[vdr] trouble with asprintf

Wolfgang Rohdewald wolfgang at rohdewald.de
Sun Feb 10 22:16:27 CET 2008


On Sonntag, 10. Februar 2008, Udo Richter wrote:
>  What special 
> handling does asprintf with utf8? Is there some example that causes the 
> trouble?
 
> Worst case I can imagine would be that there's an invalid 0 byte inside 
> an utf8 multibyte char

printf and family sometimes have to count characters, so I suppose they have
to scan UTF

I know from mysql and postgresql that they also scan every UTF string
passed from the client for illegal chars and abort the transaction if they
find any.


My problem code:

mgDb::Build_cddbid(const mgSQLString& artist) const
{
	char *s;
	asprintf(&s,"%ld-%.9s",random(),artist.original());

segfaults only if illegal utf8 chars appear in artist.original()

asprintf returns -1, so s is nothing that could be freed,
and this gives a nice backtrace:

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread -1319449712 (LWP 22989)]
0xb7bf57ea in free () from /lib/tls/i686/cmov/libc.so.6
(gdb) bt
#0  0xb7bf57ea in free () from /lib/tls/i686/cmov/libc.so.6
#1  0xb7986908 in mgDb::Build_cddbid (this=0x86ed8e8, artist=@0xb15aa698) at mg_db.c:1023

If I change %.9s to %s, everything is fine.

I cannot easily simplify that, if I try like this, it works:

char artist[50];
strcpy(artist,"Celine Dion");
artist[1]=0xe9;
asprintf(&buffer,"%ld-%.9s",random(),artist);
printf(buffer);
free(buffer);


-- 
Wolfgang



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