On 11/8/22 19:15, Simon Horman wrote:
> On Sat, Nov 05, 2022 at 11:11:53AM +0100, Ilya Maximets wrote:
>> The value is right-justified after the string parsing with
>> parse_int_string(), i.e. it is in BE byte order and aligned
>> to the right side of the array.
>>
>> For example, the 0x10011 value in a 4-byte field will look
>> like 0x00 0x01 0x00 0x11.
>>
>> However, value copy to the resulted ofpact is performed
>> from the start of the memory. So, in case the destination
>> size is smaller than the original field size, incorrect
>> part of the value will be copied.
>>
>> In the 0x00 0x01 0x00 0x11 example above, if the copy is
>> performed to a 3-byte field, the first 3 bytes will be
>> copied, which are 0x00 0x01 0x00 instead of 0x01 0x00 0x11.
>>
>> This leads to a problem where NXM_NX_REG3[0..16]=0x10011
>> turns into NXM_NX_REG3[0..16]=0x100 after the parsing.
>>
>> Fix that by offsetting the starting position to the size
>> difference in bytes similarly to how it is done in
>> learn_parse_load_immediate().
>>
>> Fixes: 21b2fa617126 ("ofp-parse: Allow match field names in actions and
>> brackets in matches.")
>> Reported-at:
>> https://mail.openvswitch.org/pipermail/ovs-discuss/2022-November/052100.html
>> Reported-by: Thomas Lee <newsfortho...@engineer.com>
>> Signed-off-by: Ilya Maximets <i.maxim...@ovn.org>
>> ---
>> lib/learn.c | 4 +++-
>> tests/learn.at | 4 ++--
>> 2 files changed, 5 insertions(+), 3 deletions(-)
>>
>> diff --git a/lib/learn.c b/lib/learn.c
>> index a40209ec0..cfd762527 100644
>> --- a/lib/learn.c
>> +++ b/lib/learn.c
>> @@ -310,9 +310,11 @@ learn_parse_spec(const char *orig, char *name, char
>> *value,
>>
>> /* Push value last, as this may reallocate 'spec'! */
>> unsigned int imm_bytes = DIV_ROUND_UP(dst.n_bits, 8);
>> + unsigned int offset = dst.field->n_bytes - imm_bytes;
>> uint8_t *src_imm = ofpbuf_put_zeros(ofpacts,
>>
>> OFPACT_ALIGN(imm_bytes));
>> - memcpy(src_imm, &imm, imm_bytes);
>> +
>> + memcpy(src_imm, (uint8_t *) &imm + offset, imm_bytes);
>
> FWIIW, This seems fine to me, but I wonder if
> it would nicer (and indeed valid) to use &imm.u8 here.
I guess, you meant 'imm.b', since we have mf_value and not mf_subvalue
here. But I agree that it makes more sense. Thanks! I'll also change
other places where &imm is used as a pointer to a byte array to make
the code a bit more clear. Will send v2 shortly.
Sorry for the late reply, just got back from my PTO.
Best regards, Ilya Maximets.
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