Issue #767: Buffer overflow printing a filename

The safe_fprintf function attempts to ensure clean output for an
arbitrary sequence of bytes by doing a trial conversion of the
multibyte characters to wide characters -- if the resulting wide
character is printable then we pass through the corresponding bytes
unaltered, otherwise, we convert them to C-style ASCII escapes.

The stack trace in Issue #767 suggest that the 20-byte buffer
was getting overflowed trying to format a non-printable multibyte
character.  This should only happen if there is a valid multibyte
character of more than 5 bytes that was unprintable.  (Each byte
would get expanded to a four-charcter octal-style escape of the form
"\123" resulting in >20 characters for the >5 byte multibyte character.)

I've not been able to reproduce this, but have expanded the conversion
buffer to 128 bytes on the belief that no multibyte character set
has a single character of more than 32 bytes.

diff --git a/tar/util.c b/tar/util.c
index 9ff22f2b61546c18a078499b94698498473280c7..2b4aebe8e6079caad7609ca830530674c8f960db 100644 (file)
--- a/tar/util.c
+++ b/tar/util.c
@@ -182,7 +182,7 @@ safe_fprintf(FILE *f, const char *fmt, ...)
                }
 
                /* If our output buffer is full, dump it and keep going. */
-               if (i > (sizeof(outbuff) - 20)) {
+               if (i > (sizeof(outbuff) - 128)) {
                        outbuff[i] = '\0';
                        fprintf(f, "%s", outbuff);
                        i = 0;