ima: handle idmapped mounts

IMA does sometimes access the inode's i_uid and compares it against the
rules' fowner. Enable IMA to handle idmapped mounts by passing down the
mount's user namespace. We simply make use of the helpers we introduced
before. If the initial user namespace is passed nothing changes so
non-idmapped mounts will see identical behavior as before.

Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Christian Brauner <[e-mail]>

fs/attr.c

···
 
 	if (!error) {
 		fsnotify_change(dentry, ia_valid);
-		ima_inode_post_setattr(dentry);
+		ima_inode_post_setattr(mnt_userns, dentry);
 		evm_inode_post_setattr(dentry, ia_valid);
 	}
 

fs/namei.c

···
 		inode->i_state |= I_LINKABLE;
 		spin_unlock(&inode->i_lock);
 	}
-	ima_post_create_tmpfile(inode);
+	ima_post_create_tmpfile(mnt_userns, inode);
 	return child;
 
 out_err:
···
 			error = vfs_create(mnt_userns, path.dentry->d_inode,
 					   dentry, mode, true);
 			if (!error)
-				ima_post_path_mknod(dentry);
+				ima_post_path_mknod(mnt_userns, dentry);
 			break;
 		case S_IFCHR: case S_IFBLK:
 			error = vfs_mknod(mnt_userns, path.dentry->d_inode,

include/linux/ima.h

···
 #ifdef CONFIG_IMA
 extern int ima_bprm_check(struct linux_binprm *bprm);
 extern int ima_file_check(struct file *file, int mask);
-extern void ima_post_create_tmpfile(struct inode *inode);
+extern void ima_post_create_tmpfile(struct user_namespace *mnt_userns,
+				    struct inode *inode);
 extern void ima_file_free(struct file *file);
 extern int ima_file_mmap(struct file *file, unsigned long prot);
 extern int ima_file_mprotect(struct vm_area_struct *vma, unsigned long prot);
···
 			 bool contents);
 extern int ima_post_read_file(struct file *file, void *buf, loff_t size,
 			      enum kernel_read_file_id id);
-extern void ima_post_path_mknod(struct dentry *dentry);
+extern void ima_post_path_mknod(struct user_namespace *mnt_userns,
+				struct dentry *dentry);
 extern int ima_file_hash(struct file *file, char *buf, size_t buf_size);
 extern int ima_inode_hash(struct inode *inode, char *buf, size_t buf_size);
 extern void ima_kexec_cmdline(int kernel_fd, const void *buf, int size);
···
 	return 0;
 }
 
-static inline void ima_post_create_tmpfile(struct inode *inode)
+static inline void ima_post_create_tmpfile(struct user_namespace *mnt_userns,
+					   struct inode *inode)
 {
 }
 
···
 	return 0;
 }
 
-static inline void ima_post_path_mknod(struct dentry *dentry)
+static inline void ima_post_path_mknod(struct user_namespace *mnt_userns,
+				       struct dentry *dentry)
 {
 	return;
 }
···
 
 #ifdef CONFIG_IMA_APPRAISE
 extern bool is_ima_appraise_enabled(void);
-extern void ima_inode_post_setattr(struct dentry *dentry);
+extern void ima_inode_post_setattr(struct user_namespace *mnt_userns,
+				   struct dentry *dentry);
 extern int ima_inode_setxattr(struct dentry *dentry, const char *xattr_name,
 		       const void *xattr_value, size_t xattr_value_len);
 extern int ima_inode_removexattr(struct dentry *dentry, const char *xattr_name);
···
 	return 0;
 }
 
-static inline void ima_inode_post_setattr(struct dentry *dentry)
+static inline void ima_inode_post_setattr(struct user_namespace *mnt_userns,
+					  struct dentry *dentry)
 {
 	return;
 }

security/integrity/ima/ima.h

···
 #endif /* CONFIG_IMA_QUEUE_EARLY_BOOT_KEYS */
 
 /* LIM API function definitions */
-int ima_get_action(struct inode *inode, const struct cred *cred, u32 secid,
-		   int mask, enum ima_hooks func, int *pcr,
+int ima_get_action(struct user_namespace *mnt_userns, struct inode *inode,
+		   const struct cred *cred, u32 secid, int mask,
+		   enum ima_hooks func, int *pcr,
 		   struct ima_template_desc **template_desc,
 		   const char *keyring);
 int ima_must_measure(struct inode *inode, int mask, enum ima_hooks func);
···
 			   struct evm_ima_xattr_data *xattr_value,
 			   int xattr_len, const struct modsig *modsig, int pcr,
 			   struct ima_template_desc *template_desc);
-void process_buffer_measurement(struct inode *inode, const void *buf, int size,
+void process_buffer_measurement(struct user_namespace *mnt_userns,
+				struct inode *inode, const void *buf, int size,
 				const char *eventname, enum ima_hooks func,
 				int pcr, const char *keyring);
 void ima_audit_measurement(struct integrity_iint_cache *iint,
···
 const char *ima_d_path(const struct path *path, char **pathbuf, char *filename);
 
 /* IMA policy related functions */
-int ima_match_policy(struct inode *inode, const struct cred *cred, u32 secid,
-		     enum ima_hooks func, int mask, int flags, int *pcr,
+int ima_match_policy(struct user_namespace *mnt_userns, struct inode *inode,
+		     const struct cred *cred, u32 secid, enum ima_hooks func,
+		     int mask, int flags, int *pcr,
 		     struct ima_template_desc **template_desc,
 		     const char *keyring);
 void ima_init_policy(void);
···
 			     struct file *file, const unsigned char *filename,
 			     struct evm_ima_xattr_data *xattr_value,
 			     int xattr_len, const struct modsig *modsig);
-int ima_must_appraise(struct inode *inode, int mask, enum ima_hooks func);
+int ima_must_appraise(struct user_namespace *mnt_userns, struct inode *inode,
+		      int mask, enum ima_hooks func);
 void ima_update_xattr(struct integrity_iint_cache *iint, struct file *file);
 enum integrity_status ima_get_cache_status(struct integrity_iint_cache *iint,
 					   enum ima_hooks func);
···
 	return INTEGRITY_UNKNOWN;
 }
 
-static inline int ima_must_appraise(struct inode *inode, int mask,
+static inline int ima_must_appraise(struct user_namespace *mnt_userns,
+				    struct inode *inode, int mask,
 				    enum ima_hooks func)
 {
 	return 0;

security/integrity/ima/ima_api.c

···
 
 /**
  * ima_get_action - appraise & measure decision based on policy.
+ * @mnt_userns:	user namespace of the mount the inode was found from
  * @inode: pointer to the inode associated with the object being validated
  * @cred: pointer to credentials structure to validate
  * @secid: secid of the task being validated
···
  * Returns IMA_MEASURE, IMA_APPRAISE mask.
  *
  */
-int ima_get_action(struct inode *inode, const struct cred *cred, u32 secid,
-		   int mask, enum ima_hooks func, int *pcr,
+int ima_get_action(struct user_namespace *mnt_userns, struct inode *inode,
+		   const struct cred *cred, u32 secid, int mask,
+		   enum ima_hooks func, int *pcr,
 		   struct ima_template_desc **template_desc,
 		   const char *keyring)
 {
···
 
 	flags &= ima_policy_flag;
 
-	return ima_match_policy(inode, cred, secid, func, mask, flags, pcr,
-				template_desc, keyring);
+	return ima_match_policy(mnt_userns, inode, cred, secid, func, mask,
+				flags, pcr, template_desc, keyring);
 }
 
 /*

security/integrity/ima/ima_appraise.c

···
  *
  * Return 1 to appraise or hash
  */
-int ima_must_appraise(struct inode *inode, int mask, enum ima_hooks func)
+int ima_must_appraise(struct user_namespace *mnt_userns, struct inode *inode,
+		      int mask, enum ima_hooks func)
 {
 	u32 secid;
 
···
 		return 0;
 
 	security_task_getsecid(current, &secid);
-	return ima_match_policy(inode, current_cred(), secid, func, mask,
-				IMA_APPRAISE | IMA_HASH, NULL, NULL, NULL);
+	return ima_match_policy(mnt_userns, inode, current_cred(), secid, func,
+				mask, IMA_APPRAISE | IMA_HASH, NULL, NULL, NULL);
 }
 
 static int ima_fix_xattr(struct dentry *dentry,
···
 
 		rc = is_binary_blacklisted(digest, digestsize);
 		if ((rc == -EPERM) && (iint->flags & IMA_MEASURE))
-			process_buffer_measurement(NULL, digest, digestsize,
+			process_buffer_measurement(&init_user_ns, NULL, digest, digestsize,
 						   "blacklisted-hash", NONE,
 						   pcr, NULL);
 	}
···
 
 /**
  * ima_inode_post_setattr - reflect file metadata changes
+ * @mnt_userns:	user namespace of the mount the inode was found from
  * @dentry: pointer to the affected dentry
  *
  * Changes to a dentry's metadata might result in needing to appraise.
···
  * This function is called from notify_change(), which expects the caller
  * to lock the inode's i_mutex.
  */
-void ima_inode_post_setattr(struct dentry *dentry)
+void ima_inode_post_setattr(struct user_namespace *mnt_userns,
+			    struct dentry *dentry)
 {
 	struct inode *inode = d_backing_inode(dentry);
 	struct integrity_iint_cache *iint;
···
 	    || !(inode->i_opflags & IOP_XATTR))
 		return;
 
-	action = ima_must_appraise(inode, MAY_ACCESS, POST_SETATTR);
+	action = ima_must_appraise(mnt_userns, inode, MAY_ACCESS, POST_SETATTR);
 	if (!action)
 		__vfs_removexattr(&init_user_ns, dentry, XATTR_NAME_IMA);
 	iint = integrity_iint_find(inode);

security/integrity/ima/ima_asymmetric_keys.c

···
  */
 
 #include <keys/asymmetric-type.h>
+#include <linux/user_namespace.h>
 #include "ima.h"
 
 /**
···
 	 * if the IMA policy is configured to measure a key linked
 	 * to the given keyring.
 	 */
-	process_buffer_measurement(NULL, payload, payload_len,
+	process_buffer_measurement(&init_user_ns, NULL, payload, payload_len,
 				   keyring->description, KEY_CHECK, 0,
 				   keyring->description);
 }

security/integrity/ima/ima_main.c

···
 	 * bitmask based on the appraise/audit/measurement policy.
 	 * Included is the appraise submask.
 	 */
-	action = ima_get_action(inode, cred, secid, mask, func, &pcr,
-				&template_desc, NULL);
+	action = ima_get_action(file_mnt_user_ns(file), inode, cred, secid,
+				mask, func, &pcr, &template_desc, NULL);
 	violation_check = ((func == FILE_CHECK || func == MMAP_CHECK) &&
 			   (ima_policy_flag & IMA_MEASURE));
 	if (!action && !violation_check)
···
 
 	security_task_getsecid(current, &secid);
 	inode = file_inode(vma->vm_file);
-	action = ima_get_action(inode, current_cred(), secid, MAY_EXEC,
-				MMAP_CHECK, &pcr, &template, 0);
+	action = ima_get_action(file_mnt_user_ns(vma->vm_file), inode,
+				current_cred(), secid, MAY_EXEC, MMAP_CHECK,
+				&pcr, &template, 0);
 
 	/* Is the mmap'ed file in policy? */
 	if (!(action & (IMA_MEASURE | IMA_APPRAISE_SUBMASK)))
···
 
 /**
  * ima_post_create_tmpfile - mark newly created tmpfile as new
+ * @mnt_userns:	user namespace of the mount the inode was found from
  * @file : newly created tmpfile
  *
  * No measuring, appraising or auditing of newly created tmpfiles is needed.
  * Skip calling process_measurement(), but indicate which newly, created
  * tmpfiles are in policy.
  */
-void ima_post_create_tmpfile(struct inode *inode)
+void ima_post_create_tmpfile(struct user_namespace *mnt_userns,
+			     struct inode *inode)
 {
 	struct integrity_iint_cache *iint;
 	int must_appraise;
 
-	must_appraise = ima_must_appraise(inode, MAY_ACCESS, FILE_CHECK);
+	must_appraise = ima_must_appraise(mnt_userns, inode, MAY_ACCESS,
+					  FILE_CHECK);
 	if (!must_appraise)
 		return;
 
···
 
 /**
  * ima_post_path_mknod - mark as a new inode
+ * @mnt_userns:	user namespace of the mount the inode was found from
  * @dentry: newly created dentry
  *
  * Mark files created via the mknodat syscall as new, so that the
  * file data can be written later.
  */
-void ima_post_path_mknod(struct dentry *dentry)
+void ima_post_path_mknod(struct user_namespace *mnt_userns,
+			 struct dentry *dentry)
 {
 	struct integrity_iint_cache *iint;
 	struct inode *inode = dentry->d_inode;
 	int must_appraise;
 
-	must_appraise = ima_must_appraise(inode, MAY_ACCESS, FILE_CHECK);
+	must_appraise = ima_must_appraise(mnt_userns, inode, MAY_ACCESS,
+					  FILE_CHECK);
 	if (!must_appraise)
 		return;
 
···
 
 /*
  * process_buffer_measurement - Measure the buffer to ima log.
+ * @mnt_userns:	user namespace of the mount the inode was found from
  * @inode: inode associated with the object being measured (NULL for KEY_CHECK)
  * @buf: pointer to the buffer that needs to be added to the log.
  * @size: size of buffer(in bytes).
···
  *
  * Based on policy, the buffer is measured into the ima log.
  */
-void process_buffer_measurement(struct inode *inode, const void *buf, int size,
+void process_buffer_measurement(struct user_namespace *mnt_userns,
+				struct inode *inode, const void *buf, int size,
 				const char *eventname, enum ima_hooks func,
 				int pcr, const char *keyring)
 {
···
 	 */
 	if (func) {
 		security_task_getsecid(current, &secid);
-		action = ima_get_action(inode, current_cred(), secid, 0, func,
-					&pcr, &template, keyring);
+		action = ima_get_action(mnt_userns, inode, current_cred(),
+					secid, 0, func, &pcr, &template,
+					keyring);
 		if (!(action & IMA_MEASURE))
 			return;
 	}
···
 	if (!f.file)
 		return;
 
-	process_buffer_measurement(file_inode(f.file), buf, size,
-				   "kexec-cmdline", KEXEC_CMDLINE, 0, NULL);
+	process_buffer_measurement(file_mnt_user_ns(f.file), file_inode(f.file),
+				   buf, size, "kexec-cmdline", KEXEC_CMDLINE, 0,
+				   NULL);
 	fdput(f);
 }
 

security/integrity/ima/ima_policy.c

···
 /**
  * ima_match_rules - determine whether an inode matches the policy rule.
  * @rule: a pointer to a rule
+ * @mnt_userns:	user namespace of the mount the inode was found from
  * @inode: a pointer to an inode
  * @cred: a pointer to a credentials structure for user validation
  * @secid: the secid of the task to be validated
···
  *
  * Returns true on rule match, false on failure.
  */
-static bool ima_match_rules(struct ima_rule_entry *rule, struct inode *inode,
-			    const struct cred *cred, u32 secid,
-			    enum ima_hooks func, int mask,
+static bool ima_match_rules(struct ima_rule_entry *rule,
+			    struct user_namespace *mnt_userns,
+			    struct inode *inode, const struct cred *cred,
+			    u32 secid, enum ima_hooks func, int mask,
 			    const char *keyring)
 {
 	int i;
···
 	}
 
 	if ((rule->flags & IMA_FOWNER) &&
-	    !rule->fowner_op(inode->i_uid, rule->fowner))
+	    !rule->fowner_op(i_uid_into_mnt(mnt_userns, inode), rule->fowner))
 		return false;
 	for (i = 0; i < MAX_LSM_RULES; i++) {
 		int rc = 0;
···
 
 /**
  * ima_match_policy - decision based on LSM and other conditions
+ * @mnt_userns:	user namespace of the mount the inode was found from
  * @inode: pointer to an inode for which the policy decision is being made
  * @cred: pointer to a credentials structure for which the policy decision is
  *        being made
···
  * list when walking it.  Reads are many orders of magnitude more numerous
  * than writes so ima_match_policy() is classical RCU candidate.
  */
-int ima_match_policy(struct inode *inode, const struct cred *cred, u32 secid,
-		     enum ima_hooks func, int mask, int flags, int *pcr,
+int ima_match_policy(struct user_namespace *mnt_userns, struct inode *inode,
+		     const struct cred *cred, u32 secid, enum ima_hooks func,
+		     int mask, int flags, int *pcr,
 		     struct ima_template_desc **template_desc,
 		     const char *keyring)
 {
···
 		if (!(entry->action & actmask))
 			continue;
 
-		if (!ima_match_rules(entry, inode, cred, secid, func, mask,
-				     keyring))
+		if (!ima_match_rules(entry, mnt_userns, inode, cred, secid,
+				     func, mask, keyring))
 			continue;
 
 		action |= entry->flags & IMA_ACTION_FLAGS;

security/integrity/ima/ima_queue_keys.c

···
  *       Enables deferred processing of keys
  */
 
+#include <linux/user_namespace.h>
 #include <linux/workqueue.h>
 #include <keys/asymmetric-type.h>
 #include "ima.h"
···
 
 	list_for_each_entry_safe(entry, tmp, &ima_keys, list) {
 		if (!timer_expired)
-			process_buffer_measurement(NULL, entry->payload,
+			process_buffer_measurement(&init_user_ns, NULL,
+						   entry->payload,
 						   entry->payload_len,
 						   entry->keyring_name,
 						   KEY_CHECK, 0,