Commit e896474f authored by Al Viro's avatar Al Viro
Browse files

getname_maybe_null() - the third variant of pathname copy-in 



Semantics used by statx(2) (and later *xattrat(2)): without AT_EMPTY_PATH
it's standard getname() (i.e. ERR_PTR(-ENOENT) on empty string,
ERR_PTR(-EFAULT) on NULL), with AT_EMPTY_PATH both empty string and
NULL are accepted.

Calling conventions: getname_maybe_null(user_pointer, flags) returns
	* pointer to struct filename when non-empty string had been
successfully read
	* ERR_PTR(...) on error
	* NULL if an empty string or NULL pointer had been given
with AT_EMPTY_PATH in the flags argument.

It tries to avoid allocation in the last case; it's not always
able to do so, in which case the temporary struct filename instance
is freed and NULL returned anyway.

Fast path is inlined.

Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 5b313bcb

fs/namei.c

+23 −7
Original line number Diff line number Diff line
@@ -211,22 +211,38 @@ getname_flags(const char __user *filename, int flags) 
	return result;

}



struct filename *

getname_uflags(const char __user *filename, int uflags)

struct filename *getname_uflags(const char __user *filename, int uflags)

{

	int flags = (uflags & AT_EMPTY_PATH) ? LOOKUP_EMPTY : 0;



	return getname_flags(filename, flags);

}



struct filename *

getname(const char __user * filename)

struct filename *getname(const char __user * filename)

{

	return getname_flags(filename, 0);

}



struct filename *

getname_kernel(const char * filename)

struct filename *__getname_maybe_null(const char __user *pathname)

{

	struct filename *name;

	char c;



	/* try to save on allocations; loss on um, though */

	if (get_user(c, pathname))

		return ERR_PTR(-EFAULT);

	if (!c)

		return NULL;



	name = getname_flags(pathname, LOOKUP_EMPTY);

	if (!IS_ERR(name) && !(name->name[0])) {

		putname(name);

		name = NULL;

	}

	return name;

}



struct filename *getname_kernel(const char * filename)

{

	struct filename *result;

	int len = strlen(filename) + 1;
@@ -264,7 +280,7 @@ EXPORT_SYMBOL(getname_kernel); 


void putname(struct filename *name)

{

	if (IS_ERR(name))

	if (IS_ERR_OR_NULL(name))

		return;



	if (WARN_ON_ONCE(!atomic_read(&name->refcnt)))

fs/stat.c

+4 −24
Original line number Diff line number Diff line
@@ -326,18 +326,11 @@ int vfs_fstatat(int dfd, const char __user *filename, 
{

	int ret;

	int statx_flags = flags | AT_NO_AUTOMOUNT;

	struct filename *name;

	struct filename *name = getname_maybe_null(filename, flags);



	/*

	 * Work around glibc turning fstat() into fstatat(AT_EMPTY_PATH)

	 *

	 * If AT_EMPTY_PATH is set, we expect the common case to be that

	 * empty path, and avoid doing all the extra pathname work.

	 */

	if (flags == AT_EMPTY_PATH && vfs_empty_path(dfd, filename))

	if (!name && dfd >= 0)

		return vfs_fstat(dfd, stat);



	name = getname_flags(filename, getname_statx_lookup_flags(statx_flags));

	ret = vfs_statx(dfd, name, statx_flags, stat, STATX_BASIC_STATS);

	putname(name);
@@ -774,24 +767,11 @@ SYSCALL_DEFINE5(statx, 
		struct statx __user *, buffer)

{

	int ret;

	unsigned lflags;

	struct filename *name;

	struct filename *name = getname_maybe_null(filename, flags);



	/*

	 * Short-circuit handling of NULL and "" paths.

	 *

	 * For a NULL path we require and accept only the AT_EMPTY_PATH flag

	 * (possibly |'d with AT_STATX flags).

	 *

	 * However, glibc on 32-bit architectures implements fstatat as statx

	 * with the "" pathname and AT_NO_AUTOMOUNT | AT_EMPTY_PATH flags.

	 * Supporting this results in the uglification below.

	 */

	lflags = flags & ~(AT_NO_AUTOMOUNT | AT_STATX_SYNC_TYPE);

	if (lflags == AT_EMPTY_PATH && vfs_empty_path(dfd, filename))

	if (!name && dfd >= 0)

		return do_statx_fd(dfd, flags & ~AT_NO_AUTOMOUNT, mask, buffer);



	name = getname_flags(filename, getname_statx_lookup_flags(flags));

	ret = do_statx(dfd, name, flags, mask, buffer);

	putname(name);

include/linux/fs.h

+10 −0
Original line number Diff line number Diff line
@@ -2766,6 +2766,16 @@ extern struct filename *getname_flags(const char __user *, int); 
extern struct filename *getname_uflags(const char __user *, int);

extern struct filename *getname(const char __user *);

extern struct filename *getname_kernel(const char *);

extern struct filename *__getname_maybe_null(const char __user *);

static inline struct filename *getname_maybe_null(const char __user *name, int flags)

{

	if (!(flags & AT_EMPTY_PATH))

		return getname(name);



	if (!name)

		return NULL;

	return __getname_maybe_null(name);

}

extern void putname(struct filename *name);



extern int finish_open(struct file *file, struct dentry *dentry,