git: be10c0a91015 - main - fexecve(2): allow O_PATH file descriptors opened without O_EXEC

The branch main has been updated by kib:

URL: https://cgit.FreeBSD.org/src/commit/?id=be10c0a910155709dc4e521db3349d50e0440018

commit be10c0a910155709dc4e521db3349d50e0440018
Author:     Konstantin Belousov <kib@FreeBSD.org>
AuthorDate: 2021-11-03 12:51:06 +0000
Commit:     Konstantin Belousov <kib@FreeBSD.org>
CommitDate: 2021-11-03 16:00:42 +0000

    fexecve(2): allow O_PATH file descriptors opened without O_EXEC
    
    This improves compatibility with Linux.
    
    Noted by:       Drew DeVault <sir@cmpwn.com>
    Reviewed by:    markj
    Sponsored by:   The FreeBSD Foundation
    MFC after:      1 week
    Differential revision:  https://reviews.freebsd.org/D32821
---
 lib/libc/sys/open.2     |  3 ---
 sys/kern/kern_descrip.c |  5 +++--
 sys/kern/kern_exec.c    | 13 ++++++++++---
 3 files changed, 13 insertions(+), 8 deletions(-)

diff --git a/lib/libc/sys/open.2 b/lib/libc/sys/open.2
index da42c238a151..f6b061079ddf 100644
--- a/lib/libc/sys/open.2
+++ b/lib/libc/sys/open.2
@@ -334,9 +334,6 @@ but advisory locking is not allowed
 .It Xr close 2
 .It Xr fstat 2
 .It Xr fexecve 2
-requires that
-.Dv O_EXEC
-was also specified at open time
 .It Dv SCM_RIGHTS
 can be passed over a
 .Xr unix 4
diff --git a/sys/kern/kern_descrip.c b/sys/kern/kern_descrip.c
index a7e3785bc672..37d978e96de5 100644
--- a/sys/kern/kern_descrip.c
+++ b/sys/kern/kern_descrip.c
@@ -3213,8 +3213,9 @@ _fget(struct thread *td, int fd, struct file **fpp, int flags,
 			error = EBADF;
 		break;
 	case FEXEC:
-	    	if ((fp->f_flag & (FREAD | FEXEC)) == 0 ||
-		    ((fp->f_flag & FWRITE) != 0))
+		if (fp->f_ops != &path_fileops &&
+		    ((fp->f_flag & (FREAD | FEXEC)) == 0 ||
+		    (fp->f_flag & FWRITE) != 0))
 			error = EBADF;
 		break;
 	case 0:
diff --git a/sys/kern/kern_exec.c b/sys/kern/kern_exec.c
index c5b450b04240..575771346fd1 100644
--- a/sys/kern/kern_exec.c
+++ b/sys/kern/kern_exec.c
@@ -530,13 +530,20 @@ interpret:
 		}
 	} else {
 		AUDIT_ARG_FD(args->fd);
+
 		/*
-		 * Descriptors opened only with O_EXEC or O_RDONLY are allowed.
+		 * If the descriptors was not opened with O_PATH, then
+		 * we require that it was opened with O_EXEC or
+		 * O_RDONLY.  In either case, exec_check_permissions()
+		 * below checks _current_ file access mode regardless
+		 * of the permissions additionally checked at the
+		 * open(2).
 		 */
 		error = fgetvp_exec(td, args->fd, &cap_fexecve_rights,
 		    &newtextvp);
-		if (error)
+		if (error != 0)
 			goto exec_fail;
+
 		if (vn_fullpath(newtextvp, &imgp->execpath,
 		    &imgp->freepath) != 0)
 			imgp->execpath = args->fname;
@@ -881,7 +888,7 @@ interpret:
 
 	/*
 	 * Store the vp for use in kern.proc.pathname.  This vnode was
-	 * referenced by namei() or fgetvp_exec().
+	 * referenced by namei() or by fexecve variant of fname handling.
 	 */
 	oldtextvp = p->p_textvp;
 	p->p_textvp = newtextvp;