File tcp_emu-fix-unsafe-snprintf-usages.patch of Package qemu

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File tcp_emu-fix-unsafe-snprintf-usages.patch of Package qemu (Revision 6afe152f32878fd4b230f887d23acf61)

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From: =?UTF-8?q?Marc-Andr=C3=A9=20Lureau?= <marcandre.lureau@redhat.com>
Date: Mon, 27 Jan 2020 10:24:14 +0100
Subject: tcp_emu: fix unsafe snprintf() usages
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Git-commit: 68ccb8021a838066f0951d4b2817eb6b6f10a843
References: bsc#1163018, CVE-2020-8608

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>
Signed-off-by: Bruce Rogers <brogers@suse.com>
---
 src/tcp_subr.c | 44 +++++++++++++++++++++-----------------------
 1 file changed, 21 insertions(+), 23 deletions(-)

diff --git a/slirp/src/tcp_subr.c b/slirp/src/tcp_subr.c
index 954d1a6f5e6292b585638a8c0558..26d4ead543a5357577817b39a3d6 100644
--- a/slirp/src/tcp_subr.c
+++ b/slirp/src/tcp_subr.c
@@ -655,8 +655,7 @@ int tcp_emu(struct socket *so, struct mbuf *m)
                 NTOHS(n1);
                 NTOHS(n2);
                 m_inc(m, snprintf(NULL, 0, "%d,%d\r\n", n1, n2) + 1);
-                m->m_len = snprintf(m->m_data, M_ROOM(m), "%d,%d\r\n", n1, n2);
-                assert(m->m_len < M_ROOM(m));
+                m->m_len = slirp_fmt(m->m_data, M_ROOM(m), "%d,%d\r\n", n1, n2);
             } else {
                 *eol = '\r';
             }
@@ -696,9 +695,9 @@ int tcp_emu(struct socket *so, struct mbuf *m)
             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) {
             /*
@@ -731,10 +730,9 @@ int tcp_emu(struct socket *so, struct mbuf *m)
             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;
         }
 
@@ -757,8 +755,8 @@ int tcp_emu(struct socket *so, struct mbuf *m)
         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:
@@ -777,10 +775,10 @@ int tcp_emu(struct socket *so, struct mbuf *m)
                 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),
@@ -788,10 +786,10 @@ int tcp_emu(struct socket *so, struct mbuf *m)
                 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),
@@ -799,10 +797,10 @@ int tcp_emu(struct socket *so, struct mbuf *m)
                 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;

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File tcp_emu-fix-unsafe-snprintf-usages.patch of Package qemu (Revision 6afe152f32878fd4b230f887d23acf61)

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