Patch "ovl: drop CAP_SYS_RESOURCE from saved mounter's credentials" has been added to the 4.9-stable tree

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

ovl: drop CAP_SYS_RESOURCE from saved mounter's credentials

to the 4.9-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-drop-cap_sys_resource-from-saved-mounter-s-credentials.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Konstantin Khlebnikov <[email protected]>
Date: Tue, 10 Jan 2017 21:30:21 +0300
Subject: ovl: drop CAP_SYS_RESOURCE from saved mounter's credentials

From: Konstantin Khlebnikov <[email protected]>

commit 51f8f3c4e22535933ef9aecc00e9a6069e051b57 upstream.

If overlay was mounted by root then quota set for upper layer does not work because overlay now always use mounter's credentials for operations. Also overlay might deplete reserved space and inodes in ext4.

This patch drops capability SYS_RESOURCE from saved credentials. This affects creation new files, whiteouts, and copy-up operations.

---
 fs/overlayfs/super.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

@@ -1146,6 +1146,7 @@ static int ovl_fill_super(struct super_b
 	unsigned int stacklen = 0;
 	unsigned int i;
 	bool remote = false;
+	struct cred *cred;
 	int err;
 
 	err = -ENOMEM;

@@ -1309,10 +1310,13 @@ static int ovl_fill_super(struct super_b
 	else
 		sb->s_d_op = &ovl_dentry_operations;
 
-	ufs->creator_cred = prepare_creds();
-	if (!ufs->creator_cred)
+	ufs->creator_cred = cred = prepare_creds();
+	if (!cred)
 		goto out_put_lower_mnt;
 
+	/* Never override disk quota limits or use reserved space */
+	cap_lower(cred->cap_effective, CAP_SYS_RESOURCE);
+
 	err = -ENOMEM;
 	oe = ovl_alloc_entry(numlower);
 	if (!oe)

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/ovl-drop-cap_sys_resource-from-saved-mounter-s-credentials.patch