fexecve - execute program specified via file descriptor

       For an explanation of the terms used in this section, see attributes(7).
       ┌─────────────────────────────────────────────────────────────────────────────┬───────────────┬─────────┐
       │ Interface                                                                   │ Attribute     │ Value   │
       ├─────────────────────────────────────────────────────────────────────────────┼───────────────┼─────────┤
       │ fexecve()                                                                   │ Thread safety │ MT-Safe │
       └─────────────────────────────────────────────────────────────────────────────┴───────────────┴─────────┘

       If  fd  refers  to  a  script (i.e., it is an executable text file that names a script interpreter with a
       first line that begins with the characters #!)  and the close-on-exec flag has  been  set  for  fd,  then
       fexecve()  fails with the error ENOENT.  This error occurs because, by the time the script interpreter is
       executed, fd has already been closed because of the close-on-exec flag.   Thus,  the  close-on-exec  flag
       can't be set on fd if it refers to a script, leading to the problems described in NOTES.

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 (O_RDONLY) or with the O_PATH flag and the caller must have permission to execute the file that
       it refers to.

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

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

       ENOENT The close-on-exec flag is set on fd, and fd refers to a script.  See BUGS.

       ENOSYS The  kernel  does  not  provide the execveat(2) system call, and the /proc filesystem could not be
              accessed.

       glibc 2.3.2.

       On Linux with glibc versions 2.26 and earlier, fexecve() is implemented using the proc(5) filesystem,  so
       /proc  needs  to  be  mounted and available at the time of the call.  Since glibc 2.27, if the underlying
       kernel supports the execveat(2) system call, then fexecve() is implemented using that system  call,  with
       the benefit that /proc does not need to be mounted.

       Standard C library (libc, -lc)

       fexecve - execute program specified via file descriptor

       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.

       The natural idiom when using fexecve() is to  set  the  close-on-exec  flag  on  fd,  so  that  the  file
       descriptor  does  not  leak  through  to  the program that is executed.  This approach is natural for two
       reasons.  First, it prevents file  descriptors  being  consumed  unnecessarily.   (The  executed  program
       normally  has  no  need of a file descriptor that refers to the program itself.)  Second, if fexecve() is
       used recursively, employing the close-on-exec flag prevents the file  descriptor  exhaustion  that  would
       result from the fact that each step in the recursion would cause one more file descriptor to be passed to
       the new program.  (But see BUGS.)

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

execve(2), execveat(2)

Linux man-pages 6.9.1                              2024-05-02                                         fexecve(3)

       POSIX.1-2008.

#include<unistd.h>intfexecve(intfd,char*constargv[],char*constenvp[]);

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

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