Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1396173 > unrolled thread

[PATCH 0/2] Quiet noisy LSM denial when accessing net sysctl

Back to article view | Back to linux.kernel

Contents

  [PATCH 0/2] Quiet noisy LSM denial when accessing net sysctl Tyler Hicks <tyhicks@canonical.com> - 2016-05-07 01:10 +0200
    [PATCH 1/2] kernel: Add noaudit variant of ns_capable() Tyler Hicks <tyhicks@canonical.com> - 2016-05-07 01:10 +0200
      Re: [PATCH 1/2] kernel: Add noaudit variant of ns_capable() Serge Hallyn <serge.hallyn@ubuntu.com> - 2016-05-09 06:30 +0200
    [PATCH 2/2] net: Use ns_capable_noaudit() when determining net sysctl permissions Tyler Hicks <tyhicks@canonical.com> - 2016-05-07 01:10 +0200
      Re: [PATCH 2/2] net: Use ns_capable_noaudit() when determining net  sysctl permissions Serge Hallyn <serge.hallyn@ubuntu.com> - 2016-05-09 06:30 +0200
    Re: [PATCH 0/2] Quiet noisy LSM denial when accessing net sysctl David Miller <davem@davemloft.net> - 2016-05-09 06:00 +0200

#1396173 — [PATCH 0/2] Quiet noisy LSM denial when accessing net sysctl

This pair of patches does away with what I believe is a useless denial
audit message when a privileged process initially accesses a net sysctl.

The bug was first discovered when running Go applications under AppArmor
confinement. It can be triggered like so:

  $ echo "profile test { file, }" | sudo apparmor_parser -rq

Once the profile is loaded, invoke Go as root under confinement:

  $ sudo aa-exec -p test -- go version
  go version go1.6.1 linux/amd64

Here's the denial:

  audit: type=1400 audit(1462575436.832:29): apparmor="DENIED" operation="capable" profile="test" pid=1157 comm="go" capability=12  capname="net_admin"

The reproducer in minimal form is:

  $ sudo aa-exec -p test -- cat /proc/sys/net/core/somaxconn
  128

The denial:

  audit: type=1400 audit(1462575670.000:29): apparmor="DENIED" operation="capable" profile="test" pid=1161 comm="cat" capability=12  capname="net_admin"

Thanks!

Tyler

[toc] | [next] | [standalone]

#1396175 — [PATCH 1/2] kernel: Add noaudit variant of ns_capable()

When checking the current cred for a capability in a specific user
namespace, it isn't always desirable to have the LSMs audit the check.
This patch adds a noaudit variant of ns_capable() for when those
situations arise.

The common logic between ns_capable() and the new ns_capable_noaudit()
is moved into a single, shared function to keep duplicated code to a
minimum and ease maintainability.

Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
---
 include/linux/capability.h |  5 +++++
 kernel/capability.c        | 46 ++++++++++++++++++++++++++++++++++++----------
 2 files changed, 41 insertions(+), 10 deletions(-)

diff --git a/include/linux/capability.h b/include/linux/capability.h
index 00690ff..5f3c63d 100644
--- a/include/linux/capability.h
+++ b/include/linux/capability.h
@@ -206,6 +206,7 @@ extern bool has_ns_capability_noaudit(struct task_struct *t,
 				      struct user_namespace *ns, int cap);
 extern bool capable(int cap);
 extern bool ns_capable(struct user_namespace *ns, int cap);
+extern bool ns_capable_noaudit(struct user_namespace *ns, int cap);
 #else
 static inline bool has_capability(struct task_struct *t, int cap)
 {
@@ -233,6 +234,10 @@ static inline bool ns_capable(struct user_namespace *ns, int cap)
 {
 	return true;
 }
+static inline bool ns_capable_noaudit(struct user_namespace *ns, int cap)
+{
+	return true;
+}
 #endif /* CONFIG_MULTIUSER */
 extern bool capable_wrt_inode_uidgid(const struct inode *inode, int cap);
 extern bool file_ns_capable(const struct file *file, struct user_namespace *ns, int cap);
diff --git a/kernel/capability.c b/kernel/capability.c
index 45432b5..00411c8 100644
--- a/kernel/capability.c
+++ b/kernel/capability.c
@@ -361,6 +361,24 @@ bool has_capability_noaudit(struct task_struct *t, int cap)
 	return has_ns_capability_noaudit(t, &init_user_ns, cap);
 }
 
+static bool ns_capable_common(struct user_namespace *ns, int cap, bool audit)
+{
+	int capable;
+
+	if (unlikely(!cap_valid(cap))) {
+		pr_crit("capable() called with invalid cap=%u\n", cap);
+		BUG();
+	}
+
+	capable = audit ? security_capable(current_cred(), ns, cap) :
+			  security_capable_noaudit(current_cred(), ns, cap);
+	if (capable == 0) {
+		current->flags |= PF_SUPERPRIV;
+		return true;
+	}
+	return false;
+}
+
 /**
  * ns_capable - Determine if the current task has a superior capability in effect
  * @ns:  The usernamespace we want the capability in
@@ -374,19 +392,27 @@ bool has_capability_noaudit(struct task_struct *t, int cap)
  */
 bool ns_capable(struct user_namespace *ns, int cap)
 {
-	if (unlikely(!cap_valid(cap))) {
-		pr_crit("capable() called with invalid cap=%u\n", cap);
-		BUG();
-	}
-
-	if (security_capable(current_cred(), ns, cap) == 0) {
-		current->flags |= PF_SUPERPRIV;
-		return true;
-	}
-	return false;
+	return ns_capable_common(ns, cap, true);
 }
 EXPORT_SYMBOL(ns_capable);
 
+/**
+ * ns_capable_noaudit - Determine if the current task has a superior capability
+ * (unaudited) in effect
+ * @ns:  The usernamespace we want the capability in
+ * @cap: The capability to be tested for
+ *
+ * Return true if the current task has the given superior capability currently
+ * available for use, false if not.
+ *
+ * This sets PF_SUPERPRIV on the task if the capability is available on the
+ * assumption that it's about to be used.
+ */
+bool ns_capable_noaudit(struct user_namespace *ns, int cap)
+{
+	return ns_capable_common(ns, cap, false);
+}
+EXPORT_SYMBOL(ns_capable_noaudit);
 
 /**
  * capable - Determine if the current task has a superior capability in effect
-- 
2.7.4

[toc] | [prev] | [next] | [standalone]

#1396581 — Re: [PATCH 1/2] kernel: Add noaudit variant of ns_capable()

Quoting Tyler Hicks (tyhicks@canonical.com):
> When checking the current cred for a capability in a specific user
> namespace, it isn't always desirable to have the LSMs audit the check.
> This patch adds a noaudit variant of ns_capable() for when those
> situations arise.
> 
> The common logic between ns_capable() and the new ns_capable_noaudit()
> is moved into a single, shared function to keep duplicated code to a
> minimum and ease maintainability.
> 
> Signed-off-by: Tyler Hicks <tyhicks@canonical.com>

Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com>

> ---
>  include/linux/capability.h |  5 +++++
>  kernel/capability.c        | 46 ++++++++++++++++++++++++++++++++++++----------
>  2 files changed, 41 insertions(+), 10 deletions(-)
> 
> diff --git a/include/linux/capability.h b/include/linux/capability.h
> index 00690ff..5f3c63d 100644
> --- a/include/linux/capability.h
> +++ b/include/linux/capability.h
> @@ -206,6 +206,7 @@ extern bool has_ns_capability_noaudit(struct task_struct *t,
>  				      struct user_namespace *ns, int cap);
>  extern bool capable(int cap);
>  extern bool ns_capable(struct user_namespace *ns, int cap);
> +extern bool ns_capable_noaudit(struct user_namespace *ns, int cap);
>  #else
>  static inline bool has_capability(struct task_struct *t, int cap)
>  {
> @@ -233,6 +234,10 @@ static inline bool ns_capable(struct user_namespace *ns, int cap)
>  {
>  	return true;
>  }
> +static inline bool ns_capable_noaudit(struct user_namespace *ns, int cap)
> +{
> +	return true;
> +}
>  #endif /* CONFIG_MULTIUSER */
>  extern bool capable_wrt_inode_uidgid(const struct inode *inode, int cap);
>  extern bool file_ns_capable(const struct file *file, struct user_namespace *ns, int cap);
> diff --git a/kernel/capability.c b/kernel/capability.c
> index 45432b5..00411c8 100644
> --- a/kernel/capability.c
> +++ b/kernel/capability.c
> @@ -361,6 +361,24 @@ bool has_capability_noaudit(struct task_struct *t, int cap)
>  	return has_ns_capability_noaudit(t, &init_user_ns, cap);
>  }
>  
> +static bool ns_capable_common(struct user_namespace *ns, int cap, bool audit)
> +{
> +	int capable;
> +
> +	if (unlikely(!cap_valid(cap))) {
> +		pr_crit("capable() called with invalid cap=%u\n", cap);
> +		BUG();
> +	}
> +
> +	capable = audit ? security_capable(current_cred(), ns, cap) :
> +			  security_capable_noaudit(current_cred(), ns, cap);
> +	if (capable == 0) {
> +		current->flags |= PF_SUPERPRIV;
> +		return true;
> +	}
> +	return false;
> +}
> +
>  /**
>   * ns_capable - Determine if the current task has a superior capability in effect
>   * @ns:  The usernamespace we want the capability in
> @@ -374,19 +392,27 @@ bool has_capability_noaudit(struct task_struct *t, int cap)
>   */
>  bool ns_capable(struct user_namespace *ns, int cap)
>  {
> -	if (unlikely(!cap_valid(cap))) {
> -		pr_crit("capable() called with invalid cap=%u\n", cap);
> -		BUG();
> -	}
> -
> -	if (security_capable(current_cred(), ns, cap) == 0) {
> -		current->flags |= PF_SUPERPRIV;
> -		return true;
> -	}
> -	return false;
> +	return ns_capable_common(ns, cap, true);
>  }
>  EXPORT_SYMBOL(ns_capable);
>  
> +/**
> + * ns_capable_noaudit - Determine if the current task has a superior capability
> + * (unaudited) in effect
> + * @ns:  The usernamespace we want the capability in
> + * @cap: The capability to be tested for
> + *
> + * Return true if the current task has the given superior capability currently
> + * available for use, false if not.
> + *
> + * This sets PF_SUPERPRIV on the task if the capability is available on the
> + * assumption that it's about to be used.
> + */
> +bool ns_capable_noaudit(struct user_namespace *ns, int cap)
> +{
> +	return ns_capable_common(ns, cap, false);
> +}
> +EXPORT_SYMBOL(ns_capable_noaudit);
>  
>  /**
>   * capable - Determine if the current task has a superior capability in effect
> -- 
> 2.7.4
> 

[toc] | [prev] | [next] | [standalone]

#1396177 — [PATCH 2/2] net: Use ns_capable_noaudit() when determining net sysctl permissions

The capability check should not be audited since it is only being used
to determine the inode permissions. A failed check does not indicate a
violation of security policy but, when an LSM is enabled, a denial audit
message was being generated.

The denial audit message caused confusion for some application authors
because root-running Go applications always triggered the denial. To
prevent this confusion, the capability check in net_ctl_permissions() is
switched to the noaudit variant.

BugLink: https://launchpad.net/bugs/1465724

Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
---
 net/sysctl_net.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/sysctl_net.c b/net/sysctl_net.c
index ed98c1f..46a71c7 100644
--- a/net/sysctl_net.c
+++ b/net/sysctl_net.c
@@ -46,7 +46,7 @@ static int net_ctl_permissions(struct ctl_table_header *head,
 	kgid_t root_gid = make_kgid(net->user_ns, 0);
 
 	/* Allow network administrator to have same access as root. */
-	if (ns_capable(net->user_ns, CAP_NET_ADMIN) ||
+	if (ns_capable_noaudit(net->user_ns, CAP_NET_ADMIN) ||
 	    uid_eq(root_uid, current_euid())) {
 		int mode = (table->mode >> 6) & 7;
 		return (mode << 6) | (mode << 3) | mode;
-- 
2.7.4

[toc] | [prev] | [next] | [standalone]

#1396579 — Re: [PATCH 2/2] net: Use ns_capable_noaudit() when determining net sysctl permissions

Quoting Tyler Hicks (tyhicks@canonical.com):
> The capability check should not be audited since it is only being used
> to determine the inode permissions. A failed check does not indicate a
> violation of security policy but, when an LSM is enabled, a denial audit
> message was being generated.
> 
> The denial audit message caused confusion for some application authors
> because root-running Go applications always triggered the denial. To
> prevent this confusion, the capability check in net_ctl_permissions() is
> switched to the noaudit variant.
> 
> BugLink: https://launchpad.net/bugs/1465724
> 
> Signed-off-by: Tyler Hicks <tyhicks@canonical.com>

Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com>

> ---
>  net/sysctl_net.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/sysctl_net.c b/net/sysctl_net.c
> index ed98c1f..46a71c7 100644
> --- a/net/sysctl_net.c
> +++ b/net/sysctl_net.c
> @@ -46,7 +46,7 @@ static int net_ctl_permissions(struct ctl_table_header *head,
>  	kgid_t root_gid = make_kgid(net->user_ns, 0);
>  
>  	/* Allow network administrator to have same access as root. */
> -	if (ns_capable(net->user_ns, CAP_NET_ADMIN) ||
> +	if (ns_capable_noaudit(net->user_ns, CAP_NET_ADMIN) ||
>  	    uid_eq(root_uid, current_euid())) {
>  		int mode = (table->mode >> 6) & 7;
>  		return (mode << 6) | (mode << 3) | mode;
> -- 
> 2.7.4
> 

[toc] | [prev] | [next] | [standalone]

#1396571

From: Tyler Hicks <tyhicks@canonical.com>
Date: Fri,  6 May 2016 18:04:12 -0500

> This pair of patches does away with what I believe is a useless denial
> audit message when a privileged process initially accesses a net sysctl.

The LSM folks can apply this if they agree with you.

[toc] | [prev] | [standalone]

Back to top | Article view | linux.kernel

csiph-web