[PATCH] generic acl support for ->permission

Currently we every filesystem with Posix ACLs has it's own reimplemtation
of the generic permission checking code with additonal ACL support.  This
patch

- adds an optional callback to vfs_permission that filesystems can use
  for ACL support (and renames it to generic_permission because the old
  name was wrong - it wasn't like the other vfs_* functions at all)

- uses it in ext2, ext3 and jfs.  XFS will follow a little later as it's
  permission checking is burried under several layers of abstraction.

From: Dave Kleikamp <shaggy@austin.ibm.com>

  jfs doesn't currently set MS_POSIXACL (it doesn't require the acl mount
  option), so this test would fail here.  The patch below will set it.
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

fs/cifs/CHANGES

@@ -7,8 +7,8 @@ or out of order NULL pointer checks in little used error paths).
 
 Version 1.21
 ------------
-Add new mount parm to control whether mode check (vfs_permission) is done on
-the client.  If Unix extensions are enabled and the uids on the client
+Add new mount parm to control whether mode check (generic_permission) is done
+on the client.  If Unix extensions are enabled and the uids on the client
 and server do not match, client permission checks are meaningless on
 server uids that do not exist on the client (this does not affect the
 normal ACL check which occurs on the server).  Fix default uid

fs/cifs/cifsfs.c

@@ -200,7 +200,7 @@ static int cifs_permission(struct inode * inode, int mask, struct nameidata *nd)
 		on the client (above and beyond ACL on servers) for  
 		servers which do not support setting and viewing mode bits,
 		so allowing client to check permissions is useful */ 
-		return vfs_permission(inode, mask);
+		return generic_permission(inode, mask, NULL);
 }
 
 static kmem_cache_t *cifs_inode_cachep;

fs/exec.c

@@ -886,7 +886,7 @@ int prepare_binprm(struct linux_binprm *bprm)
 	mode = inode->i_mode;
 	/*
 	 * Check execute perms again - if the caller has CAP_DAC_OVERRIDE,
-	 * vfs_permission lets a non-executable through
+	 * generic_permission lets a non-executable through
 	 */
 	if (!(mode & 0111))	/* with at least _one_ execute bit set */
 		return -EACCES;

fs/ext2/acl.c

@@ -280,60 +280,24 @@ ext2_set_acl(struct inode *inode, int type, struct posix_acl *acl)
 	return error;
 }
 
-/*
- * Inode operation permission().
- *
- * inode->i_sem: don't care
- */
-int
-ext2_permission(struct inode *inode, int mask, struct nameidata *nd)
+static int
+ext2_check_acl(struct inode *inode, int mask)
 {
-	int mode = inode->i_mode;
-
-	/* Nobody gets write access to a read-only fs */
-	if ((mask & MAY_WRITE) && IS_RDONLY(inode) &&
-	    (S_ISREG(mode) || S_ISDIR(mode) || S_ISLNK(mode)))
-		return -EROFS;
-	/* Nobody gets write access to an immutable file */
-	if ((mask & MAY_WRITE) && IS_IMMUTABLE(inode))
-	    return -EACCES;
-	if (current->fsuid == inode->i_uid) {
-		mode >>= 6;
-	} else if (test_opt(inode->i_sb, POSIX_ACL)) {
-		struct posix_acl *acl;
-
-		/* The access ACL cannot grant access if the group class
-		   permission bits don't contain all requested permissions. */
-		if (((mode >> 3) & mask & S_IRWXO) != mask)
-			goto check_groups;
-		acl = ext2_get_acl(inode, ACL_TYPE_ACCESS);
-		if (acl) {
-			int error = posix_acl_permission(inode, acl, mask);
-			posix_acl_release(acl);
-			if (error == -EACCES)
-				goto check_capabilities;
-			return error;
-		} else
-			goto check_groups;
-	} else {
-check_groups:
-		if (in_group_p(inode->i_gid))
-			mode >>= 3;
+	struct posix_acl *acl = ext2_get_acl(inode, ACL_TYPE_ACCESS);
+
+	if (acl) {
+		int error = posix_acl_permission(inode, acl, mask);
+		posix_acl_release(acl);
+		return error;
 	}
-	if ((mode & mask & S_IRWXO) == mask)
-		return 0;
 
-check_capabilities:
-	/* Allowed to override Discretionary Access Control? */
-	if (!(mask & MAY_EXEC) ||
-	    (inode->i_mode & S_IXUGO) || S_ISDIR(inode->i_mode))
-		if (capable(CAP_DAC_OVERRIDE))
-			return 0;
-	/* Read and search granted if capable(CAP_DAC_READ_SEARCH) */
-	if (capable(CAP_DAC_READ_SEARCH) && ((mask == MAY_READ) ||
-	    (S_ISDIR(inode->i_mode) && !(mask & MAY_WRITE))))
-		return 0;
-	return -EACCES;
+	return -EAGAIN;
+}
+
+int
+ext2_permission(struct inode *inode, int mask, struct nameidata *nd)
+{
+	return generic_permission(inode, mask, ext2_check_acl);
 }
 
 /*

fs/ext3/acl.c

@@ -285,60 +285,24 @@ ext3_set_acl(handle_t *handle, struct inode *inode, int type,
 	return error;
 }
 
-/*
- * Inode operation permission().
- *
- * inode->i_sem: don't care
- */
-int
-ext3_permission(struct inode *inode, int mask, struct nameidata *nd)
+static int
+ext3_check_acl(struct inode *inode, int mask)
 {
-	int mode = inode->i_mode;
-
-	/* Nobody gets write access to a read-only fs */
-	if ((mask & MAY_WRITE) && IS_RDONLY(inode) &&
-	    (S_ISREG(mode) || S_ISDIR(mode) || S_ISLNK(mode)))
-		return -EROFS;
-	/* Nobody gets write access to an immutable file */
-	if ((mask & MAY_WRITE) && IS_IMMUTABLE(inode))
-	    return -EACCES;
-	if (current->fsuid == inode->i_uid) {
-		mode >>= 6;
-	} else if (test_opt(inode->i_sb, POSIX_ACL)) {
-		struct posix_acl *acl;
-
-		/* The access ACL cannot grant access if the group class
-		   permission bits don't contain all requested permissions. */
-		if (((mode >> 3) & mask & S_IRWXO) != mask)
-			goto check_groups;
-		acl = ext3_get_acl(inode, ACL_TYPE_ACCESS);
-		if (acl) {
-			int error = posix_acl_permission(inode, acl, mask);
-			posix_acl_release(acl);
-			if (error == -EACCES)
-				goto check_capabilities;
-			return error;
-		} else
-			goto check_groups;
-	} else {
-check_groups:
-		if (in_group_p(inode->i_gid))
-			mode >>= 3;
+	struct posix_acl *acl = ext3_get_acl(inode, ACL_TYPE_ACCESS);
+
+	if (acl) {
+		int error = posix_acl_permission(inode, acl, mask);
+		posix_acl_release(acl);
+		return error;
 	}
-	if ((mode & mask & S_IRWXO) == mask)
-		return 0;
 
-check_capabilities:
-	/* Allowed to override Discretionary Access Control? */
-	if (!(mask & MAY_EXEC) ||
-	    (inode->i_mode & S_IXUGO) || S_ISDIR(inode->i_mode))
-		if (capable(CAP_DAC_OVERRIDE))
-			return 0;
-	/* Read and search granted if capable(CAP_DAC_READ_SEARCH) */
-	if (capable(CAP_DAC_READ_SEARCH) && ((mask == MAY_READ) ||
-	    (S_ISDIR(inode->i_mode) && !(mask & MAY_WRITE))))
-		return 0;
-	return -EACCES;
+	return -EAGAIN;
+}
+
+int
+ext3_permission(struct inode *inode, int mask, struct nameidata *nd)
+{
+	return generic_permission(inode, mask, ext3_check_acl);
 }
 
 /*

fs/hfs/inode.c

@@ -517,7 +517,7 @@ static int hfs_permission(struct inode *inode, int mask,
 {
 	if (S_ISREG(inode->i_mode) && mask & MAY_EXEC)
 		return 0;
-	return vfs_permission(inode, mask);
+	return generic_permission(inode, mask, NULL);
 }
 
 static int hfs_file_open(struct inode *inode, struct file *file)

fs/hfsplus/inode.c

@@ -260,7 +260,7 @@ static int hfsplus_permission(struct inode *inode, int mask, struct nameidata *n
 	 */
 	if (S_ISREG(inode->i_mode) && mask & MAY_EXEC && !(inode->i_mode & 0111))
 		return 0;
-	return vfs_permission(inode, mask);
+	return generic_permission(inode, mask, NULL);
 }
 
 

fs/hostfs/hostfs_kern.c

@@ -808,7 +808,7 @@ int hostfs_permission(struct inode *ino, int desired, struct nameidata *nd)
 	if(name == NULL) return(-ENOMEM);
 	err = access_file(name, r, w, x);
 	kfree(name);
-	if(!err) err = vfs_permission(ino, desired);
+	if(!err) err = generic_permission(ino, desired, NULL);
 	return(err);
 }
 

fs/jfs/acl.c

@@ -123,88 +123,25 @@ static int jfs_set_acl(struct inode *inode, int type, struct posix_acl *acl)
 	return rc;
 }
 
-/*
- *	jfs_permission()
- *
- * modified vfs_permission to check posix acl
- */
-int jfs_permission(struct inode * inode, int mask, struct nameidata *nd)
+static int jfs_check_acl(struct inode *inode, int mask)
 {
-	umode_t mode = inode->i_mode;
 	struct jfs_inode_info *ji = JFS_IP(inode);
 
-	if (mask & MAY_WRITE) {
-		/*
-		 * Nobody gets write access to a read-only fs.
-		 */
-		if (IS_RDONLY(inode) &&
-		    (S_ISREG(mode) || S_ISDIR(mode) || S_ISLNK(mode)))
-			return -EROFS;
-
-		/*
-		 * Nobody gets write access to an immutable file.
-		 */
-		if (IS_IMMUTABLE(inode))
-			return -EACCES;
-	}
-
-	if (current->fsuid == inode->i_uid) {
-		mode >>= 6;
-		goto check_mode;
-	}
-	/*
-	 * ACL can't contain additional permissions if the ACL_MASK entry
-	 * is zero.
-	 */
-	if (!(mode & S_IRWXG))
-		goto check_groups;
-
 	if (ji->i_acl == JFS_ACL_NOT_CACHED) {
-		struct posix_acl *acl;
-
-		acl = jfs_get_acl(inode, ACL_TYPE_ACCESS);
-
+		struct posix_acl *acl = jfs_get_acl(inode, ACL_TYPE_ACCESS);
 		if (IS_ERR(acl))
 			return PTR_ERR(acl);
 		posix_acl_release(acl);
 	}
 
-	if (ji->i_acl) {
-		int rc = posix_acl_permission(inode, ji->i_acl, mask);
-		if (rc == -EACCES)
-			goto check_capabilities;
-		return rc;
-	}
-
-check_groups:
-	if (in_group_p(inode->i_gid))
-		mode >>= 3;
-
-check_mode:
-	/*
-	 * If the DACs are ok we don't need any capability check.
-	 */
-	if (((mode & mask & (MAY_READ|MAY_WRITE|MAY_EXEC)) == mask))
-		return 0;
+	if (ji->i_acl)
+		return posix_acl_permission(inode, ji->i_acl, mask);
+	return -EAGAIN;
+}
 
-check_capabilities:
-	/*
-	 * Read/write DACs are always overridable.
-	 * Executable DACs are overridable if at least one exec bit is set.
-	 */
-	if (!(mask & MAY_EXEC) ||
-	    (inode->i_mode & S_IXUGO) || S_ISDIR(inode->i_mode))
-		if (capable(CAP_DAC_OVERRIDE))
-			return 0;
-
-	/*
-	 * Searching includes executable on directories, else just read.
-	 */
-	if (mask == MAY_READ || (S_ISDIR(inode->i_mode) && !(mask & MAY_WRITE)))
-		if (capable(CAP_DAC_READ_SEARCH))
-			return 0;
-
-	return -EACCES;
+int jfs_permission(struct inode *inode, int mask, struct nameidata *nd)
+{
+	return generic_permission(inode, mask, jfs_check_acl);
 }
 
 int jfs_init_acl(struct inode *inode, struct inode *dir)

fs/jfs/super.c

@@ -403,6 +403,10 @@ static int jfs_fill_super(struct super_block *sb, void *data, int silent)
 	}
 	sbi->flag = flag;
 
+#ifdef CONFIG_JFS_POSIX_ACL
+	sb->s_flags |= MS_POSIXACL;
+#endif
+
 	if (newLVSize) {
 		printk(KERN_ERR "resize option for remount only\n");
 		return -EINVAL;

fs/namei.c

@@ -152,15 +152,19 @@ char * getname(const char __user * filename)
 	return result;
 }
 
-/*
- *	vfs_permission()
+/**
+ * generic_permission  -  check for access rights on a Posix-like filesystem
+ * @inode:	inode to check access rights for
+ * @mask:	right to check for (%MAY_READ, %MAY_WRITE, %MAY_EXEC)
+ * @check_acl:	optional callback to check for Posix ACLs
  *
- * is used to check for read/write/execute permissions on a file.
+ * Used to check for read/write/execute permissions on a file.
  * We use "fsuid" for this, letting us set arbitrary permissions
  * for filesystem access without changing the "normal" uids which
  * are used for other things..
  */
-int vfs_permission(struct inode * inode, int mask)
+int generic_permission(struct inode *inode, int mask,
+		int (*check_acl)(struct inode *inode, int mask))
 {
 	umode_t			mode = inode->i_mode;
 
@@ -181,8 +185,18 @@ int vfs_permission(struct inode * inode, int mask)
 
 	if (current->fsuid == inode->i_uid)
 		mode >>= 6;
-	else if (in_group_p(inode->i_gid))
-		mode >>= 3;
+	else {
+		if (IS_POSIXACL(inode) && (mode & S_IRWXG) && check_acl) {
+			int error = check_acl(inode, mask);
+			if (error == -EACCES)
+				goto check_capabilities;
+			else if (error != -EAGAIN)
+				return error;
+		}
+
+		if (in_group_p(inode->i_gid))
+			mode >>= 3;
+	}
 
 	/*
 	 * If the DACs are ok we don't need any capability check.
@@ -190,6 +204,7 @@ int vfs_permission(struct inode * inode, int mask)
 	if (((mode & mask & (MAY_READ|MAY_WRITE|MAY_EXEC)) == mask))
 		return 0;
 
+ check_capabilities:
 	/*
 	 * Read/write DACs are always overridable.
 	 * Executable DACs are overridable if at least one exec bit is set.
@@ -220,7 +235,7 @@ int permission(struct inode * inode,int mask, struct nameidata *nd)
 	if (inode->i_op && inode->i_op->permission)
 		retval = inode->i_op->permission(inode, submask, nd);
 	else
-		retval = vfs_permission(inode, submask);
+		retval = generic_permission(inode, submask, NULL);
 	if (retval)
 		return retval;
 
@@ -315,7 +330,7 @@ static struct dentry * cached_lookup(struct dentry * parent, struct qstr * name,
 /*
  * Short-cut version of permission(), for calling by
  * path_walk(), when dcache lock is held.  Combines parts
- * of permission() and vfs_permission(), and tests ONLY for
+ * of permission() and generic_permission(), and tests ONLY for
  * MAY_EXEC permission.
  *
  * If appropriate, check DAC only.  If not appropriate, or
@@ -2456,7 +2471,7 @@ EXPORT_SYMBOL(vfs_follow_link);
 EXPORT_SYMBOL(vfs_link);
 EXPORT_SYMBOL(vfs_mkdir);
 EXPORT_SYMBOL(vfs_mknod);
-EXPORT_SYMBOL(vfs_permission);
+EXPORT_SYMBOL(generic_permission);
 EXPORT_SYMBOL(vfs_readlink);
 EXPORT_SYMBOL(vfs_rename);
 EXPORT_SYMBOL(vfs_rmdir);

fs/nfs/dir.c

@@ -1600,7 +1600,7 @@ int nfs_permission(struct inode *inode, int mask, struct nameidata *nd)
 	return res;
 out_notsup:
 	nfs_revalidate_inode(NFS_SERVER(inode), inode);
-	res = vfs_permission(inode, mask);
+	res = generic_permission(inode, mask, NULL);
 	unlock_kernel();
 	return res;
 }

fs/proc/base.c

@@ -473,7 +473,7 @@ static int proc_check_root(struct inode *inode)
 
 static int proc_permission(struct inode *inode, int mask, struct nameidata *nd)
 {
-	if (vfs_permission(inode, mask) != 0)
+	if (generic_permission(inode, mask, NULL) != 0)
 		return -EACCES;
 	return proc_check_root(inode);
 }

include/linux/fs.h

@@ -1339,7 +1339,9 @@ extern sector_t bmap(struct inode *, sector_t);
 extern int setattr_mask(unsigned int);
 extern int notify_change(struct dentry *, struct iattr *);
 extern int permission(struct inode *, int, struct nameidata *);
-extern int vfs_permission(struct inode *, int);
+extern int generic_permission(struct inode *, int,
+		int (*check_acl)(struct inode *, int));
+
 extern int get_write_access(struct inode *);
 extern int deny_write_access(struct file *);
 static inline void put_write_access(struct inode * inode)