Commit 41a0ecc0 authored by Al Viro's avatar Al Viro Committed by Greg Kroah-Hartman
Browse files

debugfs: get rid of dynamically allocation proxy_ops 



All it takes is having full_proxy_open() collect the information
about available methods and store it in debugfs_fsdata.

Wrappers are called only after full_proxy_open() has succeeded
calling debugfs_get_file(), so they are guaranteed to have
->d_fsdata already pointing to debugfs_fsdata.

As the result, they can check if method is absent and bugger off
early, without any atomic operations, etc. - same effect as what
we'd have from NULL method.  Which makes the entire proxy_fops
contents unconditional, making it completely pointless - we can
just put those methods (unconditionally) into
debugfs_full_proxy_file_operations and forget about dynamic
allocation, replace_fops, etc.

Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
Reviewed-by: default avatarChristian Brauner <brauner@kernel.org>
Link: https://lore.kernel.org/r/20250112080705.141166-3-viro@zeniv.linux.org.uk


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent bacaaf83

fs/debugfs/file.c

+52 −61
Original line number Diff line number Diff line
@@ -95,13 +95,31 @@ static int __debugfs_file_get(struct dentry *dentry, enum dbgfs_get_mode mode) 
			return -ENOMEM;



		if (mode == DBGFS_GET_SHORT) {

			fsd->real_fops = NULL;

			fsd->short_fops = (void *)((unsigned long)d_fsd &

			const struct debugfs_short_fops *ops;

			ops = (void *)((unsigned long)d_fsd &

					~DEBUGFS_FSDATA_IS_REAL_FOPS_BIT);

			fsd->short_fops = ops;

			if (ops->llseek)

				fsd->methods |= HAS_LSEEK;

			if (ops->read)

				fsd->methods |= HAS_READ;

			if (ops->write)

				fsd->methods |= HAS_WRITE;

		} else {

			fsd->real_fops = (void *)((unsigned long)d_fsd &

			const struct file_operations *ops;

			ops = (void *)((unsigned long)d_fsd &

					~DEBUGFS_FSDATA_IS_REAL_FOPS_BIT);

			fsd->short_fops = NULL;

			fsd->real_fops = ops;

			if (ops->llseek)

				fsd->methods |= HAS_LSEEK;

			if (ops->read)

				fsd->methods |= HAS_READ;

			if (ops->write)

				fsd->methods |= HAS_WRITE;

			if (ops->unlocked_ioctl)

				fsd->methods |= HAS_IOCTL;

			if (ops->poll)

				fsd->methods |= HAS_POLL;

		}

		refcount_set(&fsd->active_users, 1);

		init_completion(&fsd->active_users_drained);
@@ -322,13 +340,16 @@ const struct file_operations debugfs_open_proxy_file_operations = { 
#define PROTO(args...) args

#define ARGS(args...) args



#define FULL_PROXY_FUNC(name, ret_type, filp, proto, args)		\

#define FULL_PROXY_FUNC(name, ret_type, filp, proto, args, bit, ret)	\

static ret_type full_proxy_ ## name(proto)				\

{									\

	struct dentry *dentry = F_DENTRY(filp);				\

	struct debugfs_fsdata *fsd = dentry->d_fsdata;			\

	const struct file_operations *real_fops;			\

	ret_type r;							\

									\

	if (!(fsd->methods & bit))					\

		return ret;						\

	r = debugfs_file_get(dentry);					\

	if (unlikely(r))						\

		return r;						\
@@ -338,17 +359,18 @@ static ret_type full_proxy_ ## name(proto) \ 
	return r;							\

}



#define FULL_PROXY_FUNC_BOTH(name, ret_type, filp, proto, args)		\

#define FULL_PROXY_FUNC_BOTH(name, ret_type, filp, proto, args, bit, ret)	\

static ret_type full_proxy_ ## name(proto)				\

{									\

	struct dentry *dentry = F_DENTRY(filp);				\

	struct debugfs_fsdata *fsd;					\

	struct debugfs_fsdata *fsd = dentry->d_fsdata;			\

	ret_type r;							\

									\

	if (!(fsd->methods & bit))					\

		return ret;						\

	r = debugfs_file_get(dentry);					\

	if (unlikely(r))						\

		return r;						\

	fsd = dentry->d_fsdata;						\

	if (fsd->real_fops)						\

		r = fsd->real_fops->name(args);				\

	else								\
@@ -359,29 +381,32 @@ static ret_type full_proxy_ ## name(proto) \ 


FULL_PROXY_FUNC_BOTH(llseek, loff_t, filp,

		     PROTO(struct file *filp, loff_t offset, int whence),

		     ARGS(filp, offset, whence));

		     ARGS(filp, offset, whence), HAS_LSEEK, -ESPIPE);



FULL_PROXY_FUNC_BOTH(read, ssize_t, filp,

		     PROTO(struct file *filp, char __user *buf, size_t size,

			   loff_t *ppos),

		     ARGS(filp, buf, size, ppos));

		     ARGS(filp, buf, size, ppos), HAS_READ, -EINVAL);



FULL_PROXY_FUNC_BOTH(write, ssize_t, filp,

		     PROTO(struct file *filp, const char __user *buf,

			   size_t size, loff_t *ppos),

		     ARGS(filp, buf, size, ppos));

		     ARGS(filp, buf, size, ppos), HAS_WRITE, -EINVAL);



FULL_PROXY_FUNC(unlocked_ioctl, long, filp,

		PROTO(struct file *filp, unsigned int cmd, unsigned long arg),

		ARGS(filp, cmd, arg));

		ARGS(filp, cmd, arg), HAS_IOCTL, -ENOTTY);



static __poll_t full_proxy_poll(struct file *filp,

				struct poll_table_struct *wait)

{

	struct dentry *dentry = F_DENTRY(filp);

	struct debugfs_fsdata *fsd = dentry->d_fsdata;

	__poll_t r = 0;

	const struct file_operations *real_fops;



	if (!(fsd->methods & HAS_POLL))

		return DEFAULT_POLLMASK;

	if (debugfs_file_get(dentry))

		return EPOLLHUP;
@@ -393,9 +418,7 @@ static __poll_t full_proxy_poll(struct file *filp, 


static int full_proxy_release(struct inode *inode, struct file *filp)

{

	const struct dentry *dentry = F_DENTRY(filp);

	const struct file_operations *real_fops = debugfs_real_fops(filp);

	const struct file_operations *proxy_fops = filp->f_op;

	int r = 0;



	/*
@@ -407,42 +430,15 @@ static int full_proxy_release(struct inode *inode, struct file *filp) 
	if (real_fops && real_fops->release)

		r = real_fops->release(inode, filp);



	replace_fops(filp, d_inode(dentry)->i_fop);

	kfree(proxy_fops);

	fops_put(real_fops);

	return r;

}



static void __full_proxy_fops_init(struct file_operations *proxy_fops,

				   struct debugfs_fsdata *fsd)

{

	proxy_fops->release = full_proxy_release;



	if ((fsd->real_fops && fsd->real_fops->llseek) ||

	    (fsd->short_fops && fsd->short_fops->llseek))

		proxy_fops->llseek = full_proxy_llseek;



	if ((fsd->real_fops && fsd->real_fops->read) ||

	    (fsd->short_fops && fsd->short_fops->read))

		proxy_fops->read = full_proxy_read;



	if ((fsd->real_fops && fsd->real_fops->write) ||

	    (fsd->short_fops && fsd->short_fops->write))

		proxy_fops->write = full_proxy_write;



	if (fsd->real_fops && fsd->real_fops->poll)

		proxy_fops->poll = full_proxy_poll;



	if (fsd->real_fops && fsd->real_fops->unlocked_ioctl)

		proxy_fops->unlocked_ioctl = full_proxy_unlocked_ioctl;

}



static int full_proxy_open(struct inode *inode, struct file *filp,

			   enum dbgfs_get_mode mode)

{

	struct dentry *dentry = F_DENTRY(filp);

	const struct file_operations *real_fops;

	struct file_operations *proxy_fops = NULL;

	struct debugfs_fsdata *fsd;

	int r;
@@ -472,34 +468,20 @@ static int full_proxy_open(struct inode *inode, struct file *filp, 
		goto out;

	}



	proxy_fops = kzalloc(sizeof(*proxy_fops), GFP_KERNEL);

	if (!proxy_fops) {

		r = -ENOMEM;

		goto free_proxy;

	}

	__full_proxy_fops_init(proxy_fops, fsd);

	replace_fops(filp, proxy_fops);



	if (!real_fops || real_fops->open) {

		if (real_fops)

			r = real_fops->open(inode, filp);

		else

			r = simple_open(inode, filp);

		if (r) {

			replace_fops(filp, d_inode(dentry)->i_fop);

			goto free_proxy;

		} else if (filp->f_op != proxy_fops) {

			fops_put(real_fops);

		} else if (filp->f_op != &debugfs_full_proxy_file_operations) {

			/* No protection against file removal anymore. */

			WARN(1, "debugfs file owner replaced proxy fops: %pd",

				dentry);

			goto free_proxy;

			fops_put(real_fops);

		}

	}



	goto out;

free_proxy:

	kfree(proxy_fops);

	fops_put(real_fops);

out:

	debugfs_file_put(dentry);

	return r;
@@ -512,6 +494,12 @@ static int full_proxy_open_regular(struct inode *inode, struct file *filp) 


const struct file_operations debugfs_full_proxy_file_operations = {

	.open = full_proxy_open_regular,

	.release = full_proxy_release,

	.llseek = full_proxy_llseek,

	.read = full_proxy_read,

	.write = full_proxy_write,

	.poll = full_proxy_poll,

	.unlocked_ioctl = full_proxy_unlocked_ioctl

};



static int full_proxy_open_short(struct inode *inode, struct file *filp)
@@ -521,6 +509,9 @@ static int full_proxy_open_short(struct inode *inode, struct file *filp) 


const struct file_operations debugfs_full_short_proxy_file_operations = {

	.open = full_proxy_open_short,

	.llseek = full_proxy_llseek,

	.read = full_proxy_read,

	.write = full_proxy_write,

};



ssize_t debugfs_attr_read(struct file *file, char __user *buf,

fs/debugfs/internal.h

+9 −0
Original line number Diff line number Diff line
@@ -39,9 +39,18 @@ struct debugfs_fsdata { 
		/* protect cancellations */

		struct mutex cancellations_mtx;

		struct list_head cancellations;

		unsigned int methods;

	};

};



enum {

	HAS_READ = 1,

	HAS_WRITE = 2,

	HAS_LSEEK = 4,

	HAS_POLL = 8,

	HAS_IOCTL = 16

};



/*

 * A dentry's ->d_fsdata either points to the real fops or to a

 * dynamically allocated debugfs_fsdata instance.