FEXECVE(3)                          Linux Programmer's Manual                          FEXECVE(3)



NAME
       fexecve - execute program specified via file descriptor

SYNOPSIS
       #include <unistd.h>

       int fexecve(int fd, char *const argv[], char *const envp[]);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       fexecve():
           Since glibc 2.10:
               _XOPEN_SOURCE >= 700 || _POSIX_C_SOURCE >= 200809L
           Before glibc 2.10:
               _GNU_SOURCE

DESCRIPTION
       fexecve()  performs  the  same  task as execve(2), with the difference that the file to be
       executed is specified via a file descriptor, fd, rather than via  a  pathname.   The  file
       descriptor fd must be opened read-only, and the caller must have permission to execute the
       file that it refers to.

RETURN VALUE
       A successful call to fexecve() never returns.  On error, the function does return, with  a
       result value of -1, and errno is set appropriately.

ERRORS
       Errors are as for execve(2), with the following additions:

       EINVAL fd is not a valid file descriptor, or argv is NULL, or envp is NULL.

       ENOSYS The /proc filesystem could not be accessed.

VERSIONS
       fexecve() is implemented since glibc 2.3.2.

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.

NOTES
       On Linux, fexecve() is implemented using the proc(5) filesystem,  so  /proc  needs  to  be
       mounted and available at the time of the call.

       If  fd  is  a  file descriptor that refers to an interpreter script and has been marked as
       close-on-exec (see the discussion of the FD_CLOEXEC in fcntl(2)), fexecve() will  fail  to
       execute  the  script, since, by the time the script interpreter tries to access the script
       file, fd has already been closed.

       The idea behind 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 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).  fexecve() does not mitigate the problem that the contents
       of  a  file could be changed between the checksumming and the call to fexecve(); for that,
       the solution is to ensure that the permissions on the file prevent it from being  modified
       by malicious users.

SEE ALSO
       execve(2)

COLOPHON
       This  page  is  part of release 3.74 of the Linux man-pages project.  A description of the
       project, information about reporting bugs, and the latest version of  this  page,  can  be
       found at http://www.kernel.org/doc/man-pages/.



Linux                                       2014-04-20                                 FEXECVE(3)