ovl: Use "buf" flexible array for memcpy() destination

The "buf" flexible array needs to be the memcpy() destination to avoid
false positive run-time warning from the recent FORTIFY_SOURCE
hardening:

  memcpy: detected field-spanning write (size 93) of single field "&fh->fb"
  at fs/overlayfs/export.c:799 (size 21)

Reported-by: syzbot+9d14351a171d0d1c7955@syzkaller.appspotmail.com
Link: https://lore.kernel.org/all/000000000000763a6c05e95a5985@google.com/
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

diff --git a/fs/overlayfs/export.c b/fs/overlayfs/export.c
index e065a5b..ac9c3ad 100644 (file)
--- a/fs/overlayfs/export.c
+++ b/fs/overlayfs/export.c
@@ -796,7 +796,7 @@ static struct ovl_fh *ovl_fid_to_fh(struct fid *fid, int buflen, int fh_type)
                return ERR_PTR(-ENOMEM);
 
        /* Copy unaligned inner fh into aligned buffer */
-       memcpy(&fh->fb, fid, buflen - OVL_FH_WIRE_OFFSET);
+       memcpy(fh->buf, fid, buflen - OVL_FH_WIRE_OFFSET);
        return fh;
 }
 

diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index eee8f08..e74a610 100644 (file)
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -108,7 +108,7 @@ struct ovl_fh {
        u8 padding[3];  /* make sure fb.fid is 32bit aligned */
        union {
                struct ovl_fb fb;
-               u8 buf[0];
+               DECLARE_FLEX_ARRAY(u8, buf);
        };
 } __packed;