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Date: Sat, 29 Mar 2014 17:16:12 +0100
From: "Serge E. Hallyn" <serge@...lyn.com>
To: Jacek Pielaszkiewicz <j.pielaszkie@...sung.com>
Cc: linux-kernel@...r.kernel.org
Subject: Re: Fwd: [SMACK]Problem with user naespace
Quoting Jacek Pielaszkiewicz (j.pielaszkie@...sung.com):
>
> Hi
>
> I have problem with starting lxc containers when SMACK is enabled
> on the host. The issue appears when systemd try start user session in
> the container. In such case systemd reports error that has not
> permissions to set SMACK label. In my test configuration lxc container
> has full separation (all namespaces are enabled - including user namespace).
> The issue is common. The problem is due to lack of permissions of
> the task to write into /proc/self/sttr/current file even the task has
> active CAP_MAC_ADMIN capability. Regarding to may tests the issue is
> connected to user namespace.
>
> I have prepared patch (see below). The patch was tested and created
> on kernel 3.10.
>
> From 1d42d88fccafb7a9fa279588bc827163484a7852 Mon Sep 17 00:00:00 2001
> From: Jacek Pielaszkiewicz <j.pielaszkie@...sung.com>
> Date: Mon, 24 Mar 2014 14:11:58 +0100
> Subject: [PATCH] [PATCH] Enable user namespace in SMACK
>
> SMACK: Enable user namespace
>
> - Bug/Issue:
> The issue has been found when we tried to setup lxc container.
> We tried to setup the container with active all linux namespaces
> (including user namespace). On the host as LSM was enabled SMACK.
>
> We have found that "systemd" was not able to setup user sessiondue
> to lack of permissions to write into /proc/self/attr/currentfile.
>
> We have found general issue that any privileged process with
> enabled CAP_MAC_ADMIN cannot write into /proc/self/attr/currentfile.
>
> - Cause:
> SMACK to check the task capabilities uses capable().
>
> - Solution:
> The fix replaces usage capable() by ns_capable().
>
> Becuase SMACK uses globally defined rules usage ns_capable()
> was limited to places where requested by task operation
> are connected to himself. All operation that modify global SMACK
> rules remain unchanged - SMACK still to test capabilities
> calls capable(). It means that operation on smackfs remain
> unchanged - operation are allowed only by host.
>
> Change-Id: I0bb28fa02943dd7ccb38dda2c8a37dcce2d551b2
> Signed-off-by: Jacek Pielaszkiewicz <j.pielaszkie@...sung.com>
> ---
> security/smack/smack.h | 13 +++++++++++++
> security/smack/smack_access.c | 2 +-
> security/smack/smack_lsm.c | 16 ++++++++--------
> 3 files changed, 22 insertions(+), 9 deletions(-)
>
> diff --git a/security/smack/smack.h b/security/smack/smack.h
> index d072fd3..9f9d5e7 100644
> --- a/security/smack/smack.h
> +++ b/security/smack/smack.h
> @@ -319,6 +319,19 @@ static inline int smack_privileged(int cap)
> }
>
> /*
> + * Is the task privileged and allowed to privileged
> + * by the onlycap rule in user namespace.
> + */
> +static inline int smack_privileged_ns(int cap)
> +{
> + if (!ns_capable(current_user_ns(), cap))
> + return 0;
As I responded on lxc-devel (sorry I had apparently missed this
original mail),
This is an often seen, but very wrong, idiom. This check means
nothing, because any unprivileged user can create a new userns
and pass this check.
You're on the right track, but to do this right you'll need to do a bit
more work. For privilege over an inode, there is inode_capable().
For the network access, check the userns of the struct net owning
the socket. etc.
> + if (smack_onlycap == NULL || smack_onlycap == smk_of_current())
> + return 1;
> + return 0;
> +}
> +
> +/*
> * logging functions
> */
> #define SMACK_AUDIT_DENIED 0x1
> diff --git a/security/smack/smack_access.c b/security/smack/smack_access.c
> index 14293cd..07d25f5 100644
> --- a/security/smack/smack_access.c
> +++ b/security/smack/smack_access.c
> @@ -230,7 +230,7 @@ int smk_curacc(char *obj_label, u32 mode, struct
> smk_audit_info *a)
> /*
> * Allow for priviliged to override policy.
> */
> - if (rc != 0 && smack_privileged(CAP_MAC_OVERRIDE))
> + if (rc != 0 && smack_privileged_ns(CAP_MAC_OVERRIDE))
> rc = 0;
>
> out_audit:
> diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
> index cdbf92b..3cc6842 100644
> --- a/security/smack/smack_lsm.c
> +++ b/security/smack/smack_lsm.c
> @@ -226,7 +226,7 @@ static int smack_syslog(int typefrom_file)
> int rc = 0;
> struct smack_known *skp = smk_of_current();
>
> - if (smack_privileged(CAP_MAC_OVERRIDE))
> + if (smack_privileged_ns(CAP_MAC_OVERRIDE))
> return 0;
>
> if (smack_syslog_label != NULL && smack_syslog_label != skp)
> @@ -842,7 +842,7 @@ static int smack_inode_setxattr(struct dentry
> *dentry, const char *name,
> strcmp(name, XATTR_NAME_SMACKIPOUT) == 0 ||
> strcmp(name, XATTR_NAME_SMACKEXEC) == 0 ||
> strcmp(name, XATTR_NAME_SMACKMMAP) == 0) {
> - if (!smack_privileged(CAP_MAC_ADMIN))
> + if (!smack_privileged_ns(CAP_MAC_ADMIN))
> rc = -EPERM;
> /*
> * check label validity here so import wont fail on
> @@ -852,7 +852,7 @@ static int smack_inode_setxattr(struct dentry
> *dentry, const char *name,
> smk_import(value, size) == NULL)
> rc = -EINVAL;
> } else if (strcmp(name, XATTR_NAME_SMACKTRANSMUTE) == 0) {
> - if (!smack_privileged(CAP_MAC_ADMIN))
> + if (!smack_privileged_ns(CAP_MAC_ADMIN))
> rc = -EPERM;
> if (size != TRANS_TRUE_SIZE ||
> strncmp(value, TRANS_TRUE, TRANS_TRUE_SIZE) != 0)
> @@ -950,7 +950,7 @@ static int smack_inode_removexattr(struct dentry
> *dentry, const char *name)
> strcmp(name, XATTR_NAME_SMACKEXEC) == 0 ||
> strcmp(name, XATTR_NAME_SMACKTRANSMUTE) == 0 ||
> strcmp(name, XATTR_NAME_SMACKMMAP)) {
> - if (!smack_privileged(CAP_MAC_ADMIN))
> + if (!smack_privileged_ns(CAP_MAC_ADMIN))
> rc = -EPERM;
> } else
> rc = cap_inode_removexattr(dentry, name);
> @@ -1342,7 +1342,7 @@ static int smack_file_send_sigiotask(struct
> task_struct *tsk,
> /* we don't log here as rc can be overriden */
> skp = smk_find_entry(file->f_security);
> rc = smk_access(skp, tkp->smk_known, MAY_WRITE, NULL);
> - if (rc != 0 && has_capability(tsk, CAP_MAC_OVERRIDE))
> + if (rc != 0 && has_ns_capability(tsk, current_user_ns(),
> CAP_MAC_OVERRIDE))
> rc = 0;
>
> smk_ad_init(&ad, __func__, LSM_AUDIT_DATA_TASK);
> @@ -2924,7 +2924,7 @@ static int smack_setprocattr(struct task_struct
> *p, char *name,
> if (p != current)
> return -EPERM;
>
> - if (!smack_privileged(CAP_MAC_ADMIN))
> + if (!smack_privileged_ns(CAP_MAC_ADMIN))
> return -EPERM;
>
> if (value == NULL || size == 0 || size >= SMK_LONGLABEL)
> @@ -2980,7 +2980,7 @@ static int smack_unix_stream_connect(struct sock
> *sock,
> smk_ad_setfield_u_net_sk(&ad, other);
> #endif
>
> - if (!smack_privileged(CAP_MAC_OVERRIDE)) {
> + if (!smack_privileged_ns(CAP_MAC_OVERRIDE)) {
> skp = ssp->smk_out;
> rc = smk_access(skp, osp->smk_in, MAY_WRITE, &ad);
> }
> @@ -3018,7 +3018,7 @@ static int smack_unix_may_send(struct socket
> *sock, struct socket *other)
> smk_ad_setfield_u_net_sk(&ad, other->sk);
> #endif
>
> - if (smack_privileged(CAP_MAC_OVERRIDE))
> + if (smack_privileged_ns(CAP_MAC_OVERRIDE))
> return 0;
>
> skp = ssp->smk_out;
> --
> 1.8.3.2
>
>
> I will be grateful for comments
>
>
> Best regards
>
> Jacek Pielaszkiewicz
>
>
>
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