ID mode bit of the new process image file is set (see .Xr chmod 2 ) , the effective user ID of the new process image is set to the owner ID of the new process image file. If the set-group-ID mode bit of the new process image file is set, the effective group ID of the new process image is set to the group ID of the new process image file. (The effective group ID is the first element of the group list.) The real user ID, real group ID and other group IDs of the new process image remain the same as the calling process image. After any set-user-ID and set-group-ID processing, the effective user ID is recorded as the saved set-user-ID, and the effective group ID is recorded as the saved set-group-ID. These values may be used in changing the effective IDs later (see .Xr setuid 2 ) . The set-user-ID and set-group-ID bits have no effect if the new process image file is located on a file system mounted with the nosuid flag. The process will be started without the new permissions. .Pp The new process also inherits the following attributes from the calling process: .Pp .Bl -tag -width controlling_terminal -offset indent -compact .It process ID see .Xr getpid 2 .It parent process ID see .Xr getppid 2 .It process group ID see .Xr getpgrp 2 .It session ID see .Xr getsid 2 .It access groups see .Xr getgroups 2 .It working directory see .Xr chdir 2 .It root directory see .Xr chroot 2 .It controlling terminal see .Xr termios 4 .It resource usages see .Xr getrusage 2 .It interval timers see .Xr getitimer 2 (unless process image file is setuid or setgid, in which case all timers are disabled) .It resource limits see .Xr getrlimit 2 .It file mode mask see .Xr umask 2 .It signal mask see .Xr sigaction 2 , .Xr sigprocmask 2 .El .Pp When a program is executed as a result of an .Fn execve call, it is entered as follows: .Pp .Dl main(int argc, char **argv, char **envp) .Pp where .Fa argc is the number of elements in .Fa argv (the .Dq arg count ) and .Fa argv points to the array of character pointers to the arguments themselves. .Sh RETURN VALUES As the .Fn execve function overlays the current process image with a new process image, the successful call has no process to return to. If .Fn execve does return to the calling process, an error has occurred; the return value will be \-1 and the global variable .Va errno is set to indicate the error. .Sh ERRORS .Fn execve will fail and return to the calling process if: .Bl -tag -width Er .It Bq Er ENOTDIR A component of the path prefix is not a directory. .It Bq Er ENAMETOOLONG A component of a pathname exceeded .Dv NAME_MAX characters, or an entire pathname (including the terminating NUL) exceeded .Dv PATH_MAX bytes. .It Bq Er ENOENT The new process file does not exist. .It Bq Er ELOOP Too many symbolic links were encountered in translating the pathname. .It Bq Er EACCES Search permission is denied for a component of the path prefix. .It Bq Er EACCES The new process file is not an ordinary file. .It Bq Er EACCES The new process file mode denies execute permission. .It Bq Er EACCES The new process file is on a filesystem mounted with execution disabled .Pf ( Dv MNT_NOEXEC in .In sys/mount.h ) . .It Bq Er EACCES The new process file is marked with .Xr ld 1 .Fl z Cm wxneeded to perform W^X violating operations, but it is located on a file system not allowing such operations, being mounted without the .Xr mount 8 .Fl o Cm wxallowed flag. .It Bq Er EACCES The parent used .Xr pledge 2 to declare an .Va execpromise , and that is not permitted for setuid or setgid images. .It Bq Er ENOEXEC The new process file has the appropriate access permission, but has an invalid magic number in its header. .It Bq Er ETXTBSY The new process file is a pure procedure (shared text) file that is currently open for writing by some process. .It Bq Er ENOMEM The new process requires more virtual memory than is allowed by the imposed maximum .Pq Xr getrlimit 2 . .It Bq Er E2BIG The number of bytes in the new process's argument list is larger than the system-imposed limit. The limit in the system as released is 524288 bytes .Pq Dv ARG_MAX . .It Bq Er EFAULT The new process file is not as long as indicated by the size values in its header. .It Bq Er EFAULT .Fa path , .Fa argv , or .Fa envp point to an illegal address. .It Bq Er EINVAL .Fa argv did not contain at least one element. .It Bq Er EIO An I/O error occurred while reading from the file system. .It Bq Er ENFILE During startup of an .Ar interpreter , the system file table was found to be full. .El .Sh SEE ALSO .Xr _exit 2 , .Xr fork 2 , .Xr execl 3 , .Xr exit 3 , .Xr elf 5 , .Xr environ 7 .Sh STANDARDS The .Fn execve function is expected to conform to .St -p1003.1-2008 . .Sh HISTORY The predecessor of these functions, the former .Fn exec system call, first appeared in .At v1 . The .Fn execve function first appeared in .At v7 . .Sh CAVEATS If a program is .Em setuid to a non-superuser, but is executed when the real .Em uid is .Dq root , then the process has some of the powers of a superuser as well. .Pp .St -p1003.1-2008 permits .Nm to leave .Dv SIGCHLD as ignored in the new process; portable programs cannot rely on .Nm resetting it to the default disposition.