vtysh: fixup incorrect read logic

If a daemon sent vtysh a response whose size satisfied

1 <= 4096 - (size % 4096) <= 2

vtysh would hang.

Signed-off-by: Quentin Young <qlyoung@cumulusnetworks.com>

diff --git a/vtysh/vtysh.c b/vtysh/vtysh.c
index a28eff823296f4b5271508b518f41c0bf0a0b223..2a998cf6449adb4d143cebb6ae6ac02ba81fbbab 100644 (file)
--- a/vtysh/vtysh.c
+++ b/vtysh/vtysh.c
@@ -141,21 +141,22 @@ static int vtysh_client_run(struct vtysh_client *vclient, const char *line,
 
                bufvalid += nread;
 
+               /*
+                * We expect string output from daemons, so instead of looking
+                * for the full 3 null bytes of the terminator, we check for
+                * just one instead and assume it is the first byte of the
+                * terminator. The presence of the full terminator is checked
+                * later.
+                */
                if (bufvalid - buf >= 4)
-                       end = memmem(bufvalid - 4, 4, terminator,
-                                    sizeof(terminator));
-
-               if (end && end + sizeof(terminator) + 1 > bufvalid)
-                       /* found \0\0\0 but return code hasn't been read yet */
-                       end = NULL;
-               if (end)
-                       ret = end[sizeof(terminator)];
+                       end = memmem(bufvalid - 4, 4, "\0", 1);
 
                /*
                 * calculate # bytes we have, up to & not including the
                 * terminator if present
                 */
                size_t textlen = (end ? end : bufvalid) - buf;
+               bool b = false;
 
                /* feed line processing callback if present */
                while (callback && bufvalid > buf && (end > buf || !end)) {
@@ -165,16 +166,37 @@ static int vtysh_client_run(struct vtysh_client *vclient, const char *line,
                                /* line break */
                                *eol++ = '\0';
                        else if (end == buf)
-                               /* no line break, end of input, no text left
-                                * before end
-                                * => don't insert an empty line at the end */
-                               break;
+                               /*
+                                * no line break, end of input, no text left
+                                * before end; nothing to write
+                                */
+                               b = true;
                        else if (end)
-                               /* no line break, end of input, but some text
-                                * left */
+                               /* no nl, end of input, but some text left */
                                eol = end;
-                       else
-                               /* continue reading */
+                       else if (bufvalid == buf + bufsz) {
+                               /*
+                                * no nl, no end of input, no buffer space;
+                                * realloc
+                                */
+                               char *new;
+
+                               bufsz *= 2;
+                               if (buf == stackbuf) {
+                                       new = XMALLOC(MTYPE_TMP, bufsz);
+                                       memcpy(new, stackbuf, sizeof(stackbuf));
+                               } else
+                                       new = XREALLOC(MTYPE_TMP, buf, bufsz);
+
+                               bufvalid = bufvalid - buf + new;
+                               buf = new;
+                               /* !end -> we won't be reading more data... */
+                               assert(end == NULL);
+                               b = true;
+                       } else
+                               b = true;
+
+                       if (b)
                                break;
 
                        /* eol is at line end now, either \n => \0 or \0\0\0 */
@@ -187,10 +209,7 @@ static int vtysh_client_run(struct vtysh_client *vclient, const char *line,
                        if (callback)
                                callback(cbarg, buf);
 
-                       if (eol == end)
-                               /* \n\0\0\0 */
-                               break;
-
+                       /* shift back data and adjust bufvalid */
                        memmove(buf, eol, bufvalid - eol);
                        bufvalid -= eol - buf;
                        if (end)
@@ -203,23 +222,28 @@ static int vtysh_client_run(struct vtysh_client *vclient, const char *line,
                                fwrite(buf, 1, textlen, fp);
                        memmove(buf, buf + textlen, bufvalid - buf - textlen);
                        bufvalid -= textlen;
+                       if (end)
+                               end -= textlen;
+
+                       /*
+                        * ----------------------------------------------------
+                        * At this point `buf` should be in one of two states:
+                        * - Empty (i.e. buf == bufvalid)
+                        * - Contains up to 4 bytes of the terminator
+                        * ----------------------------------------------------
+                        */
+                       assert(((buf == bufvalid)
+                               || (bufvalid - buf <= 4 && buf[0] == 0x00)));
                }
 
-               if (bufvalid == buf + bufsz) {
-                       char *new;
-                       bufsz *= 2;
-                       if (buf == stackbuf) {
-                               new = XMALLOC(MTYPE_TMP, bufsz);
-                               memcpy(new, stackbuf, sizeof(stackbuf));
-                       } else
-                               new = XREALLOC(MTYPE_TMP, buf, bufsz);
-
-                       bufvalid = bufvalid - buf + new;
-                       buf = new;
-                       /* if end != NULL, we won't be reading more data... */
-                       assert(end == NULL);
+               /* if we have the terminator, break */
+               if (end && bufvalid - buf == 4) {
+                       assert(!memcmp(buf, terminator, 3));
+                       ret = buf[3];
+                       break;
                }
-       } while (!end);
+
+       } while (true);
        goto out;
 
 out_err: