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ui/vnc-clipboard: fix integer underflow in vnc_client_cut_text_ext

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Extended ClientCutText messages start with a 4-byte header. If len < 4,
an integer underflow occurs in vnc_client_cut_text_ext. The result is
used to decompress data in a while loop in inflate_buffer, leading to
CPU consumption and denial of service. Prevent this by checking dlen in
protocol_client_msg.

Fixes: CVE-2022-3165
Fixes: 0bf41cab93 ("ui/vnc: clipboard support")
Reported-by: TangPeng <tangpeng@qianxin.com>
Signed-off-by: Mauro Matteo Cascella <mcascell@redhat.com>
Message-Id: <20220925204511.1103214-1-mcascell@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
This commit is contained in:
Mauro Matteo Cascella 2022-09-25 22:45:11 +02:00 committed by Gerd Hoffmann
parent b6d93282cc
commit d307040b18
1 changed files with 8 additions and 3 deletions
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11
ui/vnc.c
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@ -2442,8 +2442,8 @@ static int protocol_client_msg(VncState *vs, uint8_t *data, size_t len)
if (len == 1) {
return 8;
}
uint32_t dlen = abs(read_s32(data, 4));
if (len == 8) {
uint32_t dlen = abs(read_s32(data, 4));
if (dlen > (1 << 20)) {
error_report("vnc: client_cut_text msg payload has %u bytes"
" which exceeds our limit of 1MB.", dlen);
@ -2456,8 +2456,13 @@ static int protocol_client_msg(VncState *vs, uint8_t *data, size_t len)
}
if (read_s32(data, 4) < 0) {
vnc_client_cut_text_ext(vs, abs(read_s32(data, 4)),
read_u32(data, 8), data + 12);
if (dlen < 4) {
error_report("vnc: malformed payload (header less than 4 bytes)"
" in extended clipboard pseudo-encoding.");
vnc_client_error(vs);
break;
}
vnc_client_cut_text_ext(vs, dlen, read_u32(data, 8), data + 12);
break;
}
vnc_client_cut_text(vs, read_u32(data, 4), data + 8);