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Fix potential double-free() in Interactive Service (CVE-2018-9336)

Malformed input data on the service pipe towards the OpenVPN interactive
service (normally used by the OpenVPN GUI to request openvpn instances
from the service) can result in a double free() in the error handling code.

This usually only leads to a process crash (DoS by an unprivileged local
account) but since it could possibly lead to memory corruption if
happening while multiple other threads are active at the same time,
CVE-2018-9336 has been assigned to acknowledge this risk.

Fix by ensuring that sud->directory is set to NULL in GetStartUpData()
for all error cases (thus not being free()ed in FreeStartupData()).

Rewrite control flow to use explicit error label for error exit.

Discovered and reported by Jacob Baines <jbaines@tenable.com>.

CVE: 2018-9336

Signed-off-by: Gert Doering <gert@greenie.muc.de>
Acked-by: Selva Nair <selva.nair@gmail.com>
Message-Id: <20180414072617.25075-1-gert@greenie.muc.de>
URL: https://www.mail-archive.com/search?l=mid&q=20180414072617.25075-1-gert@greenie.muc.de

Signed-off-by: Gert Doering <gert@greenie.muc.de>
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cron2 committed Apr 14, 2018
1 parent 8acc40b commit 1394192b210cb3c6624a7419bcf3ff966742e79b
Showing with 11 additions and 12 deletions.
  1. +11 −12 src/openvpnserv/interactive.c
@@ -453,7 +453,6 @@ static BOOL
GetStartupData(HANDLE pipe, STARTUP_DATA *sud)
{
size_t size, len;
BOOL ret = FALSE;
WCHAR *data = NULL;
DWORD bytes, read;
@@ -462,38 +461,38 @@ GetStartupData(HANDLE pipe, STARTUP_DATA *sud)
{
MsgToEventLog(M_SYSERR, TEXT("PeekNamedPipeAsync failed"));
ReturnLastError(pipe, L"PeekNamedPipeAsync");
goto out;
goto err;
}
size = bytes / sizeof(*data);
if (size == 0)
{
MsgToEventLog(M_SYSERR, TEXT("malformed startup data: 1 byte received"));
ReturnError(pipe, ERROR_STARTUP_DATA, L"GetStartupData", 1, &exit_event);
goto out;
goto err;
}
data = malloc(bytes);
if (data == NULL)
{
MsgToEventLog(M_SYSERR, TEXT("malloc failed"));
ReturnLastError(pipe, L"malloc");
goto out;
goto err;
}
read = ReadPipeAsync(pipe, data, bytes, 1, &exit_event);
if (bytes != read)
{
MsgToEventLog(M_SYSERR, TEXT("ReadPipeAsync failed"));
ReturnLastError(pipe, L"ReadPipeAsync");
goto out;
goto err;
}
if (data[size - 1] != 0)
{
MsgToEventLog(M_ERR, TEXT("Startup data is not NULL terminated"));
ReturnError(pipe, ERROR_STARTUP_DATA, L"GetStartupData", 1, &exit_event);
goto out;
goto err;
}
sud->directory = data;
@@ -503,7 +502,7 @@ GetStartupData(HANDLE pipe, STARTUP_DATA *sud)
{
MsgToEventLog(M_ERR, TEXT("Startup data ends at working directory"));
ReturnError(pipe, ERROR_STARTUP_DATA, L"GetStartupData", 1, &exit_event);
goto out;
goto err;
}
sud->options = sud->directory + len;
@@ -513,16 +512,16 @@ GetStartupData(HANDLE pipe, STARTUP_DATA *sud)
{
MsgToEventLog(M_ERR, TEXT("Startup data ends at command line options"));
ReturnError(pipe, ERROR_STARTUP_DATA, L"GetStartupData", 1, &exit_event);
goto out;
goto err;
}
sud->std_input = sud->options + len;
data = NULL; /* don't free data */
ret = TRUE;
return TRUE;
out:
err:
sud->directory = NULL; /* caller must not free() */
free(data);
return ret;
return FALSE;
}

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