Manpage of FEXECVE
FEXECVESection: Linux Programmer's Manual (3)
NAMEfexecve - execute program specified via file descriptor
#include <unistd.h>int fexecve(int fd, char *const argv, char *const envp);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
- Since glibc 2.10:
- _POSIX_C_SOURCE >= 200809L
- Before glibc 2.10:
DESCRIPTIONfexecve() 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 fdmust be opened read-only, and the caller must have permission to execute the file that it refers to.
RETURN VALUEA successful call to fexecve() never returns. On error, the function does return, with a result value of -1, and errnois set appropriately.
ERRORSErrors are as for execve(2), with the following additions:
- fdis not a valid file descriptor, or argvis NULL, or envpis NULL.
- The /procfilesystem could not be accessed.
VERSIONSfexecve() is implemented since glibc 2.3.2.
ATTRIBUTESFor an explanation of the terms used in this section, see attributes(7).
CONFORMING TOPOSIX.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.
NOTESOn Linux, fexecve() is implemented using the proc(5) filesystem, so /procneeds to be mounted and available at the time of the call.
The idea behind fexecve() is to allow the caller to verify (checksum) the 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 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.of an executable before executing it. Simply opening the file, checksumming the , and then doing an
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.)
BUGSIf fdrefers 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, fdhas already been closed because of the close-on-exec flag. Thus, the close-on-exec flag can't be set on fdif it refers to a script, leading to the problems described in NOTES.
SEE ALSOexecve(2), execveat(2)
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