Add a new LSM hook named inode_touch_atime which is needed to deny
indirect update of extended file attributes (i.e. access time) which are
not catched by the inode_setattr hook. By creating a new hook instead of
calling inode_setattr, we avoid to simulate a useless struct iattr.
This hook allows to create read-only environments as with read-only
mount points. It can also take care of anonymous inodes.
Signed-off-by: Mickaël Salaün <mic@xxxxxxxxxxx>
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Cc: Casey Schaufler <casey@xxxxxxxxxxxxxxxx>
Cc: Dmitry Kasatkin <dmitry.kasatkin@xxxxxxxxx>
Cc: Eric Paris <eparis@xxxxxxxxxxxxxx>
Cc: James Morris <james.l.morris@xxxxxxxxxx>
Cc: John Johansen <john.johansen@xxxxxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Kentaro Takeda <takedakn@xxxxxxxxxxxxx>
Cc: Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx>
Cc: Paul Moore <paul@xxxxxxxxxxxxxx>
Cc: Serge E. Hallyn <serge@xxxxxxxxxx>
Cc: Stephen Smalley <sds@xxxxxxxxxxxxx>
Cc: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
---
fs/inode.c | 5 ++++-
include/linux/lsm_hooks.h | 8 ++++++++
include/linux/security.h | 8 ++++++++
security/security.c | 9 +++++++++
4 files changed, 29 insertions(+), 1 deletion(-)
diff --git a/fs/inode.c b/fs/inode.c
index 88110fd0b282..8e7519196942 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -1706,6 +1706,10 @@ void touch_atime(const struct path *path)
if (!__atime_needs_update(path, inode, false))
return;
+ now = current_time(inode);
+ if (security_inode_touch_atime(path, &now))
+ return;
+
if (!sb_start_write_trylock(inode->i_sb))
return;
@@ -1720,7 +1724,6 @@ void touch_atime(const struct path *path)
* We may also fail on filesystems that have the ability to make parts
* of the fs read only, e.g. subvolumes in Btrfs.
*/
- now = current_time(inode);
update_time(inode, &now, S_ATIME);
__mnt_drop_write(mnt);
skip_update:
diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 558adfa5c8a8..e77051715e6b 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -428,6 +428,11 @@
* 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.
+ * @inode_touch_atime:
+ * Check permission before updating access time.
+ * @path contains the path structure for the file.
+ * @ts contains the current time.
+ * Return 0 if permission is granted.
*
* Security hooks for file operations
*
@@ -1458,6 +1463,8 @@ 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);
+ int (*inode_touch_atime)(const struct path *path,
+ const struct timespec *ts);
int (*file_permission)(struct file *file, int mask);
int (*file_alloc_security)(struct file *file);
@@ -1731,6 +1738,7 @@ 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 inode_touch_atime;
struct list_head file_permission;
struct list_head file_alloc_security;
struct list_head file_free_security;
diff --git a/include/linux/security.h b/include/linux/security.h
index c2125e9093e8..619f44c290a5 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -30,6 +30,7 @@
#include <linux/string.h>
#include <linux/mm.h>
#include <linux/fs.h>
+#include <linux/time.h>
struct linux_binprm;
struct cred;
@@ -288,6 +289,7 @@ 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);
+int security_inode_touch_atime(const struct path *path, const struct timespec *ts);
int security_file_permission(struct file *file, int mask);
int security_file_alloc(struct file *file);
void security_file_free(struct file *file);
@@ -781,6 +783,12 @@ static inline int security_inode_copy_up_xattr(const char *name)
return -EOPNOTSUPP;
}
+static inline int security_inode_touch_atime(const struct path *path, const
+ struct timespec *ts)
+{
+ return 0;
+}
+
static inline int security_file_permission(struct file *file, int mask)
{
return 0;
diff --git a/security/security.c b/security/security.c
index f825304f04a7..cd093c4b4115 100644
--- a/security/security.c
+++ b/security/security.c
@@ -769,6 +769,13 @@ int security_inode_copy_up_xattr(const char *name)
}
EXPORT_SYMBOL(security_inode_copy_up_xattr);
+int security_inode_touch_atime(const struct path *path,
+ const struct timespec *ts)
+{
+ return call_int_hook(inode_touch_atime, 0, path, ts);
+}
+EXPORT_SYMBOL(security_inode_touch_atime);
+
int security_file_permission(struct file *file, int mask)
{
int ret;
@@ -1711,6 +1718,8 @@ struct security_hook_heads security_hook_heads = {
LIST_HEAD_INIT(security_hook_heads.inode_copy_up),
.inode_copy_up_xattr =
LIST_HEAD_INIT(security_hook_heads.inode_copy_up_xattr),
+ .inode_touch_atime =
+ LIST_HEAD_INIT(security_hook_heads.inode_touch_atime),
.file_permission =
LIST_HEAD_INIT(security_hook_heads.file_permission),
.file_alloc_security =
--
2.11.0
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