git: 5760cb266e0a - main - Fix CVE-2020-10188

[Cy Schubert]

The branch main has been updated by cy:

URL: 
https://cgit.FreeBSD.org/src/commit/?id=5760cb266e0ab04c221c2acdb4b6c4c141130ecd

commit 5760cb266e0ab04c221c2acdb4b6c4c141130ecd
Author:     Cy Schubert <c...@freebsd.org>
AuthorDate: 2022-09-21 21:38:08 +0000
Commit:     Cy Schubert <c...@freebsd.org>
CommitDate: 2022-09-27 17:36:13 +0000

    Fix CVE-2020-10188
    
    Reviewed by:            emaste
    Obtained from:          NetBSD 6cc1539c8028b
    MFC after:              3 days
    Differential Revision:  https://reviews.freebsd.org/D36732
---
 contrib/telnet/telnetd/utility.c | 32 +++++++++++++++++++++-----------
 1 file changed, 21 insertions(+), 11 deletions(-)

diff --git a/contrib/telnet/telnetd/utility.c b/contrib/telnet/telnetd/utility.c
index 1ad51c55b177..2e1f61fd5bd9 100644
--- a/contrib/telnet/telnetd/utility.c
+++ b/contrib/telnet/telnetd/utility.c
@@ -147,31 +147,38 @@ ptyflush(void)
  * character.
  */
 static char *
-nextitem(char *current)
+nextitem(char *current, const char *endp)
 {
+    if (current >= endp) {
+       return NULL;
+    }
     if ((*current&0xff) != IAC) {
        return current+1;
     }
+    if (current+1 >= endp) {
+       return NULL;
+    }
     switch (*(current+1)&0xff) {
     case DO:
     case DONT:
     case WILL:
     case WONT:
-       return current+3;
+       return current+3 <= endp ? current+3 : NULL;
     case SB:           /* loop forever looking for the SE */
        {
            char *look = current+2;
 
-           for (;;) {
+           while (look < endp) {
                if ((*look++&0xff) == IAC) {
-                   if ((*look++&0xff) == SE) {
+                   if (look < endp && (*look++&0xff) == SE) {
                        return look;
                    }
                }
            }
+           return NULL;
        }
     default:
-       return current+2;
+       return current+2 <= endp ? current+2 : NULL;
     }
 }  /* end of nextitem */
 
@@ -197,7 +204,7 @@ netclear(void)
     char *thisitem, *next;
     char *good;
 #define        wewant(p)       ((nfrontp > p) && ((*p&0xff) == IAC) && \
-                               ((*(p+1)&0xff) != EC) && ((*(p+1)&0xff) != EL))
+                               (nfrontp > p+1) && ((*(p+1)&0xff) != EC) && 
((*(p+1)&0xff) != EL))
 
 #ifdef ENCRYPTION
     thisitem = nclearto > netobuf ? nclearto : netobuf;
@@ -205,7 +212,7 @@ netclear(void)
     thisitem = netobuf;
 #endif /* ENCRYPTION */
 
-    while ((next = nextitem(thisitem)) <= nbackp) {
+    while ((next = nextitem(thisitem, nbackp)) != NULL && (next <= nbackp)) {
        thisitem = next;
     }
 
@@ -217,20 +224,23 @@ netclear(void)
     good = netobuf;    /* where the good bytes go */
 #endif /* ENCRYPTION */
 
-    while (nfrontp > thisitem) {
+    while ((thisitem != NULL) && (nfrontp > thisitem)) {
        if (wewant(thisitem)) {
            int length;
 
            next = thisitem;
            do {
-               next = nextitem(next);
-           } while (wewant(next) && (nfrontp > next));
+               next = nextitem(next, nfrontp);
+           } while ((next != NULL) && wewant(next) && (nfrontp > next));
+           if (next == NULL) {
+               next = nfrontp;
+           }
            length = next-thisitem;
            memmove(good, thisitem, length);
            good += length;
            thisitem = next;
        } else {
-           thisitem = nextitem(thisitem);
+           thisitem = nextitem(thisitem, nfrontp);
        }
     }