exfat: handle idmapped mounts

Pass the idmapped mount information to the different helper
functions. Adapt the uid/gid checks in exfat_setattr to use the
vfsuid/vfsgid helpers.

Based on the fat implementation in commit 4b7899368108
("fat: handle idmapped mounts") by Christian Brauner.

Signed-off-by: Michael Jeanson <[email protected]>
Signed-off-by: Namjae Jeon <[email protected]>

file.c

@@ -99,12 +99,14 @@ static int exfat_cont_expand(struct inode *inode, loff_t size)
 	return -EIO;
 }
 
-static bool exfat_allow_set_time(struct exfat_sb_info *sbi, struct inode *inode)
+static bool exfat_allow_set_time(struct mnt_idmap *idmap,
+				struct exfat_sb_info *sbi, struct inode *inode)
 {
 	mode_t allow_utime = sbi->options.allow_utime;
 
-	if (!uid_eq(current_fsuid(), inode->i_uid)) {
-		if (in_group_p(inode->i_gid))
+	if (!vfsuid_eq_kuid(i_uid_into_vfsuid(idmap, inode),
+			    current_fsuid())) {
+		if (vfsgid_in_group_p(i_gid_into_vfsgid(idmap, inode)))
 			allow_utime >>= 3;
 		if (allow_utime & MAY_WRITE)
 			return true;
@@ -301,7 +303,7 @@ int exfat_getattr(struct user_namespace *mnt_uerns, const struct path *path,
 
 #if LINUX_VERSION_CODE >= KERNEL_VERSION(6, 3, 0)
 #if LINUX_VERSION_CODE >= KERNEL_VERSION(6, 6, 0)
-	generic_fillattr(&nop_mnt_idmap, request_mask, inode, stat);
+	generic_fillattr(idmap, request_mask, inode, stat);
 #else
 	generic_fillattr(&nop_mnt_idmap, inode, stat);
 #endif
@@ -340,13 +342,13 @@ int exfat_setattr(struct user_namespace *mnt_userns, struct dentry *dentry,
 	/* Check for setting the inode time. */
 	ia_valid = attr->ia_valid;
 	if ((ia_valid & (ATTR_MTIME_SET | ATTR_ATIME_SET | ATTR_TIMES_SET)) &&
-	    exfat_allow_set_time(sbi, inode)) {
+	    exfat_allow_set_time(idmap, sbi, inode)) {
 		attr->ia_valid &= ~(ATTR_MTIME_SET | ATTR_ATIME_SET |
 				ATTR_TIMES_SET);
 	}
 
 #if LINUX_VERSION_CODE >= KERNEL_VERSION(6, 3, 0)
-	error = setattr_prepare(&nop_mnt_idmap, dentry, attr);
+	error = setattr_prepare(idmap, dentry, attr);
 #else
 	error = setattr_prepare(&init_user_ns, dentry, attr);
 #endif
@@ -355,9 +357,11 @@ int exfat_setattr(struct user_namespace *mnt_userns, struct dentry *dentry,
 		goto out;
 
 	if (((attr->ia_valid & ATTR_UID) &&
-	     !uid_eq(attr->ia_uid, sbi->options.fs_uid)) ||
+	      (!uid_eq(from_vfsuid(idmap, i_user_ns(inode), attr->ia_vfsuid),
+	       sbi->options.fs_uid))) ||
 	    ((attr->ia_valid & ATTR_GID) &&
-	     !gid_eq(attr->ia_gid, sbi->options.fs_gid)) ||
+	      (!gid_eq(from_vfsgid(idmap, i_user_ns(inode), attr->ia_vfsgid),
+	       sbi->options.fs_gid))) ||
 	    ((attr->ia_valid & ATTR_MODE) &&
 	     (attr->ia_mode & ~(S_IFREG | S_IFLNK | S_IFDIR | 0777)))) {
 		error = -EPERM;
@@ -385,7 +389,7 @@ int exfat_setattr(struct user_namespace *mnt_userns, struct dentry *dentry,
 #endif
 
 #if LINUX_VERSION_CODE >= KERNEL_VERSION(6, 7, 0)
-	setattr_copy(&nop_mnt_idmap, inode, attr);
+	setattr_copy(idmap, inode, attr);
 	exfat_truncate_inode_atime(inode);
 #else
 #if LINUX_VERSION_CODE >= KERNEL_VERSION(6, 3, 0)

super.c

@@ -833,7 +833,7 @@ static struct file_system_type exfat_fs_type = {
 	.init_fs_context	= exfat_init_fs_context,
 	.parameters		= exfat_parameters,
 	.kill_sb		= exfat_kill_sb,
-	.fs_flags		= FS_REQUIRES_DEV,
+	.fs_flags		= FS_REQUIRES_DEV | FS_ALLOW_IDMAP,
 };
 
 static void exfat_inode_init_once(void *foo)