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SUSE:SLE-12-SP4:Update
xen.16559
CVE-2020-8608-qemut-tcp_emu-fix-unsafe-snprintf...
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File CVE-2020-8608-qemut-tcp_emu-fix-unsafe-snprintf-usages.patch of Package xen.16559
Subject: util: add slirp_fmt() helpers From: Marc-André Lureau marcandre.lureau@redhat.com Mon Jan 27 10:24:09 2020 +0100 Date: Mon Jan 27 10:28:43 2020 +0100: Git: 30648c03b27fb8d9611b723184216cd3174b6775 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> Subject: tcp_emu: fix unsafe snprintf() usages From: Marc-André Lureau marcandre.lureau@redhat.com Mon Jan 27 10:24:14 2020 +0100 Date: Mon Jan 27 10:28:43 2020 +0100: Git: 68ccb8021a838066f0951d4b2817eb6b6f10a843 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> Index: xen-4.7.6-testing/tools/qemu-xen-traditional-dir-remote/slirp/tcp_subr.c =================================================================== --- xen-4.7.6-testing.orig/tools/qemu-xen-traditional-dir-remote/slirp/tcp_subr.c +++ xen-4.7.6-testing/tools/qemu-xen-traditional-dir-remote/slirp/tcp_subr.c @@ -595,6 +595,68 @@ tcp_tos(so) int do_echo = -1; #endif +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 + */ +static 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 + */ +static 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; +} + /* * Emulate programs that try and connect to us * This includes ftp (the data connection is @@ -673,7 +735,7 @@ tcp_emu(so, m) break; } } - so_rcv->sb_cc = snprintf(so_rcv->sb_data, + so_rcv->sb_cc = slirp_fmt(so_rcv->sb_data, so_rcv->sb_datalen, "%d,%d\r\n", n1, n2); so_rcv->sb_rptr = so_rcv->sb_data; @@ -1010,7 +1072,7 @@ do_prompt: n4 = (laddr & 0xff); m->m_len = bptr - m->m_data; /* Adjust length */ - m->m_len += snprintf(bptr, m->m_hdr.mh_size - m->m_len, + m->m_len += slirp_fmt(bptr, m->m_hdr.mh_size - m->m_len, "ORT %d,%d,%d,%d,%d,%d\r\n%s", n1, n2, n3, n4, n5, n6, x==7?buff:""); return 1; @@ -1042,7 +1104,7 @@ do_prompt: n4 = (laddr & 0xff); m->m_len = bptr - m->m_data; /* Adjust length */ - m->m_len += snprintf(bptr, m->m_hdr.mh_size - m->m_len, + m->m_len += slirp_fmt(bptr, m->m_hdr.mh_size - m->m_len, "27 Entering Passive Mode (%d,%d,%d,%d,%d,%d)\r\n%s", n1, n2, n3, n4, n5, n6, x==7?buff:""); @@ -1067,7 +1129,7 @@ do_prompt: } if (m->m_data[m->m_len-1] == '\0' && lport != 0 && (so = solisten(0, so->so_laddr.s_addr, htons(lport), SS_FACCEPTONCE)) != NULL) - m->m_len = snprintf(m->m_data, m->m_hdr.mh_size, "%d", + m->m_len = slirp_fmt0(m->m_data, m->m_hdr.mh_size, "%d", ntohs(so->so_fport)) + 1; return 1; @@ -1085,7 +1147,7 @@ do_prompt: return 1; m->m_len = bptr - m->m_data; /* Adjust length */ - m->m_len += snprintf(bptr, m->m_hdr.mh_size, + m->m_len += slirp_fmt(bptr, m->m_hdr.mh_size, "DCC CHAT chat %lu %u%c\n", (unsigned long)ntohl(so->so_faddr.s_addr), ntohs(so->so_fport), 1); @@ -1094,7 +1156,7 @@ do_prompt: return 1; m->m_len = bptr - m->m_data; /* Adjust length */ - m->m_len += snprintf(bptr, m->m_hdr.mh_size, + m->m_len += slirp_fmt(bptr, m->m_hdr.mh_size, "DCC SEND %s %lu %u %u%c\n", buff, (unsigned long)ntohl(so->so_faddr.s_addr), ntohs(so->so_fport), n1, 1); @@ -1103,7 +1165,7 @@ do_prompt: return 1; m->m_len = bptr - m->m_data; /* Adjust length */ - m->m_len += snprintf(bptr, m->m_hdr.mh_size, + m->m_len += slirp_fmt(bptr, m->m_hdr.mh_size, "DCC MOVE %s %lu %u %u%c\n", buff, (unsigned long)ntohl(so->so_faddr.s_addr), ntohs(so->so_fport), n1, 1); @@ -1299,7 +1361,7 @@ tcp_ctl(so) /* FALLTHROUGH */ case CTL_ALIAS: - sb->sb_cc = snprintf(sb->sb_wptr, sb->sb_datalen - (sb->sb_wptr - sb->sb_data), + sb->sb_cc = slirp_fmt(sb->sb_wptr, sb->sb_datalen - (sb->sb_wptr - sb->sb_data), "Error: No application configured.\r\n"); sb->sb_wptr += sb->sb_cc; return(0);
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