[3.19.y-ckt stable] Patch "ovl: use a minimal buffer in ovl_copy_xattr" has been added to the 3.19.y-ckt tree

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    ovl: use a minimal buffer in ovl_copy_xattr

to the linux-3.19.y-queue branch of the 3.19.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.19.y-queue

This patch is scheduled to be released in version 3.19.8-ckt14.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.19.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

---8<------------------------------------------------------------

>From a541b8ac0db45832449213b7973507d6cce5ebd3 Mon Sep 17 00:00:00 2001
From: Vito Caputo <vito.caputo at coreos.com>
Date: Sat, 24 Oct 2015 07:19:46 -0500
Subject: ovl: use a minimal buffer in ovl_copy_xattr

commit e4ad29fa0d224d05e08b2858e65f112fd8edd4fe upstream.

Rather than always allocating the high-order XATTR_SIZE_MAX buffer
which is costly and prone to failure, only allocate what is needed and
realloc if necessary.

Fixes https://github.com/coreos/bugs/issues/489

Signed-off-by: Miklos Szeredi <miklos at szeredi.hu>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 fs/overlayfs/copy_up.c | 39 +++++++++++++++++++++++++--------------
 1 file changed, 25 insertions(+), 14 deletions(-)

diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
index 37b1b9e..76c1460 100644
--- a/fs/overlayfs/copy_up.c
+++ b/fs/overlayfs/copy_up.c
@@ -22,9 +22,9 @@

 int ovl_copy_xattr(struct dentry *old, struct dentry *new)
 {
-	ssize_t list_size, size;
-	char *buf, *name, *value;
-	int error;
+	ssize_t list_size, size, value_size = 0;
+	char *buf, *name, *value = NULL;
+	int uninitialized_var(error);

 	if (!old->d_inode->i_op->getxattr ||
 	    !new->d_inode->i_op->getxattr)
@@ -41,29 +41,40 @@ int ovl_copy_xattr(struct dentry *old, struct dentry *new)
 	if (!buf)
 		return -ENOMEM;

-	error = -ENOMEM;
-	value = kmalloc(XATTR_SIZE_MAX, GFP_KERNEL);
-	if (!value)
-		goto out;
-
 	list_size = vfs_listxattr(old, buf, list_size);
 	if (list_size <= 0) {
 		error = list_size;
-		goto out_free_value;
+		goto out;
 	}

 	for (name = buf; name < (buf + list_size); name += strlen(name) + 1) {
-		size = vfs_getxattr(old, name, value, XATTR_SIZE_MAX);
+retry:
+		size = vfs_getxattr(old, name, value, value_size);
+		if (size == -ERANGE)
+			size = vfs_getxattr(old, name, NULL, 0);
+
 		if (size < 0) {
 			error = size;
-			goto out_free_value;
+			break;
+		}
+
+		if (size > value_size) {
+			void *new;
+
+			new = krealloc(value, size, GFP_KERNEL);
+			if (!new) {
+				error = -ENOMEM;
+				break;
+			}
+			value = new;
+			value_size = size;
+			goto retry;
 		}
+
 		error = vfs_setxattr(new, name, value, size, 0);
 		if (error)
-			goto out_free_value;
+			break;
 	}
-
-out_free_value:
 	kfree(value);
 out:
 	kfree(buf);
--
1.9.1