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Date: Sat, 1 Mar 2008 19:41:04 -0800 (PST)
From: Casey Schaufler <casey@...aufler-ca.com>
To: "Ahmed S. Darwish" <darwish.07@...il.com>,
Casey Schaufler <casey@...aufler-ca.com>
Cc: Adrian Bunk <bunk@...nel.org>, Chris Wright <chrisw@...s-sol.org>,
Stephen Smalley <sds@...ho.nsa.gov>,
James Morris <jmorris@...ei.org>,
Eric Paris <eparis@...isplace.org>,
Alexey Dobriyan <adobriyan@...ru>,
LKML <linux-kernel@...r.kernel.org>,
LSM-ML <linux-security-module@...r.kernel.org>,
Anrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH -v2 -mm] LSM: Add security= boot parameter
--- "Ahmed S. Darwish" <darwish.07@...il.com> wrote:
> Hi!,
>
> Add the security= boot parameter. This is done to avoid LSM
> registration clashes in case of more than one bult-in module.
>
> User can choose a security module to enable at boot. If no
> security= boot parameter is specified, only the first LSM
> asking for registration will be loaded. An invalid security
> module name will be treated as if no module has been chosen.
>
> LSM modules must check now if they are allowed to register
> by calling security_module_enable(ops) first. Modify SELinux
> and SMACK to do so.
>
> Signed-off-by: Ahmed S. Darwish <darwish.07@...il.com>
> ---
>
> I'll send a similar patch for 2.6.25 if no more concerns for
> the patch exist.
>
> Adrian, Casey, Does this one have any more issues ?
>
> Documentation/kernel-parameters.txt | 6 ++++
> include/linux/security.h | 12 +++++++++
> security/dummy.c | 3 +-
> security/security.c | 47
> +++++++++++++++++++++++++++++++++++-
> security/selinux/hooks.c | 5 +++
> security/smack/smack_lsm.c | 7 +++++
>
> 6 files changed, 77 insertions(+), 3 deletions(-)
>
> diff --git a/Documentation/kernel-parameters.txt
> b/Documentation/kernel-parameters.txt
> index c64dfd7..85044e8 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -374,6 +374,12 @@ and is between 256 and 4096 characters. It is defined in
> the file
> possible to determine what the correct size should be.
> This option provides an override for these situations.
>
> + security= [SECURITY] Choose a security module to enable at boot.
> + If this boot parameter is not specified, only the first
> + security module asking for security registration will be
> + loaded. An invalid security module name will be treated
> + as if no module has been chosen.
> +
Yes, this is better.
> capability.disable=
> [SECURITY] Disable capabilities. This would normally
> be used only if an alternative security model is to be
> diff --git a/include/linux/security.h b/include/linux/security.h
> index a33fd03..416afcf 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -42,6 +42,9 @@
>
> extern unsigned securebits;
>
> +/* Maximum number of letters for an LSM name string */
> +#define SECURITY_NAME_MAX 10
> +
> struct ctl_table;
>
> /*
> @@ -117,6 +120,12 @@ struct request_sock;
> /**
> * struct security_operations - main security structure
> *
> + * Security module identifier.
> + *
> + * @name:
> + * A string that acts as unique identifeir for the LSM with max number
> + * of characters = SECURITY_NAME_MAX.
> + *
> * Security hooks for program execution operations.
> *
> * @bprm_alloc_security:
> @@ -1218,6 +1227,8 @@ struct request_sock;
> * This is the main security structure.
> */
> struct security_operations {
> + char name[SECURITY_NAME_MAX + 1];
> +
> int (*ptrace) (struct task_struct * parent, struct task_struct * child);
> int (*capget) (struct task_struct * target,
> kernel_cap_t * effective,
> @@ -1477,6 +1488,7 @@ struct security_operations {
>
> /* prototypes */
> extern int security_init (void);
> +extern int security_module_enable(struct security_operations *ops);
> extern int register_security (struct security_operations *ops);
> extern int mod_reg_security (const char *name, struct security_operations
> *ops);
> extern struct dentry *securityfs_create_file(const char *name, mode_t mode,
> diff --git a/security/dummy.c b/security/dummy.c
> index 6a0056b..7cb999c 100644
> --- a/security/dummy.c
> +++ b/security/dummy.c
> @@ -986,7 +986,7 @@ static int dummy_key_getsecurity(struct key *key, char
> **_buffer)
>
> #endif /* CONFIG_KEYS */
>
> -struct security_operations dummy_security_ops;
> +struct security_operations dummy_security_ops = { "dummy" };
>
> #define set_to_dummy_if_null(ops, function) \
> do { \
> @@ -999,6 +999,7 @@ struct security_operations dummy_security_ops;
>
> void security_fixup_ops (struct security_operations *ops)
> {
> + BUG_ON(!ops->name);
> set_to_dummy_if_null(ops, ptrace);
> set_to_dummy_if_null(ops, capget);
> set_to_dummy_if_null(ops, capset_check);
> diff --git a/security/security.c b/security/security.c
> index 3e75b90..261d2e4 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -17,6 +17,9 @@
> #include <linux/kernel.h>
> #include <linux/security.h>
>
> +/* Boot-time LSM user choice */
> +static char chosen_lsm[SECURITY_NAME_MAX + 1];
> +static atomic_t security_ops_registered = ATOMIC_INIT(0);
>
> /* things that live in dummy.c */
> extern struct security_operations dummy_security_ops;
> @@ -67,13 +70,54 @@ int __init security_init(void)
> return 0;
> }
>
> +/* Save user chosen LSM */
> +static int __init choose_lsm(char *str)
> +{
> + if (strlen(str) > SECURITY_NAME_MAX) {
> + printk(KERN_INFO "Security: LSM name length extends possible"
> + "limit.\n");
> + printk(KERN_INFO "Security: Ignoring passed security= "
> + "parameter.\n");
> + return 0;
> + }
> +
> + strncpy(chosen_lsm, str, SECURITY_NAME_MAX);
> + return 1;
> +}
> +__setup("security=", choose_lsm);
> +
> +/**
> + * security_module_enable - Load given security module on boot ?
> + * @ops: a pointer to the struct security_operations that is to be checked.
> + *
> + * Return true if:
> + * -The passed LSM is the one chosen by user at boot time,
> + * -or user didsn't specify a specific LSM and we're the first to ask
> + * for registeration permissoin.
> + * Otherwise, return false.
> + */
> +int security_module_enable(struct security_operations *ops)
> +{
> + if (!ops || !ops->name)
> + return 0;
> +
> + if (!*chosen_lsm && !atomic_read(&security_ops_registered))
> + return 1;
> +
> + if (!strncmp(ops->name, chosen_lsm, SECURITY_NAME_MAX))
> + return 1;
> +
> + return 0;
> +}
> +
> /**
> * register_security - registers a security framework with the kernel
> * @ops: a pointer to the struct security_options that is to be registered
> *
> * This function is to allow a security module to register itself with the
> * kernel security subsystem. Some rudimentary checking is done on the @ops
> - * value passed to this function.
> + * value passed to this function. You'll need to check first if your LSM
> + * is allowed to register by calling security_module_enable(@ops).
> *
> * If there is already a security module registered with the kernel,
> * an error will be returned. Otherwise 0 is returned on success.
> @@ -90,6 +134,7 @@ int register_security(struct security_operations *ops)
> return -EAGAIN;
>
> security_ops = ops;
> + atomic_inc(&security_ops_registered);
>
> return 0;
> }
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index f42ebfc..fe30d2b 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -5233,6 +5233,8 @@ static int selinux_key_getsecurity(struct key *key,
> char **_buffer)
> #endif
>
> static struct security_operations selinux_ops = {
> + .name = "selinux",
> +
> .ptrace = selinux_ptrace,
> .capget = selinux_capget,
> .capset_check = selinux_capset_check,
> @@ -5420,7 +5422,8 @@ static __init int selinux_init(void)
> {
> struct task_security_struct *tsec;
>
> - if (!selinux_enabled) {
> + if (!selinux_enabled || !security_module_enable(&selinux_ops)) {
> + selinux_enabled = 0;
> printk(KERN_INFO "SELinux: Disabled at boot.\n");
How about "SELinux: Not enabled because LSM %s is already enabled.\n"
> return 0;
> }
> diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
> index 2b5d6f7..3fc8c6e 100644
> --- a/security/smack/smack_lsm.c
> +++ b/security/smack/smack_lsm.c
> @@ -2358,6 +2358,8 @@ static void smack_release_secctx(char *secdata, u32
> seclen)
> }
>
> static struct security_operations smack_ops = {
> + .name = "smack",
> +
> .ptrace = smack_ptrace,
> .capget = cap_capget,
> .capset_check = cap_capset_check,
> @@ -2485,6 +2487,11 @@ static struct security_operations smack_ops = {
> */
> static __init int smack_init(void)
> {
> + if (!security_module_enable(&smack_ops)) {
> + printk(KERN_INFO "Smack: Disabled at boot.\n");
How about "Smack: Not enabled because LSM %s is already enabled.\n"
> + return 0;
> + }
> +
> printk(KERN_INFO "Smack: Initializing.\n");
>
> /*
>
> --
>
> "Better to light a candle, than curse the darkness"
>
> Ahmed S. Darwish
> Homepage: http://darwish.07.googlepages.com
> Blog: http://darwish-07.blogspot.com
>
>
>
Casey Schaufler
casey@...aufler-ca.com
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