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SUSE:SLE-12-SP2:GA
xen.5575
CVE-2015-1779-qemuu-incrementally-decode-websoc...
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File CVE-2015-1779-qemuu-incrementally-decode-websocket-frames.patch of Package xen.5575
References: bsc#962632 CVE-2015-1779 Subject: CVE-2015-1779: incrementally decode websocket frames From: Daniel P. Berrange berrange@redhat.com Mon Mar 23 22:58:21 2015 +0000 Date: Wed Apr 1 17:11:34 2015 +0200: Git: a2bebfd6e09d285aa793cae3fb0fc3a39a9fee6e The logic for decoding websocket frames wants to fully decode the frame header and payload, before allowing the VNC server to see any of the payload data. There is no size limit on websocket payloads, so this allows a malicious network client to consume 2^64 bytes in memory in QEMU. It can trigger this denial of service before the VNC server even performs any authentication. The fix is to decode the header, and then incrementally decode the payload data as it is needed. With this fix the websocket decoder will allow at most 4k of data to be buffered before decoding and processing payload. Signed-off-by: Daniel P. Berrange <berrange@redhat.com> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com> Index: xen-4.5.2-testing/tools/qemu-xen-dir-remote/ui/vnc-ws.c =================================================================== --- xen-4.5.2-testing.orig/tools/qemu-xen-dir-remote/ui/vnc-ws.c +++ xen-4.5.2-testing/tools/qemu-xen-dir-remote/ui/vnc-ws.c @@ -115,7 +115,7 @@ long vnc_client_read_ws(VncState *vs) { int ret, err; uint8_t *payload; - size_t payload_size, frame_size; + size_t payload_size, header_size; VNC_DEBUG("Read websocket %p size %zd offset %zd\n", vs->ws_input.buffer, vs->ws_input.capacity, vs->ws_input.offset); buffer_reserve(&vs->ws_input, 4096); @@ -125,18 +125,39 @@ long vnc_client_read_ws(VncState *vs) } vs->ws_input.offset += ret; - /* make sure that nothing is left in the ws_input buffer */ + ret = 0; + /* consume as much of ws_input buffer as possible */ do { - err = vncws_decode_frame(&vs->ws_input, &payload, - &payload_size, &frame_size); - if (err <= 0) { - return err; + if (vs->ws_payload_remain == 0) { + err = vncws_decode_frame_header(&vs->ws_input, + &header_size, + &vs->ws_payload_remain, + &vs->ws_payload_mask); + if (err <= 0) { + return err; + } + + buffer_advance(&vs->ws_input, header_size); } + if (vs->ws_payload_remain != 0) { + err = vncws_decode_frame_payload(&vs->ws_input, + &vs->ws_payload_remain, + &vs->ws_payload_mask, + &payload, + &payload_size); + if (err < 0) { + return err; + } + if (err == 0) { + return ret; + } + ret += err; - buffer_reserve(&vs->input, payload_size); - buffer_append(&vs->input, payload, payload_size); + buffer_reserve(&vs->input, payload_size); + buffer_append(&vs->input, payload, payload_size); - buffer_advance(&vs->ws_input, frame_size); + buffer_advance(&vs->ws_input, payload_size); + } } while (vs->ws_input.offset > 0); return ret; @@ -274,15 +295,14 @@ void vncws_encode_frame(Buffer *output, buffer_append(output, payload, payload_size); } -int vncws_decode_frame(Buffer *input, uint8_t **payload, - size_t *payload_size, size_t *frame_size) +int vncws_decode_frame_header(Buffer *input, + size_t *header_size, + size_t *payload_remain, + WsMask *payload_mask) { unsigned char opcode = 0, fin = 0, has_mask = 0; - size_t header_size = 0; - uint32_t *payload32; + size_t payload_len; WsHeader *header = (WsHeader *)input->buffer; - WsMask mask; - int i; if (input->offset < WS_HEAD_MIN_LEN + 4) { /* header not complete */ @@ -292,7 +312,7 @@ int vncws_decode_frame(Buffer *input, ui fin = (header->b0 & 0x80) >> 7; opcode = header->b0 & 0x0f; has_mask = (header->b1 & 0x80) >> 7; - *payload_size = header->b1 & 0x7f; + payload_len = header->b1 & 0x7f; if (opcode == WS_OPCODE_CLOSE) { /* disconnect */ @@ -309,40 +329,57 @@ int vncws_decode_frame(Buffer *input, ui return -2; } - if (*payload_size < 126) { - header_size = 6; - mask = header->u.m; - } else if (*payload_size == 126 && input->offset >= 8) { - *payload_size = be16_to_cpu(header->u.s16.l16); - header_size = 8; - mask = header->u.s16.m16; - } else if (*payload_size == 127 && input->offset >= 14) { - *payload_size = be64_to_cpu(header->u.s64.l64); - header_size = 14; - mask = header->u.s64.m64; + if (payload_len < 126) { + *payload_remain = payload_len; + *header_size = 6; + *payload_mask = header->u.m; + } else if (payload_len == 126 && input->offset >= 8) { + *payload_remain = be16_to_cpu(header->u.s16.l16); + *header_size = 8; + *payload_mask = header->u.s16.m16; + } else if (payload_len == 127 && input->offset >= 14) { + *payload_remain = be64_to_cpu(header->u.s64.l64); + *header_size = 14; + *payload_mask = header->u.s64.m64; } else { /* header not complete */ return 0; } - *frame_size = header_size + *payload_size; + return 1; +} - if (input->offset < *frame_size) { - /* frame not complete */ +int vncws_decode_frame_payload(Buffer *input, + size_t *payload_remain, WsMask *payload_mask, + uint8_t **payload, size_t *payload_size) +{ + size_t i; + uint32_t *payload32; + + *payload = input->buffer; + /* If we aren't at the end of the payload, then drop + * off the last bytes, so we're always multiple of 4 + * for purpose of unmasking, except at end of payload + */ + if (input->offset < *payload_remain) { + *payload_size = input->offset - (input->offset % 4); + } else { + *payload_size = *payload_remain; + } + if (*payload_size == 0) { return 0; } - - *payload = input->buffer + header_size; + *payload_remain -= *payload_size; /* unmask frame */ /* process 1 frame (32 bit op) */ payload32 = (uint32_t *)(*payload); for (i = 0; i < *payload_size / 4; i++) { - payload32[i] ^= mask.u; + payload32[i] ^= payload_mask->u; } /* process the remaining bytes (if any) */ for (i *= 4; i < *payload_size; i++) { - (*payload)[i] ^= mask.c[i % 4]; + (*payload)[i] ^= payload_mask->c[i % 4]; } return 1; Index: xen-4.5.2-testing/tools/qemu-xen-dir-remote/ui/vnc-ws.h =================================================================== --- xen-4.5.2-testing.orig/tools/qemu-xen-dir-remote/ui/vnc-ws.h +++ xen-4.5.2-testing/tools/qemu-xen-dir-remote/ui/vnc-ws.h @@ -83,7 +83,12 @@ long vnc_client_read_ws(VncState *vs); void vncws_process_handshake(VncState *vs, uint8_t *line, size_t size); void vncws_encode_frame(Buffer *output, const void *payload, const size_t payload_size); -int vncws_decode_frame(Buffer *input, uint8_t **payload, - size_t *payload_size, size_t *frame_size); +int vncws_decode_frame_header(Buffer *input, + size_t *header_size, + size_t *payload_remain, + WsMask *payload_mask); +int vncws_decode_frame_payload(Buffer *input, + size_t *payload_remain, WsMask *payload_mask, + uint8_t **payload, size_t *payload_size); #endif /* __QEMU_UI_VNC_WS_H */ Index: xen-4.5.2-testing/tools/qemu-xen-dir-remote/ui/vnc.h =================================================================== --- xen-4.5.2-testing.orig/tools/qemu-xen-dir-remote/ui/vnc.h +++ xen-4.5.2-testing/tools/qemu-xen-dir-remote/ui/vnc.h @@ -299,6 +299,8 @@ struct VncState #ifdef CONFIG_VNC_WS Buffer ws_input; Buffer ws_output; + size_t ws_payload_remain; + WsMask ws_payload_mask; #endif /* current output mode information */ VncWritePixels *write_pixels;
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