linuxolator: Add compat.linux.setid_allowed knob

PR:	21463
Reported by:	kris
Reviewed by:	dchagin
Tested by:	trasz
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Differential Revision:	https://reviews.freebsd.org/D28154

7 files changed, 33 insertions, 1 deletions

diff --git a/share/man/man4/linux.4 b/share/man/man4/linux.4
index 23bc0c26f7f9..b2d36158c622 100644
--- a/share/man/man4/linux.4
+++ b/share/man/man4/linux.4
@@ -24,7 +24,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd July 5, 2020
+.Dd May 6, 2021
 .Dt LINUX 4
 .Os
 .Sh NAME
@@ -130,6 +130,18 @@ From a user perspective, this makes
 .Va SIGINFO
 work for Linux executables.
 Defaults to 0.
+.It Va compat.linux.setid_allowed
+Disable handling of set-user-ID and set-group-ID mode bits for the new
+process image file when image is to be executed under Linux ABI.
+When set, new Linux images always use credentials of the program
+that issued
+.Xr execve 2
+call, regardless of the image file mode.
+.Pp
+This might be reasonable or even required, because
+.Fx
+does not emulate Linux environment completely, and missed features
+could become holes.
 .El
 .Sh FILES
 .Bl -tag -width /compat/linux/dev/shm -compact
diff --git a/sys/amd64/linux/linux_sysvec.c b/sys/amd64/linux/linux_sysvec.c
index 02225e63072d..3eab9126f192 100644
--- a/sys/amd64/linux/linux_sysvec.c
+++ b/sys/amd64/linux/linux_sysvec.c
@@ -764,6 +764,7 @@ struct sysentvec elf_linux_sysvec = {
 	.sv_onexec	= linux_on_exec,
 	.sv_onexit	= linux_on_exit,
 	.sv_ontdexit	= linux_thread_dtor,
+	.sv_setid_allowed = &linux_setid_allowed_query,
 };
 
 static void
diff --git a/sys/amd64/linux32/linux32_sysvec.c b/sys/amd64/linux32/linux32_sysvec.c
index 05354803cf03..b950c00eba1d 100644
--- a/sys/amd64/linux32/linux32_sysvec.c
+++ b/sys/amd64/linux32/linux32_sysvec.c
@@ -931,6 +931,7 @@ struct sysentvec elf_linux_sysvec = {
 	.sv_onexec	= linux_on_exec,
 	.sv_onexit	= linux_on_exit,
 	.sv_ontdexit	= linux_thread_dtor,
+	.sv_setid_allowed = &linux_setid_allowed_query,
 };
 
 static void
diff --git a/sys/arm64/linux/linux_sysvec.c b/sys/arm64/linux/linux_sysvec.c
index 365cb9fc386a..57abdc6fd691 100644
--- a/sys/arm64/linux/linux_sysvec.c
+++ b/sys/arm64/linux/linux_sysvec.c
@@ -443,6 +443,7 @@ struct sysentvec elf_linux_sysvec = {
 	.sv_onexec	= linux_on_exec,
 	.sv_onexit	= linux_on_exit,
 	.sv_ontdexit	= linux_thread_dtor,
+	.sv_setid_allowed = &linux_setid_allowed_query,
 };
 
 static void
diff --git a/sys/compat/linux/linux_mib.c b/sys/compat/linux/linux_mib.c
index cc4207f74a39..3a6627df9abd 100644
--- a/sys/compat/linux/linux_mib.c
+++ b/sys/compat/linux/linux_mib.c
@@ -99,6 +99,18 @@ int linux_use_emul_path = 1;
 SYSCTL_INT(_compat_linux, OID_AUTO, use_emul_path, CTLFLAG_RWTUN,
     &linux_use_emul_path, 0, "Use linux.compat.emul_path");
 
+static bool linux_setid_allowed = true;
+SYSCTL_BOOL(_compat_linux, OID_AUTO, setid_allowed, CTLFLAG_RWTUN,
+    &linux_setid_allowed, 0,
+    "Allow setuid/setgid on execve of Linux binary");
+
+bool
+linux_setid_allowed_query(struct thread *td __unused,
+    struct image_params *imgp __unused)
+{
+	return (linux_setid_allowed);
+}
+
 static int	linux_set_osname(struct thread *td, char *osname);
 static int	linux_set_osrelease(struct thread *td, char *osrelease);
 static int	linux_set_oss_version(struct thread *td, int oss_version);
diff --git a/sys/compat/linux/linux_mib.h b/sys/compat/linux/linux_mib.h
index c4d3d1e83f7e..adf71cb65401 100644
--- a/sys/compat/linux/linux_mib.h
+++ b/sys/compat/linux/linux_mib.h
@@ -71,4 +71,7 @@ extern int linux_ignore_ip_recverr;
 extern int linux_preserve_vstatus;
 extern bool linux_map_sched_prio;
 
+struct image_params;
+bool linux_setid_allowed_query(struct thread *td, struct image_params *imgp);
+
 #endif /* _LINUX_MIB_H_ */
diff --git a/sys/i386/linux/linux_sysvec.c b/sys/i386/linux/linux_sysvec.c
index 0e6ad4b5c137..9cc1a723ab55 100644
--- a/sys/i386/linux/linux_sysvec.c
+++ b/sys/i386/linux/linux_sysvec.c
@@ -871,6 +871,7 @@ struct sysentvec linux_sysvec = {
 	.sv_onexec	= linux_on_exec,
 	.sv_onexit	= linux_on_exit,
 	.sv_ontdexit	= linux_thread_dtor,
+	.sv_setid_allowed = &linux_setid_allowed_query,
 };
 INIT_SYSENTVEC(aout_sysvec, &linux_sysvec);
 
@@ -908,6 +909,7 @@ struct sysentvec elf_linux_sysvec = {
 	.sv_onexec	= linux_on_exec,
 	.sv_onexit	= linux_on_exit,
 	.sv_ontdexit	= linux_thread_dtor,
+	.sv_setid_allowed = &linux_setid_allowed_query,
 };
 
 static void