X-Git-Url: https://asedeno.scripts.mit.edu/gitweb/?a=blobdiff_plain;f=misc.c;h=01bb32ee9c19c0d8575162808d5c0012203809a6;hb=refs%2Fheads%2Fbranch-0.56;hp=78d829a9b4ecfb8cafdbc648e73d12fd499ef9c9;hpb=0a293ae208d67f708c5d06db0d2707d717ff836d;p=PuTTY.git

diff --git a/misc.c b/misc.c
index 78d829a9..01bb32ee 100644
--- a/misc.c
+++ b/misc.c
@@ -1,6 +1,11 @@
+/*
+ * Platform-independent routines shared between all PuTTY programs.
+ */
+
 #include <stdio.h>
 #include <stdlib.h>
 #include <stdarg.h>
+#include <limits.h>
 #include <ctype.h>
 #include <assert.h>
 #include "putty.h"
@@ -57,13 +62,46 @@ char *dupcat(const char *s1, ...)
 /*
  * Do an sprintf(), but into a custom-allocated buffer.
  * 
- * Irritatingly, we don't seem to be able to do this portably using
- * vsnprintf(), because there appear to be issues with re-using the
- * same va_list for two calls, and the excellent C99 va_copy is not
- * yet widespread. Bah. Instead I'm going to do a horrid, horrid
- * hack, in which I trawl the format string myself, work out the
- * maximum length of each format component, and resize the buffer
- * before printing it.
+ * Currently I'm doing this via vsnprintf. This has worked so far,
+ * but it's not good, because:
+ * 
+ *  - vsnprintf is not available on all platforms. There's an ifdef
+ *    to use `_vsnprintf', which seems to be the local name for it
+ *    on Windows. Other platforms may lack it completely, in which
+ *    case it'll be time to rewrite this function in a totally
+ *    different way.
+ * 
+ *  - technically you can't reuse a va_list like this: it is left
+ *    unspecified whether advancing a va_list pointer modifies its
+ *    value or something it points to, so on some platforms calling
+ *    vsnprintf twice on the same va_list might fail hideously. It
+ *    would be better to use the `va_copy' macro mandated by C99,
+ *    but that too is not yet ubiquitous.
+ * 
+ * The only `properly' portable solution I can think of is to
+ * implement my own format string scanner, which figures out an
+ * upper bound for the length of each formatting directive,
+ * allocates the buffer as it goes along, and calls sprintf() to
+ * actually process each directive. If I ever need to actually do
+ * this, some caveats:
+ * 
+ *  - It's very hard to find a reliable upper bound for
+ *    floating-point values. %f, in particular, when supplied with
+ *    a number near to the upper or lower limit of representable
+ *    numbers, could easily take several hundred characters. It's
+ *    probably feasible to predict this statically using the
+ *    constants in <float.h>, or even to predict it dynamically by
+ *    looking at the exponent of the specific float provided, but
+ *    it won't be fun.
+ * 
+ *  - Don't forget to _check_, after calling sprintf, that it's
+ *    used at most the amount of space we had available.
+ * 
+ *  - Fault any formatting directive we don't fully understand. The
+ *    aim here is to _guarantee_ that we never overflow the buffer,
+ *    because this is a security-critical function. If we see a
+ *    directive we don't know about, we should panic and die rather
+ *    than run any risk.
  */
 char *dupprintf(const char *fmt, ...)
 {
@@ -181,6 +219,8 @@ void bufchain_add(bufchain *ch, const void *data, int len)
 {
     const char *buf = (const char *)data;
 
+    if (len == 0) return;
+
     ch->buffersize += len;
 
     if (ch->tail && ch->tail->buflen < BUFFER_GRANULE) {
@@ -293,14 +333,21 @@ void mlog(char *file, int line)
 }
 #endif
 
-void *safemalloc(size_t size)
+void *safemalloc(size_t n, size_t size)
 {
     void *p;
+
+    if (n > INT_MAX / size) {
+	p = NULL;
+    } else {
+	size *= n;
 #ifdef MINEFIELD
-    p = minefield_c_malloc(size);
+	p = minefield_c_malloc(size);
 #else
-    p = malloc(size);
+	p = malloc(size);
 #endif
+    }
+
     if (!p) {
 	char str[200];
 #ifdef MALLOC_LOG
@@ -320,22 +367,29 @@ void *safemalloc(size_t size)
     return p;
 }
 
-void *saferealloc(void *ptr, size_t size)
+void *saferealloc(void *ptr, size_t n, size_t size)
 {
     void *p;
-    if (!ptr) {
+
+    if (n > INT_MAX / size) {
+	p = NULL;
+    } else {
+	size *= n;
+	if (!ptr) {
 #ifdef MINEFIELD
-	p = minefield_c_malloc(size);
+	    p = minefield_c_malloc(size);
 #else
-	p = malloc(size);
+	    p = malloc(size);
 #endif
-    } else {
+	} else {
 #ifdef MINEFIELD
-	p = minefield_c_realloc(ptr, size);
+	    p = minefield_c_realloc(ptr, size);
 #else
-	p = realloc(ptr, size);
+	    p = realloc(ptr, size);
 #endif
+	}
     }
+
     if (!p) {
 	char str[200];
 #ifdef MALLOC_LOG