From: Eugene Syromyatnikov <evgsyr@gmail.com>
Date: Mon, 10 Oct 2016 16:55:54 +0000 (+0300)
Subject: util: add support for QUOTE_0_TERMINATED in user_style to ptrintstr_ex
X-Git-Tag: v4.15~150
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=fdd97aac538f70c0425cd4380f46996f9cb7d2cf;p=strace

util: add support for QUOTE_0_TERMINATED in user_style to ptrintstr_ex

This enables printing size-limited (expectedly) ASCIZ strings.

This is done by increasing umoven size limit for sized strings by one
byte above max_strlen (enabling copying possible NUL byte in case len is
greater than max_strlen) and decreasing size after copying by one byte
in case QUOTE_0_TERMINATED is set (due to user_style or usage of len of
-1).  As a result, there is one excess byte for string_quote in case
QUOTE_0_TERMINATED is set so string_quote can check for NUL termination
of strings up to size bytes in size (which is len or max_strlen, whatever
is greater).

The catch here is that when string is not properly NUL-terminated and
QUOTE_0_TERMINATED is provided in user_style and len is less than
max_strlen then last non-NUL byte is not printed.  But ellipsis is
printed instead, being indication that string is not terminated
properly.  QUOTE_OMIT_TRAILING_0 should be used instead in case this
behaviour is not intended.

* util.c (printstr_ex): Copy one excess byte in case of non-negative len
provided and it is more than max_strlen; handle case of max_strlen of 0
in case QUOTE_0_TERMINATED is set separately; check for need of printing
ellipsis by checking resulting style against QUOTE_0_TERMINATED.
---

diff --git a/util.c b/util.c
index 05c0e15c..f895f227 100644
--- a/util.c
+++ b/util.c
@@ -838,13 +838,13 @@ printstr_ex(struct tcb *tcp, long addr, long len, unsigned int user_style)
 		outstr = xmalloc(outstr_size);
 	}
 
-	size = max_strlen;
+	size = max_strlen + 1;
 	if (len == -1) {
 		/*
 		 * Treat as a NUL-terminated string: fetch one byte more
 		 * because string_quote may look one byte ahead.
 		 */
-		if (umovestr(tcp, addr, size + 1, str) < 0) {
+		if (umovestr(tcp, addr, size, str) < 0) {
 			printaddr(addr);
 			return;
 		}
@@ -862,11 +862,23 @@ printstr_ex(struct tcb *tcp, long addr, long len, unsigned int user_style)
 
 	style |= user_style;
 
+	if (style & QUOTE_0_TERMINATED) {
+		if (size) {
+			--size;
+		} else {
+			tprints((len == -1) || (len == 0) ? "\"\"" : "\"\"...");
+			return;
+		}
+	}
+	if (size > max_strlen)
+		size = max_strlen;
+
 	/* If string_quote didn't see NUL and (it was supposed to be ASCIZ str
 	 * or we were requested to print more than -s NUM chars)...
 	 */
 	ellipsis = (string_quote(str, outstr, size, style) &&
-			(len < 0 || (unsigned long) len > max_strlen));
+			((style & QUOTE_0_TERMINATED) ||
+				(unsigned long) len > max_strlen));
 
 	tprints(outstr);
 	if (ellipsis)