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Subject[PATCH bpf-next v8 01/11] fs,security: Add a security blob to nameidata
Date
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
---
fs/namei.c | 39 +++++++++++++++++++++++++++++++++++++++
include/linux/lsm_hooks.h | 7 +++++++
include/linux/namei.h | 14 +++++++++++++-
include/linux/security.h | 7 +++++++
security/security.c | 7 +++++++
5 files changed, 73 insertions(+), 1 deletion(-)

diff --git a/fs/namei.c b/fs/namei.c
index 921ae32dbc80..d592b3fb0d1e 100644
--- a/fs/namei.c
+++ b/fs/namei.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)
@@ -515,6 +518,9 @@ 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;
}

@@ -522,6 +528,7 @@ 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)
diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 7161d8e7ee79..d71cf183f0be 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -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;
diff --git a/include/linux/namei.h b/include/linux/namei.h
index a982bb7cd480..ba08cbb41f97 100644
--- a/include/linux/namei.h
+++ b/include/linux/namei.h
@@ -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:
diff --git a/include/linux/security.h b/include/linux/security.h
index 73f1ef625d40..b1fd4370daf8 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -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;
diff --git a/security/security.c b/security/security.c
index 1cd8526cb0b7..17053c7a1a77 100644
--- a/security/security.c
+++ b/security/security.c
@@ -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;
--
2.16.2
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