Thanks for the doc.
On 01/10/2022 17:49, Günther Noack wrote:
Like path_truncate, the file_truncate hook also restricts file
truncation, but is called in the cases where truncation is attempted
on an already-opened file.
This is required in a subsequent commit to handle ftruncate()
operations differently to truncate() operations.
Acked-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Acked-by: John Johansen <john.johansen@xxxxxxxxxxxxx>
Signed-off-by: Günther Noack <gnoack3000@xxxxxxxxx>
---
fs/namei.c | 2 +-
fs/open.c | 2 +-
include/linux/lsm_hook_defs.h | 1 +
include/linux/lsm_hooks.h | 10 +++++++++-
include/linux/security.h | 6 ++++++
security/apparmor/lsm.c | 6 ++++++
security/security.c | 5 +++++
security/tomoyo/tomoyo.c | 13 +++++++++++++
8 files changed, 42 insertions(+), 3 deletions(-)
diff --git a/fs/namei.c b/fs/namei.c
index 53b4bc094db2..0e419bd30f8e 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -3211,7 +3211,7 @@ static int handle_truncate(struct user_namespace *mnt_userns, struct file *filp)
if (error)
return error;
- error = security_path_truncate(path);
+ error = security_file_truncate(filp);
if (!error) {
error = do_truncate(mnt_userns, path->dentry, 0,
ATTR_MTIME|ATTR_CTIME|ATTR_OPEN,
diff --git a/fs/open.c b/fs/open.c
index cf7e5c350a54..0fa861873245 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -188,7 +188,7 @@ long do_sys_ftruncate(unsigned int fd, loff_t length, int small)
if (IS_APPEND(file_inode(f.file)))
goto out_putf;
sb_start_write(inode->i_sb);
- error = security_path_truncate(&f.file->f_path);
+ error = security_file_truncate(f.file);
if (!error)
error = do_truncate(file_mnt_user_ns(f.file), dentry, length,
ATTR_MTIME | ATTR_CTIME, f.file);
diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
index 60fff133c0b1..dee35ab253ba 100644
--- a/include/linux/lsm_hook_defs.h
+++ b/include/linux/lsm_hook_defs.h
@@ -177,6 +177,7 @@ LSM_HOOK(int, 0, file_send_sigiotask, struct task_struct *tsk,
struct fown_struct *fown, int sig)
LSM_HOOK(int, 0, file_receive, struct file *file)
LSM_HOOK(int, 0, file_open, struct file *file)
+LSM_HOOK(int, 0, file_truncate, struct file *file)
LSM_HOOK(int, 0, task_alloc, struct task_struct *task,
unsigned long clone_flags)
LSM_HOOK(void, LSM_RET_VOID, task_free, struct task_struct *task)
diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 3aa6030302f5..4acc975f28d9 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -409,7 +409,9 @@
* @attr is the iattr structure containing the new file attributes.
* Return 0 if permission is granted.
* @path_truncate:
- * Check permission before truncating a file.
+ * Check permission before truncating the file indicated by path.
+ * Note that truncation permissions may also be checked based on
+ * already opened files, using the @file_truncate hook.
The documentation comments (mostly) use tabs, not spaces.
* @path contains the path structure for the file.
* Return 0 if permission is granted.
* @inode_getattr:
@@ -598,6 +600,12 @@
* to receive an open file descriptor via socket IPC.
* @file contains the file structure being received.
* Return 0 if permission is granted.
+ * @file_truncate:
+ * Check permission before truncating a file, i.e. using ftruncate.
+ * Note that truncation permission may also be checked based on the path,
+ * using the @path_truncate hook.
Same here.
+ * @file contains the file structure for the file.
+ * Return 0 if permission is granted.
* @file_open:
* Save open-time permission checking state for later use upon
* file_permission, and recheck access if anything has changed
diff --git a/include/linux/security.h b/include/linux/security.h
index 7bd0c490703d..f80b23382dd9 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -394,6 +394,7 @@ int security_file_send_sigiotask(struct task_struct *tsk,
struct fown_struct *fown, int sig);
int security_file_receive(struct file *file);
int security_file_open(struct file *file);
+int security_file_truncate(struct file *file);
int security_task_alloc(struct task_struct *task, unsigned long clone_flags);
void security_task_free(struct task_struct *task);
int security_cred_alloc_blank(struct cred *cred, gfp_t gfp);
@@ -1011,6 +1012,11 @@ static inline int security_file_open(struct file *file)
return 0;
}
+static inline int security_file_truncate(struct file *file)
+{
+ return 0;
+}
+
static inline int security_task_alloc(struct task_struct *task,
unsigned long clone_flags)
{
diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c
index e29cade7b662..98ecb7f221b8 100644
--- a/security/apparmor/lsm.c
+++ b/security/apparmor/lsm.c
@@ -329,6 +329,11 @@ static int apparmor_path_truncate(const struct path *path)
return common_perm_cond(OP_TRUNC, path, MAY_WRITE | AA_MAY_SETATTR);
}
+static int apparmor_file_truncate(struct file *file)
+{
+ return apparmor_path_truncate(&file->f_path);
+}
+
static int apparmor_path_symlink(const struct path *dir, struct dentry *dentry,
const char *old_name)
{
@@ -1232,6 +1237,7 @@ static struct security_hook_list apparmor_hooks[] __lsm_ro_after_init = {
LSM_HOOK_INIT(mmap_file, apparmor_mmap_file),
LSM_HOOK_INIT(file_mprotect, apparmor_file_mprotect),
LSM_HOOK_INIT(file_lock, apparmor_file_lock),
+ LSM_HOOK_INIT(file_truncate, apparmor_file_truncate),
LSM_HOOK_INIT(getprocattr, apparmor_getprocattr),
LSM_HOOK_INIT(setprocattr, apparmor_setprocattr),
diff --git a/security/security.c b/security/security.c
index 4b95de24bc8d..d73e423005c3 100644
--- a/security/security.c
+++ b/security/security.c
@@ -1650,6 +1650,11 @@ int security_file_open(struct file *file)
return fsnotify_perm(file, MAY_OPEN);
}
+int security_file_truncate(struct file *file)
+{
+ return call_int_hook(file_truncate, 0, file);
+}
+
int security_task_alloc(struct task_struct *task, unsigned long clone_flags)
{
int rc = lsm_task_alloc(task);
diff --git a/security/tomoyo/tomoyo.c b/security/tomoyo/tomoyo.c
index 71e82d855ebf..af04a7b7eb28 100644
--- a/security/tomoyo/tomoyo.c
+++ b/security/tomoyo/tomoyo.c
@@ -134,6 +134,18 @@ static int tomoyo_path_truncate(const struct path *path)
return tomoyo_path_perm(TOMOYO_TYPE_TRUNCATE, path, NULL);
}
+/**
+ * tomoyo_file_truncate - Target for security_file_truncate().
+ *
+ * @file: Pointer to "struct file".
+ *
+ * Returns 0 on success, negative value otherwise.
+ */
+static int tomoyo_file_truncate(struct file *file)
+{
+ return tomoyo_path_truncate(&file->f_path);
+}
+
/**
* tomoyo_path_unlink - Target for security_path_unlink().
*
@@ -545,6 +557,7 @@ static struct security_hook_list tomoyo_hooks[] __lsm_ro_after_init = {
LSM_HOOK_INIT(bprm_check_security, tomoyo_bprm_check_security),
LSM_HOOK_INIT(file_fcntl, tomoyo_file_fcntl),
LSM_HOOK_INIT(file_open, tomoyo_file_open),
+ LSM_HOOK_INIT(file_truncate, tomoyo_file_truncate),
LSM_HOOK_INIT(path_truncate, tomoyo_path_truncate),
LSM_HOOK_INIT(path_unlink, tomoyo_path_unlink),
LSM_HOOK_INIT(path_mkdir, tomoyo_path_mkdir),
