/* SPDX-License-Identifier: GPL-2.0 */#include <linux/syscalls.h>#include <linux/export.h>#include <linux/uaccess.h>#include <linux/fs_struct.h>#include <linux/fs.h>#include <linux/slab.h>#include <linux/prefetch.h>#include "mount.h" static int prepend(char **buffer, int *buflen, const char *str, int namelen){	*buflen -= namelen;	if (*buflen < 0)		return -ENAMETOOLONG;	*buffer -= namelen;	memcpy(*buffer, str, namelen);	return 0;} /** * prepend_name - prepend a pathname in front of current buffer pointer * @buffer: buffer pointer * @buflen: allocated length of the buffer * @name:   name string and length qstr structure * * With RCU path tracing, it may race with d_move(). Use READ_ONCE() to * make sure that either the old or the new name pointer and length are * fetched. However, there may be mismatch between length and pointer. * The length cannot be trusted, we need to copy it byte-by-byte until * the length is reached or a null byte is found. It also prepends "/" at * the beginning of the name. The sequence number check at the caller will * retry it again when a d_move() does happen. So any garbage in the buffer * due to mismatched pointer and length will be discarded. * * Load acquire is needed to make sure that we see that terminating NUL. */static int prepend_name(char **buffer, int *buflen, const struct qstr *name){	const char *dname = smp_load_acquire(&name->name); /* ^^^ */	u32 dlen = READ_ONCE(name->len);	char *p; 	*buflen -= dlen + 1;	if (*buflen < 0)		return -ENAMETOOLONG;	p = *buffer -= dlen + 1;	*p++ = '/';	while (dlen--) {		char c = *dname++;		if (!c)			break;		*p++ = c;	}	return 0;} /** * prepend_path - Prepend path string to a buffer * @path: the dentry/vfsmount to report * @root: root vfsmnt/dentry * @buffer: pointer to the end of the buffer * @buflen: pointer to buffer length * * The function will first try to write out the pathname without taking any * lock other than the RCU read lock to make sure that dentries won't go away. * It only checks the sequence number of the global rename_lock as any change * in the dentry's d_seq will be preceded by changes in the rename_lock * sequence number. If the sequence number had been changed, it will restart * the whole pathname back-tracing sequence again by taking the rename_lock. * In this case, there is no need to take the RCU read lock as the recursive * parent pointer references will keep the dentry chain alive as long as no * rename operation is performed. */static int prepend_path(const struct path *path,			const struct path *root,			char **buffer, int *buflen){	struct dentry *dentry;	struct vfsmount *vfsmnt;	struct mount *mnt;	int error = 0;	unsigned seq, m_seq = 0;	char *bptr;	int blen; 	rcu_read_lock();restart_mnt:	read_seqbegin_or_lock(&mount_lock, &m_seq);	seq = 0;	rcu_read_lock();restart:	bptr = *buffer;	blen = *buflen;	error = 0;	dentry = path->dentry;	vfsmnt = path->mnt;	mnt = real_mount(vfsmnt);	read_seqbegin_or_lock(&rename_lock, &seq);	while (dentry != root->dentry || vfsmnt != root->mnt) {		struct dentry * parent; 		if (dentry == vfsmnt->mnt_root || IS_ROOT(dentry)) {			struct mount *parent = READ_ONCE(mnt->mnt_parent);			/* Escaped? */			if (dentry != vfsmnt->mnt_root) {				bptr = *buffer;				blen = *buflen;				error = 3;				break;			}			/* Global root? */			if (mnt != parent) {				dentry = READ_ONCE(mnt->mnt_mountpoint);				mnt = parent;				vfsmnt = &mnt->mnt;				continue;			}			if (is_mounted(vfsmnt) && !is_anon_ns(mnt->mnt_ns))				error = 1;	// absolute root			else				error = 2;	// detached or not attached yet			break;		}		parent = dentry->d_parent;		prefetch(parent);		error = prepend_name(&bptr, &blen, &dentry->d_name);		if (error)			break; 		dentry = parent;	}	if (!(seq & 1))		rcu_read_unlock();	if (need_seqretry(&rename_lock, seq)) {		seq = 1;		goto restart;	}	done_seqretry(&rename_lock, seq); 	if (!(m_seq & 1))		rcu_read_unlock();	if (need_seqretry(&mount_lock, m_seq)) {		m_seq = 1;		goto restart_mnt;	}	done_seqretry(&mount_lock, m_seq); 	if (error >= 0 && bptr == *buffer) {		if (--blen < 0)			error = -ENAMETOOLONG;		else			*--bptr = '/';	}	*buffer = bptr;	*buflen = blen;	return error;} /** * __d_path - return the path of a dentry * @path: the dentry/vfsmount to report * @root: root vfsmnt/dentry * @buf: buffer to return value in * @buflen: buffer length * * Convert a dentry into an ASCII path name. * * Returns a pointer into the buffer or an error code if the * path was too long. * * "buflen" should be positive. * * If the path is not reachable from the supplied root, return %NULL. */char *__d_path(const struct path *path,	       const struct path *root,	       char *buf, int buflen){	char *res = buf + buflen;	int error; 	prepend(&res, &buflen, "\0", 1);	error = prepend_path(path, root, &res, &buflen); 	if (error < 0)		return ERR_PTR(error);	if (error > 0)		return NULL;	return res;} char *d_absolute_path(const struct path *path,	       char *buf, int buflen){	struct path root = {};	char *res = buf + buflen;	int error; 	prepend(&res, &buflen, "\0", 1);	error = prepend_path(path, &root, &res, &buflen); 	if (error > 1)		error = -EINVAL;	if (error < 0)		return ERR_PTR(error);	return res;} /* * same as __d_path but appends "(deleted)" for unlinked files. */static int path_with_deleted(const struct path *path,			     const struct path *root,			     char **buf, int *buflen){	prepend(buf, buflen, "\0", 1);	if (d_unlinked(path->dentry)) {		int error = prepend(buf, buflen, " (deleted)", 10);		if (error)			return error;	} 	return prepend_path(path, root, buf, buflen);} static int prepend_unreachable(char **buffer, int *buflen){	return prepend(buffer, buflen, "(unreachable)", 13);} static void get_fs_root_rcu(struct fs_struct *fs, struct path *root){	unsigned seq; 	do {		seq = read_seqcount_begin(&fs->seq);		*root = fs->root;	} while (read_seqcount_retry(&fs->seq, seq));} /** * d_path - return the path of a dentry * @path: path to report * @buf: buffer to return value in * @buflen: buffer length * * Convert a dentry into an ASCII path name. If the entry has been deleted * the string " (deleted)" is appended. Note that this is ambiguous. * * Returns a pointer into the buffer or an error code if the path was * too long. Note: Callers should use the returned pointer, not the passed * in buffer, to use the name! The implementation often starts at an offset * into the buffer, and may leave 0 bytes at the start. * * "buflen" should be positive. */char *d_path(const struct path *path, char *buf, int buflen){	char *res = buf + buflen;	struct path root;	int error; 	/*	 * We have various synthetic filesystems that never get mounted.  On	 * these filesystems dentries are never used for lookup purposes, and	 * thus don't need to be hashed.  They also don't need a name until a	 * user wants to identify the object in /proc/pid/fd/.  The little hack	 * below allows us to generate a name for these objects on demand:	 *	 * Some pseudo inodes are mountable.  When they are mounted	 * path->dentry == path->mnt->mnt_root.  In that case don't call d_dname	 * and instead have d_path return the mounted path.	 */	if (path->dentry->d_op && path->dentry->d_op->d_dname &&	    (!IS_ROOT(path->dentry) || path->dentry != path->mnt->mnt_root))		return path->dentry->d_op->d_dname(path->dentry, buf, buflen); 	rcu_read_lock();	get_fs_root_rcu(current->fs, &root);	error = path_with_deleted(path, &root, &res, &buflen);	rcu_read_unlock(); 	if (error < 0)		res = ERR_PTR(error);	return res;}EXPORT_SYMBOL(d_path); /* * Helper function for dentry_operations.d_dname() members */char *dynamic_dname(struct dentry *dentry, char *buffer, int buflen,			const char *fmt, ...){	va_list args;	char temp[64];	int sz; 	va_start(args, fmt);	sz = vsnprintf(temp, sizeof(temp), fmt, args) + 1;	va_end(args); 	if (sz > sizeof(temp) || sz > buflen)		return ERR_PTR(-ENAMETOOLONG); 	buffer += buflen - sz;	return memcpy(buffer, temp, sz);} char *simple_dname(struct dentry *dentry, char *buffer, int buflen){	char *end = buffer + buflen;	/* these dentries are never renamed, so d_lock is not needed */	if (prepend(&end, &buflen, " (deleted)", 11) ||	    prepend(&end, &buflen, dentry->d_name.name, dentry->d_name.len) ||	    prepend(&end, &buflen, "/", 1))  		end = ERR_PTR(-ENAMETOOLONG);	return end;} /* * Write full pathname from the root of the filesystem into the buffer. */static char *__dentry_path(struct dentry *d, char *buf, int buflen){	struct dentry *dentry;	char *end, *retval;	int len, seq = 0;	int error = 0; 	if (buflen < 2)		goto Elong; 	rcu_read_lock();restart:	dentry = d;	end = buf + buflen;	len = buflen;	prepend(&end, &len, "\0", 1);	/* Get '/' right */	retval = end-1;	*retval = '/';	read_seqbegin_or_lock(&rename_lock, &seq);	while (!IS_ROOT(dentry)) {		struct dentry *parent = dentry->d_parent; 		prefetch(parent);		error = prepend_name(&end, &len, &dentry->d_name);		if (error)			break; 		retval = end;		dentry = parent;	}	if (!(seq & 1))		rcu_read_unlock();	if (need_seqretry(&rename_lock, seq)) {		seq = 1;		goto restart;	}	done_seqretry(&rename_lock, seq);	if (error)		goto Elong;	return retval;Elong:	return ERR_PTR(-ENAMETOOLONG);} char *dentry_path_raw(struct dentry *dentry, char *buf, int buflen){	return __dentry_path(dentry, buf, buflen);}EXPORT_SYMBOL(dentry_path_raw); char *dentry_path(struct dentry *dentry, char *buf, int buflen){	char *p = NULL;	char *retval; 	if (d_unlinked(dentry)) {		p = buf + buflen;		if (prepend(&p, &buflen, "//deleted", 10) != 0)			goto Elong;		buflen++;	}	retval = __dentry_path(dentry, buf, buflen);	if (!IS_ERR(retval) && p)		*p = '/';	/* restore '/' overriden with '\0' */	return retval;Elong:	return ERR_PTR(-ENAMETOOLONG);} static void get_fs_root_and_pwd_rcu(struct fs_struct *fs, struct path *root,				    struct path *pwd){	unsigned seq; 	do {		seq = read_seqcount_begin(&fs->seq);		*root = fs->root;		*pwd = fs->pwd;	} while (read_seqcount_retry(&fs->seq, seq));} /* * NOTE! The user-level library version returns a * character pointer. The kernel system call just * returns the length of the buffer filled (which * includes the ending '\0' character), or a negative * error value. So libc would do something like * *	char *getcwd(char * buf, size_t size) *	{ *		int retval; * *		retval = sys_getcwd(buf, size); *		if (retval >= 0) *			return buf; *		errno = -retval; *		return NULL; *	} */SYSCALL_DEFINE2(getcwd, char __user *, buf, unsigned long, size){	int error;	struct path pwd, root;	char *page = __getname(); 	if (!page)		return -ENOMEM; 	rcu_read_lock();	get_fs_root_and_pwd_rcu(current->fs, &root, &pwd); 	error = -ENOENT;	if (!d_unlinked(pwd.dentry)) {		unsigned long len;		char *cwd = page + PATH_MAX;		int buflen = PATH_MAX; 		prepend(&cwd, &buflen, "\0", 1);		error = prepend_path(&pwd, &root, &cwd, &buflen);		rcu_read_unlock(); 		if (error < 0)			goto out; 		/* Unreachable from current root */		if (error > 0) {			error = prepend_unreachable(&cwd, &buflen);			if (error)				goto out;		} 		error = -ERANGE;		len = PATH_MAX + page - cwd;		if (len <= size) {			error = len;			if (copy_to_user(buf, cwd, len))				error = -EFAULT;		}	} else {		rcu_read_unlock();	} out:	__putname(page);	return error;}