[ovs-dev] [PATCH] nx-match: Correct writing of value and length in set_field_to_ofast()

[Simon Horman]

ofpbuf_put_* may reallocate the underlying buffer of the ofpbuf and
thus writing data after a ofpbuf_put_* call must write to memory
relative to the pointer returned by the call.

Prior to this change the length and trailing value would not be written to
the set_field action if ofpbuf_put_* may reallocated the underlying buffer.

Also make use of ofpbuf_put_zero() to avoid calling memset() directly.

Signed-off-by: Simon Horman <horms at verge.net.au>
---
 lib/nx-match.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/lib/nx-match.c b/lib/nx-match.c
index 4ff516e..090c32e 100644
--- a/lib/nx-match.c
+++ b/lib/nx-match.c
@@ -1219,6 +1219,7 @@ set_field_to_ofast(const struct ofpact_reg_load *load,
     const struct mf_field *mf = load->dst.field;
     struct ofp12_action_set_field *oasf;
     uint16_t padded_value_len;
+    char *value;
 
     oasf = ofputil_put_OFPAT12_SET_FIELD(openflow);
     oasf->dst = htonl(mf->oxm_header);
@@ -1226,12 +1227,12 @@ set_field_to_ofast(const struct ofpact_reg_load *load,
     /* Set field is the only action of variable length (so far),
      * so handling the variable length portion is open-coded here */
     padded_value_len = ROUND_UP(mf->n_bytes, 8);
-    ofpbuf_put_uninit(openflow, padded_value_len);
+    value = ofpbuf_put_zeros(openflow, padded_value_len);
+    oasf = (struct ofp12_action_set_field *)value - 1;
     oasf->len = htons(ntohs(oasf->len) + padded_value_len);
-    memset(oasf + 1, 0, padded_value_len);
 
     bitwise_copy(&load->subvalue, sizeof load->subvalue, load->dst.ofs,
-                 oasf + 1, mf->n_bytes, load->dst.ofs, load->dst.n_bits);
+                 value, mf->n_bytes, load->dst.ofs, load->dst.n_bits);
     return;
 }
 
-- 
1.7.10.4