Quoting Max Kellermann ([email protected]):
> Add two LSM hooks for limiting access to the proc file system.
>
> security_proc_task() defines the visibility of tasks in /proc.
>
> security_proc_generic() lets the LSM define who will see "generic"
> proc entries (see fs/proc/generic.c).
>
> This patch attempts to unify duplicated code found in modules like
> Linux VServer.
Are you aware of the pid namespace patches currently in -mm?
If your use for the task hiding hooks is to emulate virtual
servers as with vserver/openvz, the pid namespaces should fill
your need.
-serge
> Signed-off-by: Max Kellermann <[email protected]>
>
> ---
> fs/proc/base.c | 9 +++++++++
> fs/proc/generic.c | 15 +++++++++++++++
> include/linux/security.h | 46 ++++++++++++++++++++++++++++++++++++++++++++++
> security/Kconfig | 8 ++++++++
> security/dummy.c | 16 ++++++++++++++++
> 5 files changed, 94 insertions(+), 0 deletions(-)
>
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index 19489b0..a6ebe2d 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -2317,6 +2317,10 @@ int proc_pid_readdir(struct file * filp, void * dirent, filldir_t filldir)
> put_task_struct(task), task = next_tgid(tgid + 1)) {
> tgid = task->pid;
> filp->f_pos = tgid + TGID_OFFSET;
> +#ifdef CONFIG_SECURITY_PROC
> + if (security_proc_task(task) != 0)
> + continue;
> +#endif
> if (proc_pid_fill_cache(filp, dirent, filldir, task, tgid) < 0) {
> put_task_struct(task);
> goto out;
> @@ -2453,6 +2457,11 @@ static struct dentry *proc_task_lookup(struct inode *dir, struct dentry * dentry
> goto out;
> if (leader->tgid != task->tgid)
> goto out_drop_task;
> +#ifdef CONFIG_SECURITY_PROC
> + result = ERR_PTR(security_proc_task(task));
> + if (IS_ERR(result))
> + goto out_drop_task;
> +#endif
>
> result = proc_task_instantiate(dir, dentry, task, NULL);
> out_drop_task:
> diff --git a/fs/proc/generic.c b/fs/proc/generic.c
> index b5e7155..7b17ec3 100644
> --- a/fs/proc/generic.c
> +++ b/fs/proc/generic.c
> @@ -21,6 +21,9 @@
> #include <linux/bitops.h>
> #include <linux/spinlock.h>
> #include <linux/completion.h>
> +#ifdef CONFIG_SECURITY_PROC
> +#include <linux/security.h>
> +#endif
> #include <asm/uaccess.h>
>
> #include "internal.h"
> @@ -400,6 +403,11 @@ struct dentry *proc_lookup(struct inode * dir, struct dentry *dentry, struct nam
> unsigned int ino = de->low_ino;
>
> de_get(de);
> +#ifdef CONFIG_SECURITY_PROC
> + error = security_proc_generic(de);
> + if (error != 0)
> + break;
> +#endif
> spin_unlock(&proc_subdir_lock);
> error = -EINVAL;
> inode = proc_get_inode(dir->i_sb, ino, de);
> @@ -483,6 +491,10 @@ int proc_readdir(struct file * filp,
>
> /* filldir passes info to user space */
> de_get(de);
> +#ifdef CONFIG_SECURITY_PROC
> + if (security_proc_generic(de) != 0)
> + goto skip;
> +#endif
> spin_unlock(&proc_subdir_lock);
> if (filldir(dirent, de->name, de->namelen, filp->f_pos,
> de->low_ino, de->mode >> 12) < 0) {
> @@ -490,6 +502,9 @@ int proc_readdir(struct file * filp,
> goto out;
> }
> spin_lock(&proc_subdir_lock);
> +#ifdef CONFIG_SECURITY_PROC
> + skip:
> +#endif
> filp->f_pos++;
> next = de->next;
> de_put(de);
> diff --git a/include/linux/security.h b/include/linux/security.h
> index 1a15526..3fbeacf 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -68,6 +68,10 @@ struct xfrm_policy;
> struct xfrm_state;
> struct xfrm_user_sec_ctx;
>
> +#ifdef CONFIG_SECURITY_PROC
> +struct proc_dir_entry;
> +#endif
> +
> extern int cap_netlink_send(struct sock *sk, struct sk_buff *skb);
> extern int cap_netlink_recv(struct sk_buff *skb, int cap);
>
> @@ -915,6 +919,17 @@ struct request_sock;
> * Return 1 if permission granted, 0 if permission denied and -ve it the
> * normal permissions model should be effected.
> *
> + * Security hooks affecting proc visibility
> + *
> + * @proc_task:
> + * Determines whether a task is visible.
> + * @task the requested task
> + * Return 0 if task is visible, -ENOENT if not, or -errno on other errors
> + * @proc_generic:
> + * Determines whether a generic proc entry is visible
> + * @de the requested proc_dir_entry structure
> + * Return 0 if entry is visible, -ENOENT if not, or -errno on other errors
> + *
> * Security hooks affecting all System V IPC operations.
> *
> * @ipc_permission:
> @@ -1399,6 +1414,11 @@ struct security_operations {
>
> #endif /* CONFIG_KEYS */
>
> + #ifdef CONFIG_SECURITY_PROC
> + int (*proc_task)(struct task_struct *task);
> + int (*proc_generic)(struct proc_dir_entry *de);
> + #endif
> +
> };
>
> /* global variables */
> @@ -3314,5 +3334,31 @@ static inline int security_key_permission(key_ref_t key_ref,
> #endif
> #endif /* CONFIG_KEYS */
>
> +#ifdef CONFIG_SECURITY_PROC
> +#ifdef CONFIG_SECURITY
> +static inline int security_proc_task(struct task_struct *task)
> +{
> + return security_ops->proc_task(task);
> +}
> +
> +static inline int security_proc_generic(struct proc_dir_entry *de)
> +{
> + return security_ops->proc_generic(de);
> +}
> +
> +#else
> +
> +static inline int security_proc_task(struct task_struct *task)
> +{
> + return 0;
> +}
> +
> +static inline int security_proc_generic(struct proc_dir_entry *de)
> +{
> + return 0;
> +}
> +#endif
> +#endif
> +
> #endif /* ! __LINUX_SECURITY_H */
>
> diff --git a/security/Kconfig b/security/Kconfig
> index 460e5c9..bd6ad4b 100644
> --- a/security/Kconfig
> +++ b/security/Kconfig
> @@ -73,6 +73,14 @@ config SECURITY_NETWORK_XFRM
> IPSec.
> If you are unsure how to answer this question, answer N.
>
> +config SECURITY_PROC
> + bool "/proc Security Hooks"
> + depends on PROC_FS && SECURITY
> + help
> + This enables the /proc security hooks.
> + These allow an LSM to hide nodes in the proc filesystem.
> + If you are unsure how to answer this question, answer N.
> +
> config SECURITY_CAPABILITIES
> tristate "Default Linux Capabilities"
> depends on SECURITY
> diff --git a/security/dummy.c b/security/dummy.c
> index 853ec22..3ec57be 100644
> --- a/security/dummy.c
> +++ b/security/dummy.c
> @@ -949,6 +949,18 @@ static inline int dummy_key_permission(key_ref_t key_ref,
> }
> #endif /* CONFIG_KEYS */
>
> +#ifdef CONFIG_SECURITY_PROC
> +static int dummy_proc_task(struct task_struct *task)
> +{
> + return 0;
> +}
> +
> +static int dummy_proc_generic(struct proc_dir_entry *de)
> +{
> + return 0;
> +}
> +#endif
> +
> struct security_operations dummy_security_ops;
>
> #define set_to_dummy_if_null(ops, function) \
> @@ -1131,6 +1143,10 @@ void security_fixup_ops (struct security_operations *ops)
> set_to_dummy_if_null(ops, key_free);
> set_to_dummy_if_null(ops, key_permission);
> #endif /* CONFIG_KEYS */
> +#ifdef CONFIG_SECURITY_PROC
> + set_to_dummy_if_null(ops, proc_task);
> + set_to_dummy_if_null(ops, proc_generic);
> +#endif
>
> }
>
> -
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