From e896474fe4851ffc4dd860c92daa906783090346 Mon Sep 17 00:00:00 2001 From: Al Viro Date: Mon, 7 Oct 2024 23:08:34 -0400 Subject: [PATCH] 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 --- fs/namei.c | 30 +++++++++++++++++++++++------- fs/stat.c | 28 ++++------------------------ include/linux/fs.h | 10 ++++++++++ 3 files changed, 37 insertions(+), 31 deletions(-) diff --git a/fs/namei.c b/fs/namei.c index aaf3cd6c802f..2bfe476c3bd0 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -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))) diff --git a/fs/stat.c b/fs/stat.c index 41e598376d7e..b74831dc7ae6 100644 --- a/fs/stat.c +++ b/fs/stat.c @@ -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); diff --git a/include/linux/fs.h b/include/linux/fs.h index e3c603d01337..403258ac2ea2 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -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,