Patch "ovl: get_write_access() in truncate" has been added to the 4.6-stable tree

Patch "ovl: get_write_access() in truncate" has been added to the 4.6-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    ovl: get_write_access() in truncate

to the 4.6-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     ovl-get_write_access-in-truncate.patch
and it can be found in the queue-4.6 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 03bea60409328de54e4ff7ec41672e12a9cb0908 Mon Sep 17 00:00:00 2001
From: Miklos Szeredi <mszeredi@redhat.com>
Date: Wed, 29 Jun 2016 16:03:55 +0200
Subject: ovl: get_write_access() in truncate

From: Miklos Szeredi <mszeredi@redhat.com>

commit 03bea60409328de54e4ff7ec41672e12a9cb0908 upstream.

When truncating a file we should check write access on the underlying
inode.  And we should do so on the lower file as well (before copy-up) for
consistency.

Original patch and test case by Aihua Zhang.

 - - >o >o - - test.c - - >o >o - -
#include <stdio.h>
#include <errno.h>
#include <unistd.h>

int main(int argc, char *argv[])
{
	int ret;

	ret = truncate(argv[0], 4096);
	if (ret != -1) {
		fprintf(stderr, "truncate(argv[0]) should have failed\n");
		return 1;
	}
	if (errno != ETXTBSY) {
		perror("truncate(argv[0])");
		return 1;
	}

	return 0;
}
 - - >o >o - - >o >o - - >o >o - -

Reported-by: Aihua Zhang <zhangaihua1@huawei.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 fs/overlayfs/inode.c |   21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -59,16 +59,37 @@ int ovl_setattr(struct dentry *dentry, s
 	if (err)
 		goto out;
 
+	if (attr->ia_valid & ATTR_SIZE) {
+		struct inode *realinode = d_inode(ovl_dentry_real(dentry));
+
+		err = -ETXTBSY;
+		if (atomic_read(&realinode->i_writecount) < 0)
+			goto out_drop_write;
+	}
+
 	err = ovl_copy_up(dentry);
 	if (!err) {
+		struct inode *winode = NULL;
+
 		upperdentry = ovl_dentry_upper(dentry);
 
+		if (attr->ia_valid & ATTR_SIZE) {
+			winode = d_inode(upperdentry);
+			err = get_write_access(winode);
+			if (err)
+				goto out_drop_write;
+		}
+
 		inode_lock(upperdentry->d_inode);
 		err = notify_change(upperdentry, attr, NULL);
 		if (!err)
 			ovl_copyattr(upperdentry->d_inode, dentry->d_inode);
 		inode_unlock(upperdentry->d_inode);
+
+		if (winode)
+			put_write_access(winode);
 	}
+out_drop_write:
 	ovl_drop_write(dentry);
 out:
 	return err;


Patches currently in stable-queue which might be from mszeredi@redhat.com are

queue-4.6/ovl-copy-up-underlying-inode-s-i_mode-to-overlay-inode.patch
queue-4.6/ovl-verify-upper-dentry-in-ovl_remove_and_whiteout.patch
queue-4.6/ovl-fix-dentry-leak-for-default_permissions.patch
queue-4.6/ovl-get_write_access-in-truncate.patch
queue-4.6/ovl-handle-attr_kill.patch
queue-4.6/vfs-add-d_real_inode-helper.patch
queue-4.6/af_unix-fix-hard-linked-sockets-on-overlay.patch