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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: Al Viro <viro@zeniv.linux.org.uk>
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parent
5b313bcb6e
commit
e896474fe4
30
fs/namei.c
30
fs/namei.c
@ -211,22 +211,38 @@ getname_flags(const char __user *filename, int flags)
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return result;
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}
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struct filename *
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getname_uflags(const char __user *filename, int uflags)
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struct filename *getname_uflags(const char __user *filename, int uflags)
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{
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int flags = (uflags & AT_EMPTY_PATH) ? LOOKUP_EMPTY : 0;
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return getname_flags(filename, flags);
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}
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struct filename *
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getname(const char __user * filename)
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struct filename *getname(const char __user * filename)
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{
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return getname_flags(filename, 0);
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}
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struct filename *
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getname_kernel(const char * filename)
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struct filename *__getname_maybe_null(const char __user *pathname)
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{
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struct filename *name;
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char c;
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/* try to save on allocations; loss on um, though */
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if (get_user(c, pathname))
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return ERR_PTR(-EFAULT);
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if (!c)
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return NULL;
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name = getname_flags(pathname, LOOKUP_EMPTY);
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if (!IS_ERR(name) && !(name->name[0])) {
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putname(name);
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name = NULL;
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}
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return name;
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}
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struct filename *getname_kernel(const char * filename)
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{
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struct filename *result;
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int len = strlen(filename) + 1;
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@ -264,7 +280,7 @@ EXPORT_SYMBOL(getname_kernel);
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void putname(struct filename *name)
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{
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if (IS_ERR(name))
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if (IS_ERR_OR_NULL(name))
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return;
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if (WARN_ON_ONCE(!atomic_read(&name->refcnt)))
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28
fs/stat.c
28
fs/stat.c
@ -326,18 +326,11 @@ int vfs_fstatat(int dfd, const char __user *filename,
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{
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int ret;
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int statx_flags = flags | AT_NO_AUTOMOUNT;
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struct filename *name;
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struct filename *name = getname_maybe_null(filename, flags);
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/*
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* Work around glibc turning fstat() into fstatat(AT_EMPTY_PATH)
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*
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* If AT_EMPTY_PATH is set, we expect the common case to be that
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* empty path, and avoid doing all the extra pathname work.
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*/
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if (flags == AT_EMPTY_PATH && vfs_empty_path(dfd, filename))
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if (!name && dfd >= 0)
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return vfs_fstat(dfd, stat);
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name = getname_flags(filename, getname_statx_lookup_flags(statx_flags));
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ret = vfs_statx(dfd, name, statx_flags, stat, STATX_BASIC_STATS);
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putname(name);
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@ -774,24 +767,11 @@ SYSCALL_DEFINE5(statx,
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struct statx __user *, buffer)
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{
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int ret;
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unsigned lflags;
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struct filename *name;
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struct filename *name = getname_maybe_null(filename, flags);
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/*
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* Short-circuit handling of NULL and "" paths.
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*
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* For a NULL path we require and accept only the AT_EMPTY_PATH flag
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* (possibly |'d with AT_STATX flags).
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*
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* However, glibc on 32-bit architectures implements fstatat as statx
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* with the "" pathname and AT_NO_AUTOMOUNT | AT_EMPTY_PATH flags.
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* Supporting this results in the uglification below.
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*/
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lflags = flags & ~(AT_NO_AUTOMOUNT | AT_STATX_SYNC_TYPE);
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if (lflags == AT_EMPTY_PATH && vfs_empty_path(dfd, filename))
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if (!name && dfd >= 0)
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return do_statx_fd(dfd, flags & ~AT_NO_AUTOMOUNT, mask, buffer);
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name = getname_flags(filename, getname_statx_lookup_flags(flags));
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ret = do_statx(dfd, name, flags, mask, buffer);
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putname(name);
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@ -2766,6 +2766,16 @@ extern struct filename *getname_flags(const char __user *, int);
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extern struct filename *getname_uflags(const char __user *, int);
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extern struct filename *getname(const char __user *);
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extern struct filename *getname_kernel(const char *);
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extern struct filename *__getname_maybe_null(const char __user *);
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static inline struct filename *getname_maybe_null(const char __user *name, int flags)
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{
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if (!(flags & AT_EMPTY_PATH))
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return getname(name);
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if (!name)
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return NULL;
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return __getname_maybe_null(name);
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}
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extern void putname(struct filename *name);
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extern int finish_open(struct file *file, struct dentry *dentry,
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