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From df9e0d358ef86e3342525dcdefcf79dc2d749a30 Mon Sep 17 00:00:00 2001
From: Timo Sirainen <timo.sirainen@open-xchange.com>
Date: Thu, 23 Apr 2020 16:59:40 +0300
Subject: [PATCH 10/13] lib-mail: message-parser - Support limiting max number
of nested MIME parts
The default is to allow 100 nested MIME parts. When the limit is reached,
the innermost MIME part's body contains all the rest of the inner bodies
until a parent MIME part is reached.
---
src/lib-mail/message-parser.c | 43 +++++++++++++++++++++++++++++++-------
src/lib-mail/test-message-parser.c | 31 +++++++++++++++++++++++++++
2 files changed, 67 insertions(+), 7 deletions(-)
Signed-off-by: Sana Kazi <Sana.Kazi@kpit.com>
CVE: CVE-2020-12100
Upstream-Status: Backport [http://archive.ubuntu.com/ubuntu/pool/main/d/dovecot/dovecot_2.2.33.2-1ubuntu4.7.debian.tar.xz]
Comment: No change in any hunk
diff --git a/src/lib-mail/message-parser.c b/src/lib-mail/message-parser.c
index 8970d8e0e..721615f76 100644
--- a/src/lib-mail/message-parser.c
+++ b/src/lib-mail/message-parser.c
@@ -13,6 +13,8 @@
#define BOUNDARY_STRING_MAX_LEN (70 + 10)
#define BOUNDARY_END_MAX_LEN (BOUNDARY_STRING_MAX_LEN + 2 + 2)
+#define MESSAGE_PARSER_DEFAULT_MAX_NESTED_MIME_PARTS 100
+
struct message_boundary {
struct message_boundary *next;
@@ -28,9 +30,11 @@ struct message_parser_ctx {
struct istream *input;
struct message_part *parts, *part;
const char *broken_reason;
+ unsigned int nested_parts_count;
enum message_header_parser_flags hdr_flags;
enum message_parser_flags flags;
+ unsigned int max_nested_mime_parts;
char *last_boundary;
struct message_boundary *boundaries;
@@ -206,6 +210,8 @@ message_part_append(struct message_parser_ctx *ctx)
ctx->next_part = &part->children;
ctx->part = part;
+ ctx->nested_parts_count++;
+ i_assert(ctx->nested_parts_count < ctx->max_nested_mime_parts);
}
static void message_part_finish(struct message_parser_ctx *ctx)
@@ -213,8 +219,12 @@ static void message_part_finish(struct message_parser_ctx *ctx)
struct message_part **const *parent_next_partp;
unsigned int count = array_count(&ctx->next_part_stack);
+ i_assert(ctx->nested_parts_count > 0);
+ ctx->nested_parts_count--;
+
parent_next_partp = array_idx(&ctx->next_part_stack, count-1);
array_delete(&ctx->next_part_stack, count-1, 1);
+
ctx->next_part = *parent_next_partp;
message_size_add(&ctx->part->parent->body_size, &ctx->part->body_size);
@@ -592,6 +602,11 @@ static bool block_is_at_eoh(const struct message_block *block)
return FALSE;
}
+static bool parse_too_many_nested_mime_parts(struct message_parser_ctx *ctx)
+{
+ return ctx->nested_parts_count > ctx->max_nested_mime_parts;
+}
+
#define MUTEX_FLAGS \
(MESSAGE_PART_FLAG_MESSAGE_RFC822 | MESSAGE_PART_FLAG_MULTIPART)
@@ -616,8 +631,12 @@ static int parse_next_header(struct message_parser_ctx *ctx,
"\n--boundary" belongs to us or to a previous boundary.
this is a problem if the boundary prefixes are identical,
because MIME requires only the prefix to match. */
- parse_next_body_multipart_init(ctx);
- ctx->multipart = TRUE;
+ if (!parse_too_many_nested_mime_parts(ctx)) {
+ parse_next_body_multipart_init(ctx);
+ ctx->multipart = TRUE;
+ } else {
+ part->flags &= ~MESSAGE_PART_FLAG_MULTIPART;
+ }
}
/* before parsing the header see if we can find a --boundary from here.
@@ -721,12 +740,16 @@ static int parse_next_header(struct message_parser_ctx *ctx,
i_assert(ctx->last_boundary == NULL);
ctx->multipart = FALSE;
ctx->parse_next_block = parse_next_body_to_boundary;
- } else if (part->flags & MESSAGE_PART_FLAG_MESSAGE_RFC822)
+ } else if ((part->flags & MESSAGE_PART_FLAG_MESSAGE_RFC822) != 0 &&
+ !parse_too_many_nested_mime_parts(ctx)) {
ctx->parse_next_block = parse_next_body_message_rfc822_init;
- else if (ctx->boundaries != NULL)
- ctx->parse_next_block = parse_next_body_to_boundary;
- else
- ctx->parse_next_block = parse_next_body_to_eof;
+ } else {
+ part->flags &= ~MESSAGE_PART_FLAG_MESSAGE_RFC822;
+ if (ctx->boundaries != NULL)
+ ctx->parse_next_block = parse_next_body_to_boundary;
+ else
+ ctx->parse_next_block = parse_next_body_to_eof;
+ }
ctx->want_count = 1;
@@ -1100,6 +1123,8 @@ message_parser_init_int(struct istream *input,
ctx = i_new(struct message_parser_ctx, 1);
ctx->hdr_flags = hdr_flags;
ctx->flags = flags;
+ ctx->max_nested_mime_parts =
+ MESSAGE_PARSER_DEFAULT_MAX_NESTED_MIME_PARTS;
ctx->input = input;
i_stream_ref(input);
return ctx;
@@ -1159,6 +1184,10 @@ int message_parser_deinit_from_parts(struct message_parser_ctx **_ctx,
if (ctx->hdr_parser_ctx != NULL)
message_parse_header_deinit(&ctx->hdr_parser_ctx);
boundary_remove_until(ctx, NULL);
+ /* caller might have stopped the parsing early */
+ i_assert(ctx->nested_parts_count == 0 ||
+ i_stream_have_bytes_left(ctx->input));
+
i_stream_unref(&ctx->input);
if (array_is_created(&ctx->next_part_stack))
array_free(&ctx->next_part_stack);
diff --git a/src/lib-mail/test-message-parser.c b/src/lib-mail/test-message-parser.c
index 94aa3eb7c..481d05942 100644
--- a/src/lib-mail/test-message-parser.c
+++ b/src/lib-mail/test-message-parser.c
@@ -166,6 +166,36 @@ static void test_message_parser_small_blocks(void)
test_end();
}
+static void test_message_parser_stop_early(void)
+{
+ struct message_parser_ctx *parser;
+ struct istream *input;
+ struct message_part *parts;
+ struct message_block block;
+ unsigned int i;
+ pool_t pool;
+ int ret;
+
+ test_begin("message parser stop early");
+ pool = pool_alloconly_create("message parser", 10240);
+ input = test_istream_create(test_msg);
+
+ test_istream_set_allow_eof(input, FALSE);
+ for (i = 1; i <= TEST_MSG_LEN+1; i++) {
+ i_stream_seek(input, 0);
+ test_istream_set_size(input, i);
+ parser = message_parser_init(pool, input, 0, 0);
+ while ((ret = message_parser_parse_next_block(parser,
+ &block)) > 0) ;
+ test_assert(ret == 0);
+ message_parser_deinit(&parser, &parts);
+ }
+
+ i_stream_unref(&input);
+ pool_unref(&pool);
+ test_end();
+}
+
static void test_message_parser_truncated_mime_headers(void)
{
static const char input_msg[] =
@@ -740,6 +770,7 @@ int main(void)
{
static void (*test_functions[])(void) = {
test_message_parser_small_blocks,
+ test_message_parser_stop_early,
test_message_parser_truncated_mime_headers,
test_message_parser_truncated_mime_headers2,
test_message_parser_truncated_mime_headers3,
--
2.11.0
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