(split) LDP: Update original to LDP v3.65

[linuxjm/LDP_man-pages.git] / original / man3 / fexecve.3

diff --git a/original/man3/fexecve.3 b/original/man3/fexecve.3
index 99b18ba..b4dd1d6 100644 (file)
--- a/original/man3/fexecve.3
+++ b/original/man3/fexecve.3
@@ -1,7 +1,6 @@
-.\" Hey Emacs! This file is -*- nroff -*- source.
-.\"
 .\" Copyright (c) 2006, Michael Kerrisk
 .\"
+.\" %%%LICENSE_START(VERBATIM)
 .\" Permission is granted to make and distribute verbatim copies of this
 .\" manual provided the copyright notice and this permission notice are
 .\" preserved on all copies.
@@ -21,8 +20,9 @@
 .\"
 .\" Formatted or processed versions of this manual, if unaccompanied by
 .\" the source, must acknowledge the copyright and authors of this work.
+.\" %%%LICENSE_END
 .\"
-.TH FEXECVE 3 2010-09-15 "Linux" "Linux Programmer's Manual"
+.TH FEXECVE 3 2014-04-20 "Linux" "Linux Programmer's Manual"
 .SH NAME
 fexecve \- execute program specified via file descriptor
 .SH SYNOPSIS
@@ -64,11 +64,11 @@ must be opened read-only,
 and the caller must have permission to execute the file that it refers to.
 .\" POSIX.1-2008 specifies the O_EXEC flag for open as an alternative,
 .\" but Linux doesn't support this flag yet.
-.SH "RETURN VALUE"
+.SH RETURN VALUE
 A successful call to
 .BR fexecve ()
 never returns.
-On error, the function returns, with a result value of \-1, and
+On error, the function does return, with a result value of \-1, and
 .I errno
 is set appropriately.
 .SH ERRORS
@@ -87,21 +87,60 @@ is NULL.
 .B ENOSYS
 The
 .I /proc
-file system could not be accessed.
+filesystem could not be accessed.
 .SH VERSIONS
 .BR fexecve ()
 is implemented since glibc 2.3.2.
-.SH "CONFORMING TO"
+.SH CONFORMING TO
 POSIX.1-2008.
 This function is not specified in POSIX.1-2001,
 and is not widely available on other systems.
+It is specified in POSIX.1-2008.
 .SH NOTES
 On Linux,
 .BR fexecve ()
 is implemented using the
 .BR proc (5)
-file system, so
+filesystem, so
 .I /proc
 needs to be mounted and available at the time of the call.
-.SH "SEE ALSO"
+
+If
+.I fd
+is a file descriptor that refers to an interpreter script
+and has been marked as close-on-exec (see the discussion of the
+.BR FD_CLOEXEC
+in
+.BR fcntl (2)),
+.BR fexecve ()
+will fail to execute the script, since,
+by the time the script interpreter tries to access the script file,
+.I fd
+has already been closed.
+
+The idea behind
+.BR fexecve ()
+is to allow the caller to verify (checksum) the contents of
+an executable before executing it.
+Simply opening the file, checksumming the contents, and then doing an
+.BR execve (2)
+would not suffice, since, between the two steps, the filename,
+or a directory prefix of the pathname, could have been exchanged
+(by, for example, modifying the target of a symbolic link).
+.BR fexecve ()
+does not mitigate the problem that the
+.I contents
+of a file could be changed between the checksumming and the call to
+.BR fexecve ();
+for that, the solution is to ensure that the permissions on the file
+prevent it from being modified by malicious users.
+.SH SEE ALSO
 .BR execve (2)
+.SH COLOPHON
+This page is part of release 3.65 of the Linux
+.I man-pages
+project.
+A description of the project,
+and information about reporting bugs,
+can be found at
+\%http://www.kernel.org/doc/man\-pages/.