From: Willy Tarreau <w@1wt.eu>
Date: Thu, 21 Oct 2021 13:05:34 +0000 (+0200)
Subject: BUG/MAJOR: buf: fix varint API post- vs pre- increment
X-Git-Tag: v2.5-dev11~18
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=dd362b7b24ea24d8f3c882dab1a69cf78af7cc90;p=thirdparty%2Fhaproxy.git

BUG/MAJOR: buf: fix varint API post- vs pre- increment

A bogus test in b_get_varint(), b_put_varint(), b_peek_varint() shifts
the end of the buffer by one byte. Since the bug is the same in the read
and write functions, the buffer contents remain compatible, which explains
why this bug was not detected earlier. But if the buffer ends on an
aligned address or page, it can result in a one-byte overflow which will
typically cause a crash or an inconsistent behavior.

This API is only used by rings (e.g. for traces and boot messages) and
by DNS responses, so the probability to hit it is extremely low, but a
crash on boot was observed.

This must be backported to 2.2.
---

diff --git a/include/haproxy/buf.h b/include/haproxy/buf.h
index 20f260d195..78409c028f 100644
--- a/include/haproxy/buf.h
+++ b/include/haproxy/buf.h
@@ -763,7 +763,7 @@ static inline void __b_put_varint(struct buffer *b, uint64_t v)
 		v = (v - 0xF0) >> 4;
 
 		while (1) {
-			if (tail++ == wrap)
+			if (++tail == wrap)
 				tail -= size;
 			data++;
 			if (v < 0x80)
@@ -798,7 +798,7 @@ static inline int b_put_varint(struct buffer *b, uint64_t v)
 		v = (v - 0xF0) >> 4;
 
 		while (1) {
-			if (tail++ == wrap)
+			if (++tail == wrap)
 				tail -= size;
 			data++;
 			if (data == size || v < 0x80)
@@ -837,7 +837,7 @@ static inline int b_get_varint(struct buffer *b, uint64_t *vptr)
 		v = *head;
 		bits += 4;
 		while (1) {
-			if (head++ == wrap)
+			if (++head == wrap)
 				head -= size;
 			data--;
 			if (!data || !(*head & 0x80))
@@ -879,7 +879,7 @@ static inline int b_peek_varint(struct buffer *b, size_t ofs, uint64_t *vptr)
 		v = *head;
 		bits += 4;
 		while (1) {
-			if (head++ == wrap)
+			if (++head == wrap)
 				head -= size;
 			data--;
 			if (!data || !(*head & 0x80))