Commit 522f6e6c authored May 23, 2020 by Amir Goldstein Committed by Miklos Szeredi Jun 02, 2020

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



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: cbe7fba8 ("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>

parent 144da23b

fs/overlayfs/overlayfs.h

+3 −0

Original line number	Diff line number	Diff line
		@@ -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);
		}

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