Patch "proc: Fix proc_sys_prune_dcache to hold a sb reference" has been added to the 4.11-stable tree

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

proc: Fix proc_sys_prune_dcache to hold a sb reference

to the 4.11-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:
proc-fix-proc_sys_prune_dcache-to-hold-a-sb-reference.patch
and it can be found in the queue-4.11 subdirectory.

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

From: "Eric W. Biederman" <[email protected]>
Date: Thu, 6 Jul 2017 08:41:06 -0500
Subject: proc: Fix proc_sys_prune_dcache to hold a sb reference

From: Eric W. Biederman <[email protected]>

commit 2fd1d2c4ceb2248a727696962cf3370dc9f5a0a4 upstream.

Andrei Vagin writes:
FYI: This bug has been reproduced on 4.11.7

Fix this by taking a reference to the super block in proc_sys_prune_dcache.

The superblock reference is the core of the fix however the sysctl_inodes list is converted to a hlist so that hlist_del_init_rcu may be used. This allows proc_sys_prune_dache to remove inodes the sysctl_inodes list, while not causing problems for proc_sys_evict_inode when if it later choses to remove the inode from the sysctl_inodes list. Removing inodes from the sysctl_inodes list allows proc_sys_prune_dcache to have a progress guarantee, while still being able to drop all locks. The fact that head->unregistering is set in start_unregistering ensures that no more inodes will be added to the the sysctl_inodes list.

Previously the code did a dance where it delayed calling iput until the next entry in the list was being considered to ensure the inode remained on the sysctl_inodes list until the next entry was walked to. The structure of the loop in this patch does not need that so is much easier to understand and maintain.

---
 fs/proc/internal.h     |    2 +-
 fs/proc/proc_sysctl.c  |   43 ++++++++++++++++++++++++++++++-------------
 include/linux/sysctl.h |    2 +-
 3 files changed, 32 insertions(+), 15 deletions(-)

@@ -67,7 +67,7 @@ struct proc_inode {
 	struct proc_dir_entry *pde;
 	struct ctl_table_header *sysctl;
 	struct ctl_table *sysctl_entry;
-	struct list_head sysctl_inodes;
+	struct hlist_node sysctl_inodes;
 	const struct proc_ns_operations *ns_ops;
 	struct inode vfs_inode;
 };

@@ -143,7 +143,7 @@ struct ctl_table_header
 	struct ctl_table_set *set;
 	struct ctl_dir *parent;
 	struct ctl_node *node;
-	struct list_head inodes; /* head for proc_inode->sysctl_inodes */
+	struct hlist_head inodes; /* head for proc_inode->sysctl_inodes */
 };
 
 struct ctl_dir {

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

queue-4.11/proc-fix-proc_sys_prune_dcache-to-hold-a-sb-reference.patch