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fs,security: Add a security blob to nameidata

The function current_nameidata_security(struct inode *) can be used to
retrieve a blob's pointer address tied to the inode being walk through.
This enable to follow a path lookup and know where an inode access come
from. This is needed for the Landlock LSM to be able to restrict access
to file path.

The LSM hook nameidata_free_security(struct inode *) is called before
freeing the associated nameidata.

Signed-off-by: Mickaël Salaün <mic@digikod.net>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Casey Schaufler <casey@schaufler-ca.com>
Cc: James Morris <jmorris@namei.org>
Cc: John Johansen <john.johansen@canonical.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Paul Moore <paul@paul-moore.com>
Cc: "Serge E. Hallyn" <serge@hallyn.com>
Cc: Stephen Smalley <sds@tycho.nsa.gov>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: linux-fsdevel@vger.kernel.org
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l0kod committed Feb 27, 2018
1 parent 7d72637 commit 45cfee44b53e309274fa2388911b39ca1837cb38
Showing with 73 additions and 1 deletion.
  1. +39 −0 fs/namei.c
  2. +7 −0 include/linux/lsm_hooks.h
  3. +13 −1 include/linux/namei.h
  4. +7 −0 include/linux/security.h
  5. +7 −0 security/security.c
@@ -505,6 +505,9 @@ struct nameidata {
struct inode *link_inode;
unsigned root_seq;
int dfd;
#ifdef CONFIG_SECURITY
struct nameidata_lookup lookup;
#endif
} __randomize_layout;

static void set_nameidata(struct nameidata *p, int dfd, struct filename *name)
@@ -515,13 +518,17 @@ static void set_nameidata(struct nameidata *p, int dfd, struct filename *name)
p->name = name;
p->total_link_count = old ? old->total_link_count : 0;
p->saved = old;
#ifdef CONFIG_SECURITY
p->lookup.security = NULL;
#endif
current->nameidata = p;
}

static void restore_nameidata(void)
{
struct nameidata *now = current->nameidata, *old = now->saved;

security_nameidata_put_lookup(&now->lookup, now->inode);
current->nameidata = old;
if (old)
old->total_link_count = now->total_link_count;
@@ -549,6 +556,27 @@ static int __nd_alloc_stack(struct nameidata *nd)
return 0;
}

#ifdef CONFIG_SECURITY
/**
* current_nameidata_lookup - get the state of the current path walk
*
* @inode: inode associated to the path walk
*
* Used by LSM modules for access restriction based on path walk. The LSM is in
* charge of the lookup->security blob allocation and management. The hook
* security_nameidata_put_lookup() will be called after the path walk end.
*
* Return ERR_PTR(-ENOENT) if there is no match.
*/
struct nameidata_lookup *current_nameidata_lookup(const struct inode *inode)
{
if (!current->nameidata || current->nameidata->inode != inode)
return ERR_PTR(-ENOENT);
return &current->nameidata->lookup;
}
EXPORT_SYMBOL(current_nameidata_lookup);
#endif

/**
* path_connected - Verify that a path->dentry is below path->mnt.mnt_root
* @path: nameidate to verify
@@ -2009,6 +2037,13 @@ static inline u64 hash_name(const void *salt, const char *name)

#endif

static inline void refresh_lookup(struct nameidata *nd)
{
#ifdef CONFIG_SECURITY
nd->lookup.type = nd->last_type;
#endif
}

/*
* Name resolution.
* This is the basic name resolution function, turning a pathname into
@@ -2025,6 +2060,8 @@ static int link_path_walk(const char *name, struct nameidata *nd)
name++;
if (!*name)
return 0;
/* be ready for may_lookup() */
refresh_lookup(nd);

/* At this point we know we have a real path component. */
for(;;) {
@@ -2064,6 +2101,8 @@ static int link_path_walk(const char *name, struct nameidata *nd)
nd->last.hash_len = hash_len;
nd->last.name = name;
nd->last_type = type;
/* be ready for the next security_inode_permission() */
refresh_lookup(nd);

name += hashlen_len(hash_len);
if (!*name)
@@ -428,6 +428,10 @@
* security module does not know about attribute or a negative error code
* to abort the copy up. Note that the caller is responsible for reading
* and writing the xattrs as this hook is merely a filter.
* @nameidata_put_lookup:
* Deallocate and clear the current's nameidata->lookup.security field.
* @lookup->security contains the security structure to be freed.
* @inode is the last associated inode to the path walk
*
* Security hooks for file operations
*
@@ -1514,6 +1518,8 @@ union security_list_options {
void (*inode_getsecid)(struct inode *inode, u32 *secid);
int (*inode_copy_up)(struct dentry *src, struct cred **new);
int (*inode_copy_up_xattr)(const char *name);
void (*nameidata_put_lookup)(struct nameidata_lookup *lookup,
struct inode *inode);

int (*file_permission)(struct file *file, int mask);
int (*file_alloc_security)(struct file *file);
@@ -1805,6 +1811,7 @@ struct security_hook_heads {
struct list_head inode_getsecid;
struct list_head inode_copy_up;
struct list_head inode_copy_up_xattr;
struct list_head nameidata_put_lookup;
struct list_head file_permission;
struct list_head file_alloc_security;
struct list_head file_free_security;
@@ -14,7 +14,19 @@ enum { MAX_NESTED_LINKS = 8 };
/*
* Type of the last component on LOOKUP_PARENT
*/
enum {LAST_NORM, LAST_ROOT, LAST_DOT, LAST_DOTDOT, LAST_BIND};
enum namei_type {LAST_NORM, LAST_ROOT, LAST_DOT, LAST_DOTDOT, LAST_BIND};

#ifdef CONFIG_SECURITY
struct nameidata_lookup {
void *security;
enum namei_type type;
};

struct inode;

extern struct nameidata_lookup *current_nameidata_lookup(
const struct inode *inode);
#endif

/*
* The bitmask for a lookup event:
@@ -31,6 +31,7 @@
#include <linux/string.h>
#include <linux/mm.h>
#include <linux/fs.h>
#include <linux/namei.h>

struct linux_binprm;
struct cred;
@@ -302,6 +303,8 @@ int security_inode_listsecurity(struct inode *inode, char *buffer, size_t buffer
void security_inode_getsecid(struct inode *inode, u32 *secid);
int security_inode_copy_up(struct dentry *src, struct cred **new);
int security_inode_copy_up_xattr(const char *name);
void security_nameidata_put_lookup(struct nameidata_lookup *lookup,
struct inode *inode);
int security_file_permission(struct file *file, int mask);
int security_file_alloc(struct file *file);
void security_file_free(struct file *file);
@@ -808,6 +811,10 @@ static inline int security_inode_copy_up_xattr(const char *name)
return -EOPNOTSUPP;
}

static inline void security_nameidata_put_lookup(
struct nameidata_lookup *lookup, struct inode *inode)
{ }

static inline int security_file_permission(struct file *file, int mask)
{
return 0;
@@ -857,6 +857,13 @@ int security_inode_copy_up_xattr(const char *name)
}
EXPORT_SYMBOL(security_inode_copy_up_xattr);

void security_nameidata_put_lookup(struct nameidata_lookup *lookup,
struct inode *inode)
{
call_void_hook(nameidata_put_lookup, lookup, inode);
}
EXPORT_SYMBOL(security_nameidata_put_lookup);

int security_file_permission(struct file *file, int mask)
{
int ret;

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