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diff --git a/lib/libsys/chmod.2 b/lib/libsys/chmod.2
--- a/lib/libsys/chmod.2
+++ b/lib/libsys/chmod.2
@@ -25,7 +25,7 @@
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
-.Dd March 30, 2021
+.Dd October 31, 2024
.Dt CHMOD 2
.Os
.Sh NAME
@@ -214,6 +214,13 @@
by protecting set-user-id (set-group-id) files
from remaining set-user-id (set-group-id) if they are modified,
at the expense of a degree of compatibility.
+.Pp
+While it is normally an error to invoke
+.Fn fchmod
+on a socket, it is possible to do so on
+.Dv AF_LOCAL
+sockets before they are bound to a file name; see
+.Xr unix 4 .
.Sh RETURN VALUES
.Rv -std
.Sh ERRORS
diff --git a/share/man/man4/unix.4 b/share/man/man4/unix.4
--- a/share/man/man4/unix.4
+++ b/share/man/man4/unix.4
@@ -25,7 +25,7 @@
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
-.Dd February 1, 2022
+.Dd October 31, 2024
.Dt UNIX 4
.Os
.Sh NAME
@@ -77,6 +77,15 @@
.Xr unlink 2
must be used to remove the file.
.Pp
+Prior to binding a socket,
+.Xr fchmod 2
+can be used to set the permissions of the socket file.
+This avoids the race that would otherwise occur between creation of the file
+and a subsequent call to
+.Xr chmod 2 .
+Once the socket is bound to a file name, the permissions of the file can not be
+changed this way.
+.Pp
The length of
.Ux Ns -domain
address, required by
@@ -441,6 +450,7 @@
.Sh SEE ALSO
.Xr connect 2 ,
.Xr dup 2 ,
+.Xr fchmod 2 ,
.Xr fcntl 2 ,
.Xr getsockopt 2 ,
.Xr listen 2 ,
diff --git a/sys/kern/sys_socket.c b/sys/kern/sys_socket.c
--- a/sys/kern/sys_socket.c
+++ b/sys/kern/sys_socket.c
@@ -90,6 +90,7 @@
extern fo_kqfilter_t soo_kqfilter;
static fo_stat_t soo_stat;
static fo_close_t soo_close;
+static fo_chmod_t soo_chmod;
static fo_fill_kinfo_t soo_fill_kinfo;
static fo_aio_queue_t soo_aio_queue;
@@ -104,7 +105,7 @@
.fo_kqfilter = soo_kqfilter,
.fo_stat = soo_stat,
.fo_close = soo_close,
- .fo_chmod = invfo_chmod,
+ .fo_chmod = soo_chmod,
.fo_chown = invfo_chown,
.fo_sendfile = invfo_sendfile,
.fo_fill_kinfo = soo_fill_kinfo,
@@ -353,6 +354,20 @@
return (error);
}
+static int
+soo_chmod(struct file *fp, mode_t mode, struct ucred *cred, struct thread *td)
+{
+ struct socket *so;
+ int error;
+
+ so = fp->f_data;
+ if (so->so_proto->pr_chmod != NULL)
+ error = so->so_proto->pr_chmod(so, mode, cred, td);
+ else
+ error = EINVAL;
+ return (error);
+}
+
static int
soo_fill_kinfo(struct file *fp, struct kinfo_file *kif, struct filedesc *fdp)
{
diff --git a/sys/kern/uipc_usrreq.c b/sys/kern/uipc_usrreq.c
--- a/sys/kern/uipc_usrreq.c
+++ b/sys/kern/uipc_usrreq.c
@@ -484,6 +484,7 @@
unp->unp_socket = so;
so->so_pcb = unp;
refcount_init(&unp->unp_refcount, 1);
+ unp->unp_mode = ACCESSPERMS;
if ((locked = UNP_LINK_WOWNED()) == false)
UNP_LINK_WLOCK();
@@ -526,6 +527,7 @@
struct mount *mp;
cap_rights_t rights;
char *buf;
+ mode_t mode;
if (nam->sa_family != AF_UNIX)
return (EAFNOSUPPORT);
@@ -558,6 +560,7 @@
return (EALREADY);
}
unp->unp_flags |= UNP_BINDING;
+ mode = unp->unp_mode & ~td->td_proc->p_pd->pd_cmask;
UNP_PCB_UNLOCK(unp);
buf = malloc(namelen + 1, M_TEMP, M_WAITOK);
@@ -590,7 +593,7 @@
}
VATTR_NULL(&vattr);
vattr.va_type = VSOCK;
- vattr.va_mode = (ACCESSPERMS & ~td->td_proc->p_pd->pd_cmask);
+ vattr.va_mode = mode;
#ifdef MAC
error = mac_vnode_check_create(td->td_ucred, nd.ni_dvp, &nd.ni_cnd,
&vattr);
@@ -702,6 +705,27 @@
}
}
+static int
+uipc_chmod(struct socket *so, mode_t mode, struct ucred *cred __unused,
+ struct thread *td __unused)
+{
+ struct unpcb *unp;
+ int error;
+
+ if ((mode & ~ACCESSPERMS) != 0)
+ return (EINVAL);
+
+ error = 0;
+ unp = sotounpcb(so);
+ UNP_PCB_LOCK(unp);
+ if (unp->unp_vnode != NULL || (unp->unp_flags & UNP_BINDING) != 0)
+ error = EINVAL;
+ else
+ unp->unp_mode = mode;
+ UNP_PCB_UNLOCK(unp);
+ return (error);
+}
+
static int
uipc_connect2(struct socket *so1, struct socket *so2)
{
@@ -3357,6 +3381,7 @@
.pr_sockaddr = uipc_sockaddr,
.pr_soreceive = soreceive_generic,
.pr_close = uipc_close,
+ .pr_chmod = uipc_chmod,
};
static struct protosw dgramproto = {
@@ -3380,6 +3405,7 @@
.pr_sockaddr = uipc_sockaddr,
.pr_soreceive = uipc_soreceive_dgram,
.pr_close = uipc_close,
+ .pr_chmod = uipc_chmod,
};
static struct protosw seqpacketproto = {
@@ -3411,6 +3437,7 @@
.pr_sockaddr = uipc_sockaddr,
.pr_soreceive = soreceive_generic, /* XXX: or...? */
.pr_close = uipc_close,
+ .pr_chmod = uipc_chmod,
};
static struct domain localdomain = {
diff --git a/sys/sys/protosw.h b/sys/sys/protosw.h
--- a/sys/sys/protosw.h
+++ b/sys/sys/protosw.h
@@ -32,6 +32,8 @@
#ifndef _SYS_PROTOSW_H_
#define _SYS_PROTOSW_H_
+#include <sys/_types.h>
+
/* Forward declare these structures referenced from prototypes below. */
struct kaiocb;
struct mbuf;
@@ -100,6 +102,8 @@
typedef int pr_connectat_t(int, struct socket *, struct sockaddr *,
struct thread *);
typedef int pr_aio_queue_t(struct socket *, struct kaiocb *);
+typedef int pr_chmod_t(struct socket *, __mode_t, struct ucred *,
+ struct thread *);
struct protosw {
short pr_type; /* socket type used for */
@@ -139,6 +143,7 @@
pr_sense_t *pr_sense; /* stat(2) */
pr_sosetlabel_t *pr_sosetlabel; /* MAC, XXXGL: remove */
pr_setsbopt_t *pr_setsbopt; /* Socket buffer ioctls */
+ pr_chmod_t *pr_chmod; /* fchmod(2) */
};
/*#endif*/
diff --git a/sys/sys/unpcb.h b/sys/sys/unpcb.h
--- a/sys/sys/unpcb.h
+++ b/sys/sys/unpcb.h
@@ -93,6 +93,7 @@
u_int unp_msgcount; /* (g) references from message queue */
u_int unp_gcrefs; /* (g) garbage collector refcount */
ino_t unp_ino; /* (g) fake inode number */
+ mode_t unp_mode; /* (g) initial pre-bind() mode */
LIST_ENTRY(unpcb) unp_dead; /* (g) link in dead list */
} __aligned(CACHE_LINE_SIZE);
diff --git a/tests/sys/kern/unix_dgram.c b/tests/sys/kern/unix_dgram.c
--- a/tests/sys/kern/unix_dgram.c
+++ b/tests/sys/kern/unix_dgram.c
@@ -25,13 +25,15 @@
* SUCH DAMAGE.
*/
-#include <sys/time.h>
#include <sys/event.h>
#include <sys/ioctl.h>
#include <sys/select.h>
#include <sys/socket.h>
+#include <sys/stat.h>
#include <sys/sysctl.h>
+#include <sys/time.h>
#include <sys/un.h>
+
#include <aio.h>
#include <errno.h>
#include <fcntl.h>
@@ -391,12 +393,49 @@
ATF_REQUIRE(close(sd) == 0);
}
+ATF_TC_WITHOUT_HEAD(fchmod);
+ATF_TC_BODY(fchmod, tc)
+{
+ struct stat sb;
+ struct sockaddr_un sun;
+ int error, sd;
+
+ memset(&sun, 0, sizeof(sun));
+ sun.sun_len = sizeof(sun);
+ sun.sun_family = AF_UNIX;
+ strlcpy(sun.sun_path, "sock", sizeof(sun.sun_path));
+
+ sd = socket(PF_UNIX, SOCK_DGRAM, 0);
+ ATF_REQUIRE(sd != -1);
+
+ error = fchmod(sd, 0600 | S_ISUID);
+ ATF_REQUIRE_ERRNO(EINVAL, error == -1);
+
+ umask(0022);
+ error = fchmod(sd, 0766);
+ ATF_REQUIRE(error == 0);
+
+ error = bind(sd, (struct sockaddr *)&sun, sizeof(sun));
+ ATF_REQUIRE(error == 0);
+
+ error = stat(sun.sun_path, &sb);
+ ATF_REQUIRE(error == 0);
+ ATF_REQUIRE_MSG((sb.st_mode & 0777) == 0744,
+ "sb.st_mode = %o", sb.st_mode);
+
+ error = fchmod(sd, 0666);
+ ATF_REQUIRE_ERRNO(EINVAL, error == -1);
+
+ ATF_REQUIRE(close(sd) == 0);
+}
+
ATF_TP_ADD_TCS(tp)
{
ATF_TP_ADD_TC(tp, basic);
ATF_TP_ADD_TC(tp, one2many);
ATF_TP_ADD_TC(tp, event);
ATF_TP_ADD_TC(tp, selfgetpeername);
+ ATF_TP_ADD_TC(tp, fchmod);
return (atf_no_error());
}

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