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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
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Linux 2014-04-20 FEXECVE(3)
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