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Fix buffer management in strbuf_catfv.

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Thanks to Tim Kosse for pointing out that I had _completely_ cocked up
all the code that was supposed to enlarge the buffer in the strbuf
structure, by failing to pass in 'oldsize' to the innermost
dupvprintf_inner function by reference, so that the size was never
updated.

Fortunately, this whole mechanism was something I dashed off for the
purposes of buildinfo(), which means it's only ever used to glue
together a fixed number of compile-time string constants, for which
there turns out to be plenty to spare in the standard 512 bytes
allocated to a new strbuf. So it's at least not dangerous, though it
clearly needs to be fixed before I make the mistake of using
strbuf_catf[v] for anything else!
This commit is contained in:
Simon Tatham 2017-02-20 20:30:14 +00:00
parent bd65d47792
commit 7705fc4470
1 changed files with 14 additions and 7 deletions
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21
misc.c
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@ -394,15 +394,19 @@ int toint(unsigned u)
* directive we don't know about, we should panic and die rather
* than run any risk.
*/
static char *dupvprintf_inner(char *buf, int oldlen, int oldsize,
static char *dupvprintf_inner(char *buf, int oldlen, int *oldsize,
const char *fmt, va_list ap)
{
int len, size;
int len, size, newsize;
size = oldsize - oldlen;
assert(*oldsize >= oldlen);
size = *oldsize - oldlen;
if (size == 0) {
size = 512;
buf = sresize(buf, oldlen + size, char);
newsize = oldlen + size;
buf = sresize(buf, newsize, char);
} else {
newsize = *oldsize;
}
while (1) {
@ -430,6 +434,7 @@ static char *dupvprintf_inner(char *buf, int oldlen, int oldsize,
if (len >= 0 && len < size) {
/* This is the C99-specified criterion for snprintf to have
* been completely successful. */
*oldsize = newsize;
return buf;
} else if (len > 0) {
/* This is the C99 error condition: the returned length is
@ -440,13 +445,15 @@ static char *dupvprintf_inner(char *buf, int oldlen, int oldsize,
* buffer wasn't big enough, so we enlarge it a bit and hope. */
size += 512;
}
buf = sresize(buf, oldlen + size, char);
newsize = oldlen + size;
buf = sresize(buf, newsize, char);
}
}
char *dupvprintf(const char *fmt, va_list ap)
{
return dupvprintf_inner(NULL, 0, 0, fmt, ap);
int size = 0;
return dupvprintf_inner(NULL, 0, &size, fmt, ap);
}
char *dupprintf(const char *fmt, ...)
{
@ -488,7 +495,7 @@ char *strbuf_to_str(strbuf *buf)
}
void strbuf_catfv(strbuf *buf, const char *fmt, va_list ap)
{
buf->s = dupvprintf_inner(buf->s, buf->len, buf->size, fmt, ap);
buf->s = dupvprintf_inner(buf->s, buf->len, &buf->size, fmt, ap);
buf->len += strlen(buf->s + buf->len);
}
void strbuf_catf(strbuf *buf, const char *fmt, ...)