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

commit cf8aa9bf97cadf85745506c6a3e244b22c268d63 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/overlayfs/export.c b/fs/overlayfs/export.c
index e065a5b9a442e2007cdf8623154eeb9d6f772ab5..ac9c3ad04016ed2c3c4d7c8b63911ccf822b7e58 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 eee8f08d32b639b1fe69fe28fae89353d060666e..e74a610a117ec14969ece9b3cb23684ab3e1f4cb 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;