Re: [syzbot] [overlayfs?] general protection fault in ovl_llseek

[Leo Stone <leocstone@xxxxxxxxx>]

Add a check to avoid using an invalid pointer if ovl_open_realfile fails.

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
index 2b7a5a3a7a2f..67f75eeb1e51 100644
--- a/fs/overlayfs/file.c
+++ b/fs/overlayfs/file.c
@@ -117,7 +117,11 @@ static int ovl_real_fdget_meta(const struct file *file, struct fd *real,
                struct file *f = ovl_open_realfile(file, &realpath);
                if (IS_ERR(f))
                        return PTR_ERR(f);
-               real->word = (unsigned long)ovl_open_realfile(file, &realpath) | FDPUT_FPUT;
+               f = ovl_open_realfile(file, &realpath);
+               if (IS_ERR(f))
+                       return PTR_ERR(f);
+               real->word = (unsigned long)f;
+               real->word |= FDPUT_FPUT;
                return 0;
        }