Date: Mon, 17 Feb 2020 15:50:28 -0600
From: Pete Zaitcev <zaitcev@kotori.zaitcev.us>
To: linux-mm@kvack.org
Cc: Pete Zaitcev <zaitcev@kotori.zaitcev.us>, Helge Deller <deller@gmx.de>,
 Hugh Dickins <hughd@google.com>
Subject: [patch] fs: Allow user.* xattr in tmpfs
Message-ID: <20200217155028.632662af@suzdal.zaitcev.lan>
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Envelope-To: <deller@gmx.de>

Not having xattr in /tmp can be worked around usually by configuring
the affected software with TMPDIR=/var/tmp and the like, but I prefer
having this automated, if possible.

Signed-off-by: Pete Zaitcev <zaitcev@yahoo.com>
---
 fs/xattr.c            |    3 +++
 include/linux/xattr.h |   13 +++++++++++++
 mm/shmem.c            |   25 +++++++++++++++++++++++++
 3 files changed, 41 insertions(+)

diff --git a/fs/xattr.c b/fs/xattr.c
index 90dd78f0eb27..502567a4a478 100644
--- a/fs/xattr.c
+++ b/fs/xattr.c
@@ -896,6 +896,7 @@ int simple_xattr_set(struct simple_xattrs *xattrs, const char *name,
 			} else if (new_xattr) {
 				list_replace(&xattr->list, &new_xattr->list);
 			} else {
+				--xattrs->count;
 				list_del(&xattr->list);
 			}
 			goto out;
@@ -906,6 +907,7 @@ int simple_xattr_set(struct simple_xattrs *xattrs, const char *name,
 		err = -ENODATA;
 	} else {
 		list_add(&new_xattr->list, &xattrs->head);
+		xattrs->count++;
 		xattr = NULL;
 	}
 out:
@@ -988,5 +990,6 @@ void simple_xattr_list_add(struct simple_xattrs *xattrs,
 {
 	spin_lock(&xattrs->lock);
 	list_add(&new_xattr->list, &xattrs->head);
+	xattrs->count++;
 	spin_unlock(&xattrs->lock);
 }
diff --git a/include/linux/xattr.h b/include/linux/xattr.h
index 6dad031be3c2..e1ed5910ef5c 100644
--- a/include/linux/xattr.h
+++ b/include/linux/xattr.h
@@ -67,6 +67,7 @@ static inline const char *xattr_prefix(const struct xattr_handler *handler)
 struct simple_xattrs {
 	struct list_head head;
 	spinlock_t lock;
+	int count;
 };
 
 struct simple_xattr {
@@ -83,6 +84,7 @@ static inline void simple_xattrs_init(struct simple_xattrs *xattrs)
 {
 	INIT_LIST_HEAD(&xattrs->head);
 	spin_lock_init(&xattrs->lock);
+	xattrs->count = 0;
 }
 
 /*
@@ -96,6 +98,17 @@ static inline void simple_xattrs_free(struct simple_xattrs *xattrs)
 		kfree(xattr->name);
 		kfree(xattr);
 	}
+	xattrs->count = 0;
+}
+
+static inline int simple_xattrs_count(struct simple_xattrs *xattrs)
+{
+	int ret;
+
+	spin_lock(&xattrs->lock);
+	ret = xattrs->count;
+	spin_unlock(&xattrs->lock);
+	return ret;
 }
 
 struct simple_xattr *simple_xattr_alloc(const void *value, size_t size);
diff --git a/mm/shmem.c b/mm/shmem.c
index c8f7540ef048..0ce17afad30e 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -3246,6 +3246,30 @@ static int shmem_xattr_handler_set(const struct xattr_handler *handler,
 	return simple_xattr_set(&info->xattrs, name, value, size, flags);
 }
 
+static int shmem_xattr_handler_set_user(const struct xattr_handler *handler,
+				   struct dentry *unused, struct inode *inode,
+				   const char *name, const void *value,
+				   size_t size, int flags)
+{
+	struct shmem_inode_info *info = SHMEM_I(inode);
+	struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
+
+	if (value) {
+		if (size > 8192)
+			return -EINVAL;
+		if (simple_xattrs_count(&info->xattrs) >= sbinfo->max_inodes)
+			return -ENOSPC;
+	}
+	name = xattr_full_name(handler, name);
+	return simple_xattr_set(&info->xattrs, name, value, size, flags, NULL);
+}
+
+static const struct xattr_handler shmem_user_xattr_handler = {
+	.prefix = XATTR_USER_PREFIX,
+	.get = shmem_xattr_handler_get,
+	.set = shmem_xattr_handler_set_user,
+};
+
 static const struct xattr_handler shmem_security_xattr_handler = {
 	.prefix = XATTR_SECURITY_PREFIX,
 	.get = shmem_xattr_handler_get,
@@ -3263,6 +3287,7 @@ static const struct xattr_handler *shmem_xattr_handlers[] = {
 	&posix_acl_access_xattr_handler,
 	&posix_acl_default_xattr_handler,
 #endif
+	&shmem_user_xattr_handler,
 	&shmem_security_xattr_handler,
 	&shmem_trusted_xattr_handler,
 	NULL