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Fix buffer overflow vulnerability in format() #26

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Fix buffer overflow vulnerability in format() #26

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31 changes: 20 additions & 11 deletions ddate.c
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Original file line number Diff line number Diff line change
Expand Up @@ -162,7 +162,7 @@ static char *sel(char **strings, int num) {
return(strings[rand()%num]);
}

void format(char *buf, const char* fmt, struct disc_time dt);
void format(char *buf, size_t bufsize, const char* fmt, struct disc_time dt);

struct disc_time convert(int,int);
struct disc_time makeday(int,int,int);
Expand Down Expand Up @@ -223,17 +223,18 @@ main (int argc, char *argv[]) {
hastur=convert(bob,raw);
fnord=fnord?fnord:default_immediate_fmt;
}
format(schwa, fnord, hastur);
format(schwa, sizeof(schwa), fnord, hastur);
printf("%s\n", schwa);

return 0;
}

void format(char *buf, const char* fmt, struct disc_time dt)
void format(char *buf, size_t bufsize, const char* fmt, struct disc_time dt)
{
int tib_start=-1, tib_end=0;
int i, fmtlen=strlen(fmt);
char *bufptr=buf;
char *bufend=buf + bufsize - 1; /* leave room for null terminator */

/* fprintf(stderr, "format(%p, \"%s\", dt)\n", buf, fmt);*/

Expand All @@ -257,11 +258,15 @@ void format(char *buf, const char* fmt, struct disc_time dt)
/* now do the formatting */
buf[0]=0;

for(i=0; i<fmtlen; i++) {
for(i=0; i<fmtlen && bufptr < bufend; i++) {
if((i==tib_start) && (dt.day==-1)) {
/* handle St. Tib's Day */
strcpy(bufptr, ("St. Tib's Day"));
bufptr += strlen(bufptr);
const char *tibs = "St. Tib's Day";
size_t len = strlen(tibs);
size_t avail = bufend - bufptr;
if(len > avail) len = avail;
memcpy(bufptr, tibs, len);
bufptr += len;
i=tib_end;
} else {
if(fmt[i]=='%') {
Expand All @@ -271,27 +276,31 @@ void format(char *buf, const char* fmt, struct disc_time dt)
case 'a': wibble=day_short[dt.yday%5]; break;
case 'B': wibble=season_long[dt.season]; break;
case 'b': wibble=season_short[dt.season]; break;
case 'd': sprintf(snarf, "%d", dt.day+1); wibble=snarf; break;
case 'e': sprintf(snarf, "%d%s", dt.day+1, ending(dt.day+1));
case 'd': snprintf(snarf, sizeof(snarf), "%d", dt.day+1); wibble=snarf; break;
case 'e': snprintf(snarf, sizeof(snarf), "%d%s", dt.day+1, ending(dt.day+1));
wibble=snarf; break;
case 'H': if(dt.day==4||dt.day==49)
wibble=holyday[dt.season][dt.day==49]; break;
case 'N': if(dt.day!=4&&dt.day!=49) goto eschaton; break;
case 'n': *(bufptr++)='\n'; break;
case 't': *(bufptr++)='\t'; break;

case 'Y': sprintf(snarf, "%d", dt.year); wibble=snarf; break;
case 'Y': snprintf(snarf, sizeof(snarf), "%d", dt.year); wibble=snarf; break;
case '.': wibble=sel(excl, ARRAY_SIZE(excl));
break;
#ifdef KILL_BOB
case 'X': sprintf(snarf, "%d",
case 'X': snprintf(snarf, sizeof(snarf), "%d",
xday_countdown(dt.yday, dt.year));
wibble = snarf; break;
#endif /* KILL_BOB */
}
if(wibble) {
/* fprintf(stderr, "wibble = (%s)\n", wibble);*/
strcpy(bufptr, wibble); bufptr+=strlen(wibble);
size_t len = strlen(wibble);
size_t avail = bufend - bufptr;
if(len > avail) len = avail;
memcpy(bufptr, wibble, len);
bufptr += len;
}
} else {
*(bufptr++) = fmt[i];
Expand Down