From 68ccb8021a838066f0951d4b2817eb6b6f10a843 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Marc-Andr=C3=A9=20Lureau?= <marcandre.lureau@redhat.com>
Date: Mon, 27 Jan 2020 10:24:14 +0100
Subject: [PATCH] tcp_emu: fix unsafe snprintf() usages
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
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Various calls to snprintf() assume that snprintf() returns "only" the
number of bytes written (excluding terminating NUL).
https://pubs.opengroup.org/onlinepubs/9699919799/functions/snprintf.html#tag_16_159_04
"Upon successful completion, the snprintf() function shall return the
number of bytes that would be written to s had n been sufficiently
large excluding the terminating null byte."
Before patch ce131029, if there isn't enough room in "m_data" for the
"DCC ..." message, we overflow "m_data".
After the patch, if there isn't enough room for the same, we don't
overflow "m_data", but we set "m_len" out-of-bounds. The next time an
access is bounded by "m_len", we'll have a buffer overflow then.
Use slirp_fmt*() to fix potential OOB memory access.
Reported-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Message-Id: <20200127092414.169796-7-marcandre.lureau@redhat.com>
---
src/tcp_subr.c | 44 +++++++++++++++++++++-----------------------
1 file changed, 21 insertions(+), 23 deletions(-)
diff -up slirp4netns-4992082b2af77c09bca6bd8504e2ebfa5e118c18/qemu/slirp/src/tcp_subr.c.orig slirp4netns-4992082b2af77c09bca6bd8504e2ebfa5e118c18/qemu/slirp/src/tcp_subr.c
--- slirp4netns-4992082b2af77c09bca6bd8504e2ebfa5e118c18/qemu/slirp/src/tcp_subr.c.orig 2020-02-06 14:57:07.786013242 +0100
+++ slirp4netns-4992082b2af77c09bca6bd8504e2ebfa5e118c18/qemu/slirp/src/tcp_subr.c 2020-02-06 15:14:44.678746260 +0100
@@ -709,9 +709,9 @@ tcp_emu(struct socket *so, struct mbuf *
n4 = (laddr & 0xff);
m->m_len = bptr - m->m_data; /* Adjust length */
- m->m_len += snprintf(bptr, M_FREEROOM(m),
- "ORT %d,%d,%d,%d,%d,%d\r\n%s",
- n1, n2, n3, n4, n5, n6, x==7?buff:"");
+ m->m_len += slirp_fmt(bptr, M_FREEROOM(m),
+ "ORT %d,%d,%d,%d,%d,%d\r\n%s",
+ n1, n2, n3, n4, n5, n6, x == 7 ? buff : "");
return 1;
} else if ((bptr = (char *)strstr(m->m_data, "27 Entering")) != NULL) {
/*
@@ -742,10 +742,9 @@ tcp_emu(struct socket *so, struct mbuf *
n4 = (laddr & 0xff);
m->m_len = bptr - m->m_data; /* Adjust length */
- m->m_len += snprintf(bptr, M_FREEROOM(m),
- "27 Entering Passive Mode (%d,%d,%d,%d,%d,%d)\r\n%s",
- n1, n2, n3, n4, n5, n6, x==7?buff:"");
-
+ m->m_len += slirp_fmt(bptr, M_FREEROOM(m),
+ "27 Entering Passive Mode (%d,%d,%d,%d,%d,%d)\r\n%s",
+ n1, n2, n3, n4, n5, n6, x == 7 ? buff : "");
return 1;
}
@@ -768,9 +767,8 @@ tcp_emu(struct socket *so, struct mbuf *
if (m->m_data[m->m_len-1] == '\0' && lport != 0 &&
(so = tcp_listen(slirp, INADDR_ANY, 0, so->so_laddr.s_addr,
htons(lport), SS_FACCEPTONCE)) != NULL)
- m->m_len = snprintf(m->m_data, M_ROOM(m),
- "%d", ntohs(so->so_fport)) + 1;
-
+ m->m_len = slirp_fmt0(m->m_data, M_ROOM(m),
+ "%d", ntohs(so->so_fport));
return 1;
case EMU_IRC:
@@ -789,10 +787,10 @@ tcp_emu(struct socket *so, struct mbuf *
return 1;
}
m->m_len = bptr - m->m_data; /* Adjust length */
- m->m_len += snprintf(bptr, M_FREEROOM(m),
- "DCC CHAT chat %lu %u%c\n",
- (unsigned long)ntohl(so->so_faddr.s_addr),
- ntohs(so->so_fport), 1);
+ m->m_len += slirp_fmt(bptr, M_FREEROOM(m),
+ "DCC CHAT chat %lu %u%c\n",
+ (unsigned long)ntohl(so->so_faddr.s_addr),
+ ntohs(so->so_fport), 1);
} else if (sscanf(bptr, "DCC SEND %256s %u %u %u", buff, &laddr, &lport, &n1) == 4) {
if ((so = tcp_listen(slirp, INADDR_ANY, 0,
htonl(laddr), htons(lport),
@@ -800,10 +798,10 @@ tcp_emu(struct socket *so, struct mbuf *
return 1;
}
m->m_len = bptr - m->m_data; /* Adjust length */
- m->m_len += snprintf(bptr, M_FREEROOM(m),
- "DCC SEND %s %lu %u %u%c\n", buff,
- (unsigned long)ntohl(so->so_faddr.s_addr),
- ntohs(so->so_fport), n1, 1);
+ m->m_len += slirp_fmt(bptr, M_FREEROOM(m),
+ "DCC SEND %s %lu %u %u%c\n", buff,
+ (unsigned long)ntohl(so->so_faddr.s_addr),
+ ntohs(so->so_fport), n1, 1);
} else if (sscanf(bptr, "DCC MOVE %256s %u %u %u", buff, &laddr, &lport, &n1) == 4) {
if ((so = tcp_listen(slirp, INADDR_ANY, 0,
htonl(laddr), htons(lport),
@@ -811,10 +809,10 @@ tcp_emu(struct socket *so, struct mbuf *
return 1;
}
m->m_len = bptr - m->m_data; /* Adjust length */
- m->m_len += snprintf(bptr, M_FREEROOM(m),
- "DCC MOVE %s %lu %u %u%c\n", buff,
- (unsigned long)ntohl(so->so_faddr.s_addr),
- ntohs(so->so_fport), n1, 1);
+ m->m_len += slirp_fmt(bptr, M_FREEROOM(m),
+ "DCC MOVE %s %lu %u %u%c\n", buff,
+ (unsigned long)ntohl(so->so_faddr.s_addr),
+ ntohs(so->so_fport), n1, 1);
}
return 1;
From 30648c03b27fb8d9611b723184216cd3174b6775 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Marc-Andr=C3=A9=20Lureau?= <marcandre.lureau@redhat.com>
Date: Mon, 27 Jan 2020 10:24:09 +0100
Subject: [PATCH] util: add slirp_fmt() helpers
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Various calls to snprintf() in libslirp assume that snprintf() returns
"only" the number of bytes written (excluding terminating NUL).
https://pubs.opengroup.org/onlinepubs/9699919799/functions/snprintf.html#tag_16_159_04
"Upon successful completion, the snprintf() function shall return the
number of bytes that would be written to s had n been sufficiently
large excluding the terminating null byte."
Introduce slirp_fmt() that handles several pathological cases the
way libslirp usually expect:
- treat error as fatal (instead of silently returning -1)
- fmt0() will always \0 end
- return the number of bytes actually written (instead of what would
have been written, which would usually result in OOB later), including
the ending \0 for fmt0()
- warn if truncation happened (instead of ignoring)
Other less common cases can still be handled with strcpy/snprintf() etc.
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Message-Id: <20200127092414.169796-2-marcandre.lureau@redhat.com>
---
src/util.c | 62 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
src/util.h | 3 +++
2 files changed, 65 insertions(+)
diff -up slirp4netns-4992082b2af77c09bca6bd8504e2ebfa5e118c18/qemu/slirp/src/util.c.orig slirp4netns-4992082b2af77c09bca6bd8504e2ebfa5e118c18/qemu/slirp/src/util.c
--- slirp4netns-4992082b2af77c09bca6bd8504e2ebfa5e118c18/qemu/slirp/src/util.c.orig 2019-03-28 12:45:09.000000000 +0100
+++ slirp4netns-4992082b2af77c09bca6bd8504e2ebfa5e118c18/qemu/slirp/src/util.c 2020-02-06 14:57:07.786013242 +0100
@@ -366,3 +366,65 @@ void slirp_pstrcpy(char *buf, int buf_si
}
*q = '\0';
}
+
+static int slirp_vsnprintf(char *str, size_t size,
+ const char *format, va_list args)
+{
+ int rv = vsnprintf(str, size, format, args);
+
+ if (rv < 0) {
+ g_error("vsnprintf() failed: %s", g_strerror(errno));
+ }
+
+ return rv;
+}
+
+/*
+ * A snprintf()-like function that:
+ * - returns the number of bytes written (excluding optional \0-ending)
+ * - dies on error
+ * - warn on truncation
+ */
+int slirp_fmt(char *str, size_t size, const char *format, ...)
+{
+ va_list args;
+ int rv;
+
+ va_start(args, format);
+ rv = slirp_vsnprintf(str, size, format, args);
+ va_end(args);
+
+ if (rv > size) {
+ g_critical("vsnprintf() truncation");
+ }
+
+ return MIN(rv, size);
+}
+
+/*
+ * A snprintf()-like function that:
+ * - always \0-end (unless size == 0)
+ * - returns the number of bytes actually written, including \0 ending
+ * - dies on error
+ * - warn on truncation
+ */
+int slirp_fmt0(char *str, size_t size, const char *format, ...)
+{
+ va_list args;
+ int rv;
+
+ va_start(args, format);
+ rv = slirp_vsnprintf(str, size, format, args);
+ va_end(args);
+
+ if (rv >= size) {
+ g_critical("vsnprintf() truncation");
+ if (size > 0)
+ str[size - 1] = '\0';
+ rv = size;
+ } else {
+ rv += 1; /* include \0 */
+ }
+
+ return rv;
+}
diff -up slirp4netns-4992082b2af77c09bca6bd8504e2ebfa5e118c18/qemu/slirp/src/util.h.orig slirp4netns-4992082b2af77c09bca6bd8504e2ebfa5e118c18/qemu/slirp/src/util.h
--- slirp4netns-4992082b2af77c09bca6bd8504e2ebfa5e118c18/qemu/slirp/src/util.h.orig 2019-03-28 12:45:09.000000000 +0100
+++ slirp4netns-4992082b2af77c09bca6bd8504e2ebfa5e118c18/qemu/slirp/src/util.h 2020-02-06 14:57:07.786013242 +0100
@@ -172,4 +172,7 @@ static inline int slirp_socket_set_fast_
void slirp_pstrcpy(char *buf, int buf_size, const char *str);
+int slirp_fmt(char *str, size_t size, const char *format, ...);
+int slirp_fmt0(char *str, size_t size, const char *format, ...);
+
#endif