[netsniff-ng] [PATCH v2 1/4] trafgen: proto: Fix bad field masking

[Vadim Kochan]

Current logic does OR of existing field value & shift-masked
specified value, which is not enough as 0s bits from
the specified value will be not set (be cause of OR),
so fixed it by reseting original field value by AND with
reverted field mask, in otherwords - bits part of original field
value is reset to 0s and only after OR-ed with specified shift-masked
value.

Signed-off-by: Vadim Kochan <vadi...@gmail.com>
---
 trafgen_proto.c | 24 ++++++++++++++++++++----
 1 file changed, 20 insertions(+), 4 deletions(-)

diff --git a/trafgen_proto.c b/trafgen_proto.c
index efa8fce..214547e 100644
--- a/trafgen_proto.c
+++ b/trafgen_proto.c
@@ -182,7 +182,9 @@ static void __proto_field_set_bytes(struct proto_hdr *hdr, 
uint32_t fid,
                                    uint8_t *bytes, bool is_default, bool is_be)
 {
        struct proto_field *field;
-       uint8_t *payload;
+       uint8_t *payload, *p8;
+       uint16_t *p16;
+       uint32_t *p32;
        uint32_t v32;
        uint16_t v16;
        uint8_t v8;
@@ -195,18 +197,32 @@ static void __proto_field_set_bytes(struct proto_hdr 
*hdr, uint32_t fid,
        payload = &current_packet()->payload[field->pkt_offset];
 
        if (field->len == 1) {
+               p8 = payload;
+               *p8 = field->mask ? *p8 & ~field->mask : *p8;
+
                v8 = field_shift_and_mask(field, *bytes);
-               v8 = field->mask ? (v8 | *payload) : v8;
+               v8 = field->mask ? (v8 | *p8) : v8;
+
                bytes = &v8;
        } else if (field->len == 2) {
+               p16 = (uint16_t *)payload;
+               *p16 = be16_to_cpu(*p16);
+               *p16 = cpu_to_be16(field->mask ? *p16 & ~field->mask : *p16);
+
                v16 = field_shift_and_mask(field, *(uint16_t *)bytes);
                v16 = is_be ? cpu_to_be16(v16) : v16;
-               v16 = field->mask ? (v16 | *(uint16_t *)payload) : v16;
+               v16 = field->mask ? (v16 | *p16) : v16;
+
                bytes = (uint8_t *)&v16;
        } else if (field->len == 4) {
+               p32 = (uint32_t *)payload;
+               *p32 = be32_to_cpu(*p32);
+               *p32 = cpu_to_be32(field->mask ? *p32 & ~field->mask : *p32);
+
                v32 = field_shift_and_mask(field, *(uint32_t *)bytes);
                v32 = is_be ? cpu_to_be32(v32) : v32;
-               v32 = field->mask ? (v32 | *(uint32_t *)payload) : v32;
+               v32 = field->mask ? (v32 | *p32) : v32;
+
                bytes = (uint8_t *)&v32;
        }
 
-- 
2.6.3

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