From 67ea5bea7f84a9a58e05a4f28d787ff3322a3029 Mon Sep 17 00:00:00 2001
From: Oswald Buddenhagen <ossi@users.sf.net>
Date: Mon, 11 Nov 2019 17:24:38 +0100
Subject: [PATCH] handle bogus IMAP FETCH responses more robustly

don't use assert()s when the error condition can stem not only from
errors in mbsync's logic, but also from the IMAP stream being corrupted.

amends 72be55b0e.

REFMAIL: 20191021233411.55ctuvslkfqf2pna@koblih.localdomain
---
 src/drv_imap.c | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/src/drv_imap.c b/src/drv_imap.c
index 4d3a038..48bf6ec 100644
--- a/src/drv_imap.c
+++ b/src/drv_imap.c
@@ -974,7 +974,7 @@ parse_fetch_rsp( imap_store_t *ctx, list_t *list, char *s ATTR_UNUSED )
 	msg_data_t *msgdata;
 	imap_cmd_t *cmdp;
 	uchar mask = 0, status = 0;
-	uint i, uid = 0, size = 0;
+	uint i, uid = 0, need_uid = 0, size = 0;
 	time_t date = 0;
 
 	if (!is_list( list )) {
@@ -990,6 +990,7 @@ parse_fetch_rsp( imap_store_t *ctx, list_t *list, char *s ATTR_UNUSED )
 					error( "IMAP error: unable to parse UID\n" );
 					goto ffail;
 				}
+				continue;  // This *is* the UID.
 			} else if (!strcmp( "FLAGS", tmp->val )) {
 				tmp = tmp->next;
 				if (is_list( tmp )) {
@@ -1018,6 +1019,7 @@ parse_fetch_rsp( imap_store_t *ctx, list_t *list, char *s ATTR_UNUSED )
 						}
 					}
 					status |= M_FLAGS;
+					continue;  // This may legitimately come without UID.
 				} else {
 					error( "IMAP error: unable to parse FLAGS\n" );
 					goto ffail;
@@ -1099,17 +1101,27 @@ parse_fetch_rsp( imap_store_t *ctx, list_t *list, char *s ATTR_UNUSED )
 				}
 			}
 		}
+		need_uid = 1;
 	}
 
 	if (!uid) {
-		assert( !body && !tuid && !msgid );
+		if (need_uid) {
+			error( "IMAP error: received payload without UID\n" );
+			goto ffail;
+		}
 		// Ignore async flag updates for now.
 	} else if ((cmdp = ctx->in_progress) && cmdp->param.lastuid) {
-		assert( !body && !tuid && !msgid );
+		if (need_uid || (status & M_FLAGS)) {
+			error( "IMAP error: received extraneous data in response to UID query\n" );
+			goto ffail;
+		}
 		// Workaround for server not sending UIDNEXT and/or APPENDUID.
 		ctx->uidnext = uid + 1;
 	} else if (body) {
-		assert( !tuid && !msgid );
+		if (tuid || msgid) {  // Only those that leak; ignore others.
+			error( "IMAP error: received extraneous data with full message\n" );
+			goto ffail;
+		}
 		for (cmdp = ctx->in_progress; cmdp; cmdp = cmdp->next)
 			if (cmdp->param.uid == uid)
 				goto gotuid;