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Add a new jail permission, allow.read_msgbuf. When true, jailed processes

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can see the dmesg buffer (this is the current behavior).  When false (the
new default), dmesg will be unavailable to jailed users, whether root or
not.

The security.bsd.unprivileged_read_msgbuf sysctl still works as before,
controlling system-wide whether non-root users can see the buffer.

PR:		211580
Submitted by:	bz
Approved by:	re@ (kib@)
MFC after:	3 days
This commit is contained in:
Jamie Gritton 2018-10-17 16:11:43 +00:00
parent eb144aa007
commit b19d66fd5a
5 changed files with 39 additions and 12 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
sys/kern/kern_jail.c
View File

@ -193,6 +193,7 @@ static struct bool_flags pr_flag_allow[NBBY * NBPW] = {
{"allow.mlock", "allow.nomlock", PR_ALLOW_MLOCK},
{"allow.reserved_ports", "allow.noreserved_ports",
PR_ALLOW_RESERVED_PORTS},
{"allow.read_msgbuf", "allow.noread_msgbuf", PR_ALLOW_READ_MSGBUF},
};
const size_t pr_flag_allow_size = sizeof(pr_flag_allow);
@ -3350,6 +3351,15 @@ prison_priv_check(struct ucred *cred, int priv)
case PRIV_PROC_SETLOGINCLASS:
return (0);
/*
* Do not allow a process inside a jail read the kernel
* message buffer unless explicitly permitted.
*/
case PRIV_MSGBUF:
if (cred->cr_prison->pr_allow & PR_ALLOW_READ_MSGBUF)
return (0);
return (EPERM);
default:
/*
* In all remaining cases, deny the privilege request. This
@ -3770,6 +3780,8 @@ SYSCTL_JAIL_PARAM(_allow, mlock, CTLTYPE_INT | CTLFLAG_RW,
"B", "Jail may lock (unlock) physical pages in memory");
SYSCTL_JAIL_PARAM(_allow, reserved_ports, CTLTYPE_INT | CTLFLAG_RW,
"B", "Jail may bind sockets to reserved ports");
SYSCTL_JAIL_PARAM(_allow, read_msgbuf, CTLTYPE_INT | CTLFLAG_RW,
"B", "Jail may read the kernel message buffer");
SYSCTL_JAIL_PARAM_SUBNODE(allow, mount, "Jail mount/unmount permission flags");
SYSCTL_JAIL_PARAM(_allow_mount, , CTLTYPE_INT | CTLFLAG_RW,

16
sys/kern/kern_priv.c
View File

@ -62,6 +62,11 @@ static int unprivileged_mlock = 1;
SYSCTL_INT(_security_bsd, OID_AUTO, unprivileged_mlock, CTLFLAG_RWTUN,
&unprivileged_mlock, 0, "Allow non-root users to call mlock(2)");
static int unprivileged_read_msgbuf = 1;
SYSCTL_INT(_security_bsd, OID_AUTO, unprivileged_read_msgbuf,
CTLFLAG_RW, &unprivileged_read_msgbuf, 0,
"Unprivileged processes may read the kernel message buffer");
SDT_PROVIDER_DEFINE(priv);
SDT_PROBE_DEFINE1(priv, kernel, priv_check, priv__ok, "int");
SDT_PROBE_DEFINE1(priv, kernel, priv_check, priv__err, "int");
@ -109,6 +114,17 @@ priv_check_cred(struct ucred *cred, int priv, int flags)
}
}
if (unprivileged_read_msgbuf) {
/*
* Allow an unprivileged user to read the kernel message
* buffer.
*/
if (priv == PRIV_MSGBUF) {
error = 0;
goto out;
}
}
/*
* Having determined if privilege is restricted by various policies,
* now determine if privilege is granted. At this point, any policy

7
sys/kern/subr_prf.c
View File

@ -1053,11 +1053,6 @@ msgbufinit(void *ptr, int size)
oldp = msgbufp;
}
static int unprivileged_read_msgbuf = 1;
SYSCTL_INT(_security_bsd, OID_AUTO, unprivileged_read_msgbuf,
CTLFLAG_RW, &unprivileged_read_msgbuf, 0,
"Unprivileged processes may read the kernel message buffer");
/* Sysctls for accessing/clearing the msgbuf */
static int
sysctl_kern_msgbuf(SYSCTL_HANDLER_ARGS)
@ -1066,11 +1061,9 @@ sysctl_kern_msgbuf(SYSCTL_HANDLER_ARGS)
u_int seq;
int error, len;
if (!unprivileged_read_msgbuf) {
error = priv_check(req->td, PRIV_MSGBUF);
if (error)
return (error);
}
/* Read the whole buffer, one chunk at a time. */
mtx_lock(&msgbuf_lock);

3
sys/sys/jail.h
View File

@ -228,9 +228,10 @@ struct prison_racct {
#define PR_ALLOW_QUOTAS 0x00000020
#define PR_ALLOW_SOCKET_AF 0x00000040
#define PR_ALLOW_MLOCK 0x00000080
#define PR_ALLOW_READ_MSGBUF 0x00000100
#define PR_ALLOW_RESERVED_PORTS 0x00008000
#define PR_ALLOW_KMEM_ACCESS 0x00010000 /* reserved, not used yet */
#define PR_ALLOW_ALL_STATIC 0x000180ff
#define PR_ALLOW_ALL_STATIC 0x000181ff
/*
* OSD methods

7
usr.sbin/jail/jail.8
View File

@ -25,7 +25,7 @@
.\"
.\" $FreeBSD$
.\"
.Dd August 20, 2018
.Dd October 17, 2018
.Dt JAIL 8
.Os
.Sh NAME
@ -549,6 +549,11 @@ option.
The jail root may administer quotas on the jail's filesystem(s).
This includes filesystems that the jail may share with other jails or
with non-jailed parts of the system.
.It Va allow.read_msgbuf
Jailed users may read the kernel message buffer.
If the
.Va security.bsd.unprivileged_read_msgbuf
MIB entry is zero, this will be restricted to to root user.
.It Va allow.socket_af
Sockets within a jail are normally restricted to IPv4, IPv6, local
(UNIX), and route. This allows access to other protocol stacks that