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ftp: reject illegal IP/port in PASV 227 response

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... by using range checks. Among other things, this avoids an undefined
behavior for a left shift that could happen on negative or very large
values.

Closes #1997

Detected by OSS-fuzz: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=3694
This commit is contained in:
Daniel Stenberg 2017-10-19 14:41:14 +02:00
parent 8351ab4510
commit 769647e714
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GPG key ID: 5CC908FDB71E12C2
2 changed files with 7 additions and 10 deletions
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9
lib/ftp.c
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@ -1874,8 +1874,8 @@ static CURLcode ftp_state_pasv_resp(struct connectdata *conn,
else if((ftpc->count1 == 1) &&
(ftpcode == 227)) {
/* positive PASV response */
int ip[4];
int port[2];
unsigned int ip[4];
unsigned int port[2];
/*
* Scan for a sequence of six comma-separated numbers and use them as
@ -1887,14 +1887,15 @@ static CURLcode ftp_state_pasv_resp(struct connectdata *conn,
* "227 Entering passive mode. 127,0,0,1,4,51"
*/
while(*str) {
if(6 == sscanf(str, "%d,%d,%d,%d,%d,%d",
if(6 == sscanf(str, "%u,%u,%u,%u,%u,%u",
&ip[0], &ip[1], &ip[2], &ip[3],
&port[0], &port[1]))
break;
str++;
}
if(!*str) {
if(!*str || (ip[0] > 255) || (ip[1] > 255) || (ip[2] > 255) ||
(ip[3] > 255) || (port[0] > 255) || (port[1] > 255) ) {
failf(data, "Couldn't interpret the 227-response");
return CURLE_FTP_WEIRD_227_FORMAT;
}