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From ee8ea4f1c88a0393206769cd30a545dc3375f868 Mon Sep 17 00:00:00 2001
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From: =?UTF-8?q?Lubo=C5=A1=20Uhliarik?= <luhliari@redhat.com>
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Date: Wed, 2 Feb 2022 20:14:55 +0100
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Subject: [PATCH] Fix ALPACA security issue
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---
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 src/mail/ngx_mail.h             |  3 +++
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 src/mail/ngx_mail_core_module.c | 10 ++++++++++
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 src/mail/ngx_mail_handler.c     | 15 ++++++++++++++-
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 3 files changed, 27 insertions(+), 1 deletion(-)
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diff --git a/src/mail/ngx_mail.h b/src/mail/ngx_mail.h
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index b865a3b..76cae37 100644
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--- a/src/mail/ngx_mail.h
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+++ b/src/mail/ngx_mail.h
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@@ -115,6 +115,8 @@ typedef struct {
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     ngx_msec_t              timeout;
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     ngx_msec_t              resolver_timeout;
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+    ngx_uint_t              max_errors;
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+
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     ngx_str_t               server_name;
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     u_char                 *file_name;
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@@ -231,6 +233,7 @@ typedef struct {
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     ngx_uint_t              command;
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     ngx_array_t             args;
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+    ngx_uint_t              errors;
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     ngx_uint_t              login_attempt;
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     /* used to parse POP3/IMAP/SMTP command */
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diff --git a/src/mail/ngx_mail_core_module.c b/src/mail/ngx_mail_core_module.c
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index 4083124..115671c 100644
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--- a/src/mail/ngx_mail_core_module.c
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+++ b/src/mail/ngx_mail_core_module.c
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@@ -85,6 +85,13 @@ static ngx_command_t  ngx_mail_core_commands[] = {
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       offsetof(ngx_mail_core_srv_conf_t, resolver_timeout),
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       NULL },
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+    { ngx_string("max_errors"),
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+      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_TAKE1,
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+      ngx_conf_set_num_slot,
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+      NGX_MAIL_SRV_CONF_OFFSET,
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+      offsetof(ngx_mail_core_srv_conf_t, max_errors),
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+      NULL },
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+
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       ngx_null_command
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 };
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@@ -163,6 +170,8 @@ ngx_mail_core_create_srv_conf(ngx_conf_t *cf)
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     cscf->timeout = NGX_CONF_UNSET_MSEC;
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     cscf->resolver_timeout = NGX_CONF_UNSET_MSEC;
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+    cscf->max_errors = NGX_CONF_UNSET_UINT;
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+
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     cscf->resolver = NGX_CONF_UNSET_PTR;
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     cscf->file_name = cf->conf_file->file.name.data;
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@@ -182,6 +191,7 @@ ngx_mail_core_merge_srv_conf(ngx_conf_t *cf, void *parent, void *child)
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     ngx_conf_merge_msec_value(conf->resolver_timeout, prev->resolver_timeout,
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                               30000);
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+    ngx_conf_merge_uint_value(conf->max_errors, prev->max_errors, 5);
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     ngx_conf_merge_str_value(conf->server_name, prev->server_name, "");
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diff --git a/src/mail/ngx_mail_handler.c b/src/mail/ngx_mail_handler.c
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index 0aaa0e7..71b8151 100644
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--- a/src/mail/ngx_mail_handler.c
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+++ b/src/mail/ngx_mail_handler.c
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@@ -871,7 +871,20 @@ ngx_mail_read_command(ngx_mail_session_t *s, ngx_connection_t *c)
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         return NGX_MAIL_PARSE_INVALID_COMMAND;
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     }
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-    if (rc == NGX_IMAP_NEXT || rc == NGX_MAIL_PARSE_INVALID_COMMAND) {
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+    if (rc == NGX_MAIL_PARSE_INVALID_COMMAND) {
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+
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+        s->errors++;
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+
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+        if (s->errors >= cscf->max_errors) {
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+            ngx_log_error(NGX_LOG_INFO, c->log, 0,
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+                          "client sent too many invalid commands");
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+            s->quit = 1;
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+        }
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+
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+        return rc;
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+    }
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+
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+    if (rc == NGX_IMAP_NEXT) {
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         return rc;
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     }
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-- 
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2.31.1
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