linux-kernel - [PATCH 5.6 115/161] ovl: fix out of bounds access warning in ovl_check_fb

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Message-Id: <20200616153111.834564988@linuxfoundation.org>
Date:   Tue, 16 Jun 2020 17:35:05 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Amir Goldstein <amir73il@...il.com>,
        Miklos Szeredi <mszeredi@...hat.com>,
        syzbot+61958888b1c60361a791@...kaller.appspotmail.com
Subject: [PATCH 5.6 115/161] ovl: fix out of bounds access warning in ovl_check_fb_len()

From: Amir Goldstein <amir73il@...il.com>

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@...kaller.appspotmail.com
Cc: <stable@...r.kernel.org> # v5.5
Signed-off-by: Amir Goldstein <amir73il@...il.com>
Signed-off-by: Miklos Szeredi <mszeredi@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/overlayfs/overlayfs.h |    3 +++
 1 file changed, 3 insertions(+)

--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -339,6 +339,9 @@ int ovl_check_fb_len(struct ovl_fb *fb,
 
 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);
 }