git: 773fa8cd136a - main - execve: disallow argc == 0

The branch main has been updated by kevans:

URL: https://cgit.FreeBSD.org/src/commit/?id=773fa8cd136a5775241c3e3a70f1997633ebeedf

commit 773fa8cd136a5775241c3e3a70f1997633ebeedf
Author:     Kyle Evans <kevans@FreeBSD.org>
AuthorDate: 2022-01-25 22:47:23 +0000
Commit:     Kyle Evans <kevans@FreeBSD.org>
CommitDate: 2022-01-26 19:40:27 +0000

    execve: disallow argc == 0
    
    The manpage has contained the following verbiage on the matter for just
    under 31 years:
    
    "At least one argument must be present in the array"
    
    Previous to this version, it had been prefaced with the weakening phrase
    "By convention."
    
    Carry through and document it the rest of the way.  Allowing argc == 0
    has been a source of security issues in the past, and it's hard to
    imagine a valid use-case for allowing it.  Toss back EINVAL if we ended
    up not copying in any args for *execve().
    
    The manpage change can be considered "Obtained from: OpenBSD"
    
    Reviewed by:    emaste, kib, markj (all previous version)
    Differential Revision:  https://reviews.freebsd.org/D34045
---
 lib/libc/sys/execve.2 | 5 ++++-
 sys/kern/kern_exec.c  | 6 ++++++
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/lib/libc/sys/execve.2 b/lib/libc/sys/execve.2
index a8f5aa14854b..1abadba13d91 100644
--- a/lib/libc/sys/execve.2
+++ b/lib/libc/sys/execve.2
@@ -28,7 +28,7 @@
 .\"     @(#)execve.2	8.5 (Berkeley) 6/1/94
 .\" $FreeBSD$
 .\"
-.Dd March 30, 2020
+.Dd January 26, 2022
 .Dt EXECVE 2
 .Os
 .Sh NAME
@@ -273,6 +273,9 @@ Search permission is denied for a component of the path prefix.
 The new process file is not an ordinary file.
 .It Bq Er EACCES
 The new process file mode denies execute permission.
+.It Bq Er EINVAL
+.Fa argv
+did not contain at least one element.
 .It Bq Er ENOEXEC
 The new process file has the appropriate access
 permission, but has an invalid magic number in its header.
diff --git a/sys/kern/kern_exec.c b/sys/kern/kern_exec.c
index 0494b73fc405..303c145689ae 100644
--- a/sys/kern/kern_exec.c
+++ b/sys/kern/kern_exec.c
@@ -356,6 +356,12 @@ kern_execve(struct thread *td, struct image_args *args, struct mac *mac_p,
 	    exec_args_get_begin_envv(args) - args->begin_argv);
 	AUDIT_ARG_ENVV(exec_args_get_begin_envv(args), args->envc,
 	    args->endp - exec_args_get_begin_envv(args));
+
+	/* Must have at least one argument. */
+	if (args->argc == 0) {
+		exec_free_args(args);
+		return (EINVAL);
+	}
 	return (do_execve(td, args, mac_p, oldvmspace));
 }