From: Christopher Faulet <cfaulet@haproxy.com>
Date: Mon, 28 Feb 2022 14:29:56 +0000 (+0100)
Subject: BUG/MEDIUM: htx: Fix a possible null derefs in htx_xfer_blks()
X-Git-Tag: v2.6-dev3~106
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=234a10aa9bce34781b5b0b4c4ffb595e7563eb41;p=thirdparty%2Fhaproxy.git

BUG/MEDIUM: htx: Fix a possible null derefs in htx_xfer_blks()

In htx_xfer_blks() function, when headers or trailers are partially
transferred, we rollback the copy by removing copied blocks. Internally, all
blocks between <dstref> and <dstblk> are removed. But if the transfer was
stopped because we failed to reserve a block, the variable <dstblk> is
NULL. Thus, we must not try to remove it. It is unexpected to call
htx_remove_blk() in this case.

htx_remove_blk() was updated to test <blk> variable inside the existing
BUG_ON(). The block must be defined.

For now, this bug may only be encountered when H2 trailers are copied. On H2
headers, the destination buffer is empty. Thus a swap is performed.

This patch should fix the issue #1578. It must be backported as far as 2.4.
---

diff --git a/src/htx.c b/src/htx.c
index 3cc1a34b05..7e5bd46186 100644
--- a/src/htx.c
+++ b/src/htx.c
@@ -336,7 +336,7 @@ struct htx_blk *htx_remove_blk(struct htx *htx, struct htx_blk *blk)
 	enum htx_blk_type type;
 	uint32_t pos, addr, sz;
 
-	BUG_ON(htx->head == -1);
+	BUG_ON(!blk || htx->head == -1);
 
 	/* This is the last block in use */
 	if (htx->head == htx->tail) {
@@ -739,12 +739,14 @@ struct htx_ret htx_xfer_blks(struct htx *dst, struct htx *src, uint32_t count,
 	}
 
 	if (unlikely(dstref)) {
-		/* Headers or trailers part was partially xferred, so rollback the copy
-		 * by removing all block between <dstref> and <dstblk>, both included.
+		/* Headers or trailers part was partially xferred, so rollback
+		 * the copy by removing all block between <dstref> and <dstblk>,
+		 * both included. <dstblk> may be NULL.
 		 */
 		while (dstref && dstref != dstblk)
 			dstref = htx_remove_blk(dst, dstref);
-		htx_remove_blk(dst, dstblk);
+		if (dstblk)
+			htx_remove_blk(dst, dstblk);
 
 		/* <dst> HTX message is empty, it means the headers or trailers
 		 * part is too big to be copied at once.