apparmor: handle idmapped mounts

The i_uid and i_gid are mostly used when logging for AppArmor. This is
broken in a bunch of places where the global root id is reported instead
of the i_uid or i_gid of the file. Nonetheless, be kind and log the
mapped inode if we're coming from an idmapped mount. 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/20210121131959.646623-26-christian.brauner@ubuntu.com
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

security/apparmor/domain.c

@@ -10,12 +10,14 @@
 
 #include <linux/errno.h>
 #include <linux/fdtable.h>
+#include <linux/fs.h>
 #include <linux/file.h>
 #include <linux/mount.h>
 #include <linux/syscalls.h>
 #include <linux/tracehook.h>
 #include <linux/personality.h>
 #include <linux/xattr.h>
+#include <linux/user_namespace.h>
 
 #include "include/audit.h"
 #include "include/apparmorfs.h"
@@ -858,8 +860,10 @@ int apparmor_bprm_creds_for_exec(struct linux_binprm *bprm)
 	const char *info = NULL;
 	int error = 0;
 	bool unsafe = false;
+	kuid_t i_uid = i_uid_into_mnt(file_mnt_user_ns(bprm->file),
+				      file_inode(bprm->file));
 	struct path_cond cond = {
-		file_inode(bprm->file)->i_uid,
+		i_uid,
 		file_inode(bprm->file)->i_mode
 	};
 
@@ -967,8 +971,7 @@ int apparmor_bprm_creds_for_exec(struct linux_binprm *bprm)
 	error = fn_for_each(label, profile,
 			aa_audit_file(profile, &nullperms, OP_EXEC, MAY_EXEC,
 				      bprm->filename, NULL, new,
-				      file_inode(bprm->file)->i_uid, info,
-				      error));
+				      i_uid, info, error));
 	aa_put_label(new);
 	goto done;
 }

security/apparmor/file.c

@@ -11,6 +11,8 @@
 #include <linux/tty.h>
 #include <linux/fdtable.h>
 #include <linux/file.h>
+#include <linux/fs.h>
+#include <linux/mount.h>
 
 #include "include/apparmor.h"
 #include "include/audit.h"
@@ -509,7 +511,7 @@ static int __file_path_perm(const char *op, struct aa_label *label,
 	struct aa_profile *profile;
 	struct aa_perms perms = {};
 	struct path_cond cond = {
-		.uid = file_inode(file)->i_uid,
+		.uid = i_uid_into_mnt(file_mnt_user_ns(file), file_inode(file)),
 		.mode = file_inode(file)->i_mode
 	};
 	char *buffer;

security/apparmor/lsm.c

@@ -224,8 +224,10 @@ static int common_perm(const char *op, const struct path *path, u32 mask,
  */
 static int common_perm_cond(const char *op, const struct path *path, u32 mask)
 {
-	struct path_cond cond = { d_backing_inode(path->dentry)->i_uid,
-				  d_backing_inode(path->dentry)->i_mode
+	struct user_namespace *mnt_userns = mnt_user_ns(path->mnt);
+	struct path_cond cond = {
+		i_uid_into_mnt(mnt_userns, d_backing_inode(path->dentry)),
+		d_backing_inode(path->dentry)->i_mode
 	};
 
 	if (!path_mediated_fs(path->dentry))
@@ -266,12 +268,13 @@ static int common_perm_rm(const char *op, const struct path *dir,
 			  struct dentry *dentry, u32 mask)
 {
 	struct inode *inode = d_backing_inode(dentry);
+	struct user_namespace *mnt_userns = mnt_user_ns(dir->mnt);
 	struct path_cond cond = { };
 
 	if (!inode || !path_mediated_fs(dentry))
 		return 0;
 
-	cond.uid = inode->i_uid;
+	cond.uid = i_uid_into_mnt(mnt_userns, inode);
 	cond.mode = inode->i_mode;
 
 	return common_perm_dir_dentry(op, dir, dentry, mask, &cond);
@@ -361,12 +364,14 @@ static int apparmor_path_rename(const struct path *old_dir, struct dentry *old_d
 
 	label = begin_current_label_crit_section();
 	if (!unconfined(label)) {
+		struct user_namespace *mnt_userns = mnt_user_ns(old_dir->mnt);
 		struct path old_path = { .mnt = old_dir->mnt,
 					 .dentry = old_dentry };
 		struct path new_path = { .mnt = new_dir->mnt,
 					 .dentry = new_dentry };
-		struct path_cond cond = { d_backing_inode(old_dentry)->i_uid,
-					  d_backing_inode(old_dentry)->i_mode
+		struct path_cond cond = {
+			i_uid_into_mnt(mnt_userns, d_backing_inode(old_dentry)),
+			d_backing_inode(old_dentry)->i_mode
 		};
 
 		error = aa_path_perm(OP_RENAME_SRC, label, &old_path, 0,
@@ -420,8 +425,12 @@ static int apparmor_file_open(struct file *file)
 
 	label = aa_get_newest_cred_label(file->f_cred);
 	if (!unconfined(label)) {
+		struct user_namespace *mnt_userns = file_mnt_user_ns(file);
 		struct inode *inode = file_inode(file);
-		struct path_cond cond = { inode->i_uid, inode->i_mode };
+		struct path_cond cond = {
+			i_uid_into_mnt(mnt_userns, inode),
+			inode->i_mode
+		};
 
 		error = aa_path_perm(OP_OPEN, label, &file->f_path, 0,
 				     aa_map_file_to_perms(file), &cond);