From: Aurelien DARRAGON <adarragon@haproxy.com>
Date: Tue, 7 Mar 2023 16:45:02 +0000 (+0100)
Subject: BUG/MINOR: dns: fix ring offset calculation on first read
X-Git-Tag: v2.8-dev5~20
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=5a43db2c5d33b9ec575b2faa4eb0921af234824d;p=thirdparty%2Fhaproxy.git

BUG/MINOR: dns: fix ring offset calculation on first read

With 737d10f ("BUG/MEDIUM: dns: ensure ring offset is properly reajusted
to head") ring offset is now properly re-adjusted in dns_session_io_handler()
and dns_process_req().

But the previous patch does not cope well if the first read is performed
on a non-empty ring since relative ofs will be computed from ds->ofs=0 or
dss->ofs_req=0.
In this case: relative offset could become invalid since we mix up relative
offsets with absolute offsets.

To fix this, we apply the same logic performed in d9c7188 ("MEDIUM: ring:
make the offset relative to the head/tail instead of absolute") for the
cli_io_handler_show_ring() function: that is using b_peek_ofs(buf, 0) to
set the contextual offset instead of hard-coding it to 0.

This should be considered as a minor bugfix since this bug was discovered by
reading the code: 737d10f already survived a good amount of stress-tests as
shown in GH #2068.

No backport needed as 737d10f is not marked for backports.
---

diff --git a/src/dns.c b/src/dns.c
index 1e6f287bb5..5d7e1d9401 100644
--- a/src/dns.c
+++ b/src/dns.c
@@ -489,9 +489,8 @@ static void dns_session_io_handler(struct appctx *appctx)
 	 * value cannot be produced after initialization.
 	 */
 	if (unlikely(ds->ofs == ~0)) {
-		ds->ofs = 0;
-
-		HA_ATOMIC_INC(b_peek(buf, ds->ofs));
+		ds->ofs = b_peek_ofs(buf, 0);
+		HA_ATOMIC_INC(b_orig(buf) + ds->ofs);
 	}
 
 	/* in this loop, ofs always points to the counter byte that precedes
@@ -1120,8 +1119,8 @@ static struct task *dns_process_req(struct task *t, void *context, unsigned int
 	 * value cannot be produced after initialization.
 	 */
 	if (unlikely(dss->ofs_req == ~0)) {
-		dss->ofs_req = 0;
-		HA_ATOMIC_INC(b_peek(buf, dss->ofs_req));
+		dss->ofs_req = b_peek_ofs(buf, 0);
+		HA_ATOMIC_INC(b_orig(buf) + dss->ofs_req);
 	}
 
 	/* we were already there, adjust the offset to be relative to