kernfs: Convert kernfs_walk_ns() from strlcpy() to strscpy()

strlcpy() reads the entire source buffer first. This read may exceed
the destination size limit. This is both inefficient and can lead
to linear read overflows if a source string is not NUL-terminated[1].
Additionally, it returns the size of the source string, not the
resulting size of the destination string. In an effort to remove strlcpy()
completely[2], replace strlcpy() here with strscpy().

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strlcpy
Link: https://github.com/KSPP/linux/issues/89
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Azeem Shaikh <azeemshaikh38@gmail.com>
Link: https://lore.kernel.org/r/20231116192127.1558276-1-keescook@chromium.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20231212211741.164376-1-keescook@chromium.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index 62d39ecf0a466b62eb7781e7e499ddf8b342fdf3..fa9077576e02808d8f295cedaeab7e8dc3a17c4d 100644 (file)
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -862,16 +862,16 @@ static struct kernfs_node *kernfs_walk_ns(struct kernfs_node *parent,
                                          const unsigned char *path,
                                          const void *ns)
 {
-       size_t len;
+       ssize_t len;
        char *p, *name;
 
        lockdep_assert_held_read(&kernfs_root(parent)->kernfs_rwsem);
 
        spin_lock_irq(&kernfs_pr_cont_lock);
 
-       len = strlcpy(kernfs_pr_cont_buf, path, sizeof(kernfs_pr_cont_buf));
+       len = strscpy(kernfs_pr_cont_buf, path, sizeof(kernfs_pr_cont_buf));
 
-       if (len >= sizeof(kernfs_pr_cont_buf)) {
+       if (len < 0) {
                spin_unlock_irq(&kernfs_pr_cont_lock);
                return NULL;
        }