From: Amir Goldstein <amir73il@gmail.com>
Date: Sat, 23 May 2020 13:21:55 +0000 (+0300)
Subject: ovl: fix out of bounds access warning in ovl_check_fb_len()
X-Git-Tag: v5.7.3~50
X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=59c79f3957450ca093f4928415fafa9e463ee030;p=users%2Fdwmw2%2Flinux.git

ovl: fix out of bounds access warning in ovl_check_fb_len()

commit 522f6e6cba6880a038e2bd88e10390b84cd3febd upstream.

syzbot reported out of bounds memory access from open_by_handle_at()
with a crafted file handle that looks like this:

  { .handle_bytes = 2, .handle_type = OVL_FILEID_V1 }

handle_bytes gets rounded down to 0 and we end up calling:
  ovl_check_fh_len(fh, 0) => ovl_check_fb_len(fh + 3, -3)

But fh buffer is only 2 bytes long, so accessing struct ovl_fb at
fh + 3 is illegal.

Fixes: cbe7fba8edfc ("ovl: make sure that real fid is 32bit aligned in memory")
Reported-and-tested-by: syzbot+61958888b1c60361a791@syzkaller.appspotmail.com
Cc: <stable@vger.kernel.org> # v5.5
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index e6f3670146ed1..64039f36c54d0 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -355,6 +355,9 @@ int ovl_check_fb_len(struct ovl_fb *fb, int fb_len);
 
 static inline int ovl_check_fh_len(struct ovl_fh *fh, int fh_len)
 {
+	if (fh_len < sizeof(struct ovl_fh))
+		return -EINVAL;
+
 	return ovl_check_fb_len(&fh->fb, fh_len - OVL_FH_WIRE_OFFSET);
 }