[PATCH] imap-send: increase command size limit

["René Scharfe" <l.s.r@web.de>]

nfvasprintf() has a 8KB limit, but it's not relevant, as its result is
combined with other strings and added to a 1KB buffer by its caller.
That 1KB limit is not mentioned in RFC 9051, which specifies IMAP.

While 1KB is plenty for user names, passwords and mailbox names,
there's no point in limiting our commands like that.  Call xstrvfmt()
instead of open-coding it and use strbuf to format the command to
send, as we need its length.  Fail hard if it exceeds INT_MAX, because
socket_write() can't take more than that.

Suggested-by: Jeff King <peff@peff.net>
Signed-off-by: René Scharfe <l.s.r@web.de>
---
This time I compiled with NO_CURL=1 and NO_APPLE_COMMON_CRYPTO=1 and
verified with a silly printf that the changed code was actually used
and wrote the present message to an IMAP folder whose name is 1006
characters log, which required a 1026 bytes long APPEND command.  Yay,
freedom!

Ran into a build issue, will send a separate patch for that.

 imap-send.c | 35 ++++++++++++-----------------------
 1 file changed, 12 insertions(+), 23 deletions(-)

diff --git a/imap-send.c b/imap-send.c
index 4caa8668e6..0afd088d8a 100644
--- a/imap-send.c
+++ b/imap-send.c
@@ -68,20 +68,6 @@ static void imap_warn(const char *, ...);

 static char *next_arg(char **);

-static int nfvasprintf(char **strp, const char *fmt, va_list ap)
-{
-	int len;
-	char tmp[8192];
-
-	len = vsnprintf(tmp, sizeof(tmp), fmt, ap);
-	if (len < 0)
-		die("Fatal: Out of memory");
-	if (len >= sizeof(tmp))
-		die("imap command overflow!");
-	*strp = xmemdupz(tmp, len);
-	return len;
-}
-
 struct imap_server_conf {
 	const char *name;
 	const char *tunnel;
@@ -503,11 +489,11 @@ static struct imap_cmd *issue_imap_cmd(struct imap_store *ctx,
 {
 	struct imap *imap = ctx->imap;
 	struct imap_cmd *cmd;
-	int n, bufl;
-	char buf[1024];
+	int n;
+	struct strbuf buf = STRBUF_INIT;

 	cmd = xmalloc(sizeof(struct imap_cmd));
-	nfvasprintf(&cmd->cmd, fmt, ap);
+	cmd->cmd = xstrvfmt(fmt, ap);
 	cmd->tag = ++imap->nexttag;

 	if (cb)
@@ -519,27 +505,30 @@ static struct imap_cmd *issue_imap_cmd(struct imap_store *ctx,
 		get_cmd_result(ctx, NULL);

 	if (!cmd->cb.data)
-		bufl = xsnprintf(buf, sizeof(buf), "%d %s\r\n", cmd->tag, cmd->cmd);
+		strbuf_addf(&buf, "%d %s\r\n", cmd->tag, cmd->cmd);
 	else
-		bufl = xsnprintf(buf, sizeof(buf), "%d %s{%d%s}\r\n",
-				 cmd->tag, cmd->cmd, cmd->cb.dlen,
-				 CAP(LITERALPLUS) ? "+" : "");
+		strbuf_addf(&buf, "%d %s{%d%s}\r\n", cmd->tag, cmd->cmd,
+			    cmd->cb.dlen, CAP(LITERALPLUS) ? "+" : "");
+	if (buf.len > INT_MAX)
+		die("imap command overflow!");

 	if (0 < verbosity) {
 		if (imap->num_in_progress)
 			printf("(%d in progress) ", imap->num_in_progress);
 		if (!starts_with(cmd->cmd, "LOGIN"))
-			printf(">>> %s", buf);
+			printf(">>> %s", buf.buf);
 		else
 			printf(">>> %d LOGIN <user> <pass>\n", cmd->tag);
 	}
-	if (socket_write(&imap->buf.sock, buf, bufl) != bufl) {
+	if (socket_write(&imap->buf.sock, buf.buf, buf.len) != buf.len) {
 		free(cmd->cmd);
 		free(cmd);
 		if (cb)
 			free(cb->data);
+		strbuf_release(&buf);
 		return NULL;
 	}
+	strbuf_release(&buf);
 	if (cmd->cb.data) {
 		if (CAP(LITERALPLUS)) {
 			n = socket_write(&imap->buf.sock, cmd->cb.data, cmd->cb.dlen);
--
2.44.0