Commit dfef6dcd authored by Al Viro's avatar Al Viro
Browse files

unfuck proc_sysctl ->d_compare() 



a) struct inode is not going to be freed under ->d_compare();
however, the thing PROC_I(inode)->sysctl points to just might.
Fortunately, it's enough to make freeing that sucker delayed,
provided that we don't step on its ->unregistering, clear
the pointer to it in PROC_I(inode) before dropping the reference
and check if it's NULL in ->d_compare().

b) I'm not sure that we *can* walk into NULL inode here (we recheck
dentry->seq between verifying that it's still hashed / fetching
dentry->d_inode and passing it to ->d_compare() and there's no
negative hashed dentries in /proc/sys/*), but if we can walk into
that, we really should not have ->d_compare() return 0 on it!
Said that, I really suspect that this check can be simply killed.
Nick?

Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 1858efd4

fs/proc/inode.c

+6 −2
Original line number Diff line number Diff line
@@ -27,6 +27,7 @@ 
static void proc_evict_inode(struct inode *inode)

{

	struct proc_dir_entry *de;

	struct ctl_table_header *head;



	truncate_inode_pages(&inode->i_data, 0);

	end_writeback(inode);
@@ -38,8 +39,11 @@ static void proc_evict_inode(struct inode *inode) 
	de = PROC_I(inode)->pde;

	if (de)

		pde_put(de);

	if (PROC_I(inode)->sysctl)

		sysctl_head_put(PROC_I(inode)->sysctl);

	head = PROC_I(inode)->sysctl;

	if (head) {

		rcu_assign_pointer(PROC_I(inode)->sysctl, NULL);

		sysctl_head_put(head);

	}

}



struct vfsmount *proc_mnt;

fs/proc/proc_sysctl.c

+5 −2
Original line number Diff line number Diff line
@@ -408,15 +408,18 @@ static int proc_sys_compare(const struct dentry *parent, 
		const struct dentry *dentry, const struct inode *inode,

		unsigned int len, const char *str, const struct qstr *name)

{

	struct ctl_table_header *head;

	/* Although proc doesn't have negative dentries, rcu-walk means

	 * that inode here can be NULL */

	/* AV: can it, indeed? */

	if (!inode)

		return 0;

		return 1;

	if (name->len != len)

		return 1;

	if (memcmp(name->name, str, len))

		return 1;

	return !sysctl_is_seen(PROC_I(inode)->sysctl);

	head = rcu_dereference(PROC_I(inode)->sysctl);

	return !head || !sysctl_is_seen(head);

}



static const struct dentry_operations proc_sys_dentry_operations = {

include/linux/sysctl.h

+10 −4
Original line number Diff line number Diff line
@@ -25,6 +25,7 @@ 
#include <linux/kernel.h>

#include <linux/types.h>

#include <linux/compiler.h>

#include <linux/rcupdate.h>



struct completion;
@@ -1037,10 +1038,15 @@ struct ctl_table_root { 
   struct ctl_table trees. */

struct ctl_table_header

{

	union {

		struct {

			struct ctl_table *ctl_table;

			struct list_head ctl_entry;

			int used;

			int count;

		};

		struct rcu_head rcu;

	};

	struct completion *unregistering;

	struct ctl_table *ctl_table_arg;

	struct ctl_table_root *root;

kernel/sysctl.c

+10 −5
Original line number Diff line number Diff line
@@ -194,9 +194,9 @@ static int sysrq_sysctl_handler(ctl_table *table, int write, 
static struct ctl_table root_table[];

static struct ctl_table_root sysctl_table_root;

static struct ctl_table_header root_table_header = {

	.count = 1,

	{{.count = 1,

	.ctl_table = root_table,

	.ctl_entry = LIST_HEAD_INIT(sysctl_table_root.default_set.list),

	.ctl_entry = LIST_HEAD_INIT(sysctl_table_root.default_set.list),}},

	.root = &sysctl_table_root,

	.set = &sysctl_table_root.default_set,

};
@@ -1567,11 +1567,16 @@ void sysctl_head_get(struct ctl_table_header *head) 
	spin_unlock(&sysctl_lock);

}



static void free_head(struct rcu_head *rcu)

{

	kfree(container_of(rcu, struct ctl_table_header, rcu));

}



void sysctl_head_put(struct ctl_table_header *head)

{

	spin_lock(&sysctl_lock);

	if (!--head->count)

		kfree(head);

		call_rcu(&head->rcu, free_head);

	spin_unlock(&sysctl_lock);

}
@@ -1948,10 +1953,10 @@ void unregister_sysctl_table(struct ctl_table_header * header) 
	start_unregistering(header);

	if (!--header->parent->count) {

		WARN_ON(1);

		kfree(header->parent);

		call_rcu(&header->parent->rcu, free_head);

	}

	if (!--header->count)

		kfree(header);

		call_rcu(&header->rcu, free_head);

	spin_unlock(&sysctl_lock);

}

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