FEXECVE
Section: Linux Programmer's Manual (3)
Updated: 2014-04-20
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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)
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- VERSIONS
-
- CONFORMING TO
-
- NOTES
-
- SEE ALSO
-
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Time: 02:55:12 GMT, September 18, 2014