evaluate: honor statement length in bitwise evaluation

Get length from statement, instead infering it from the expression that
is used to set the value. In the particular case of {ct|meta} mark, this
is 32 bits.

Otherwise, bytecode generation is not correct:

 # nft -c --debug=netlink 'add rule ip6 x y ct mark set ip6 dscp << 2 | 0x10'
  [ payload load 2b @ network header + 0 => reg 1 ]
  [ bitwise reg 1 = ( reg 1 & 0x0000c00f ) ^ 0x00000000 ]
  [ bitwise reg 1 = ( reg 1 >> 0x00000006 ) ]
  [ byteorder reg 1 = ntoh(reg 1, 2, 1) ]
  [ bitwise reg 1 = ( reg 1 << 0x00000002 ) ]
  [ bitwise reg 1 = ( reg 1 & 0x00000fef ) ^ 0x00000010 ]    <--- incorrect!
  [ ct set mark with reg 1 ]

the previous bitwise shift already upgraded to 32-bits (not visible from
the netlink debug output above).

After this patch, the last | 0x10 uses 32-bits:

 [ bitwise reg 1 = ( reg 1 & 0xffffffef ) ^ 0x00000010 ]

note that mask 0xffffffef is used instead of 0x00000fef.

Patch ("evaluate: support shifts larger than the width of the left operand")
provides the statement length through eval context. Use it to evaluate the
bitwise expression accordingly, otherwise bytecode is incorrect:

 # nft --debug=netlink add rule ip x y 'ct mark set ip dscp & 0x0f << 1 | 0xff000000'
 ip x y
  [ payload load 1b @ network header + 1 => reg 1 ]
  [ bitwise reg 1 = ( reg 1 & 0x000000fc ) ^ 0x00000000 ]
  [ bitwise reg 1 = ( reg 1 >> 0x00000002 ) ]
  [ bitwise reg 1 = ( reg 1 & 0x1e000000 ) ^ 0x000000ff ]  <-- incorrect byteorder for OR
  [ byteorder reg 1 = ntoh(reg 1, 4, 4) ]		   <-- no needed for single ip dscp byte
  [ ct set mark with reg 1 ]

Correct bytecode:

 # nft --debug=netlink add rule ip x y 'ct mark set ip dscp & 0x0f << 1 | 0xff000000
 ip x y
  [ payload load 1b @ network header + 1 => reg 1 ]
  [ bitwise reg 1 = ( reg 1 & 0x000000fc ) ^ 0x00000000 ]
  [ bitwise reg 1 = ( reg 1 >> 0x00000002 ) ]
  [ bitwise reg 1 = ( reg 1 & 0x0000001e ) ^ 0xff000000 ]
  [ ct set mark with reg 1 ]

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

0 files changed, 0 insertions, 0 deletions