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From Bob Galloway <...@tripod.com>
Subject apache-api/2941: ap_log_printf interprets constructed string as printf format string, not literal
Date Tue, 01 Sep 1998 21:31:51 GMT

>Number:         2941
>Category:       apache-api
>Synopsis:       ap_log_printf interprets constructed string as printf format string, not
literal
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    apache
>State:          open
>Class:          sw-bug
>Submitter-Id:   apache
>Arrival-Date:   Tue Sep  1 14:40:01 PDT 1998
>Last-Modified:
>Originator:     bob@tripod.com
>Organization:
apache
>Release:        1.3.1
>Environment:
Solaris 2.5.1, Linux 2.x
>Description:
ap_log_printf calls ap_log_error to print the expanded string.  
ap_log_error treats that processed string as a printf-style format, 
not a literal.  


API_EXPORT(void) ap_log_error (const char *file, int line, int level,
                              const server_rec *s, const char *fmt, ...);

API_EXPORT(void) ap_log_printf (const server_rec *s, const char *fmt, ...)
{
    char buf[MAX_STRING_LEN];
    va_list args;
    
    va_start(args, fmt);
    ap_vsnprintf(buf, sizeof(buf), fmt, args);   /* construct buffer from varargs */
    ap_log_error(APLOG_MARK, APLOG_ERR, s, buf); /* use buffer as format, not literal */
    va_end(args);
}


This will cause ap_log_error_old and ap_log_unixerr to barf, too,
if the string contains %.
>How-To-Repeat:
One example:

int tripod_auth_fixups(request_rec *r) {
  /* testing */
  ap_log_printf(r->server, "a string: \"%s\"\n", "a string with %s escapes");
  /*  ap_log_error_old("a string with %s escapes",r->server); */
  /*  ap_log_unixerr("a routine","a file","a string with %s escapes",r->server); */
}

running the server under gdb gives:

Program received signal SIGSEGV, Segmentation fault.
0xef5a3e74 in strlen ()
(gdb) bt
#0  0xef5a3e74 in strlen ()
#1  0x72094 in ap_vformatter (flush_func=0x72acc <snprintf_flush>, vbuff=0xefffb508,
fmt=0xefffd632 "s escapes\"\n", 
    ap=0xefffd60c) at ap_snprintf.c:766
#2  0x72c0c in ap_vsnprintf (buf=0xefffb5d9 "a string: \"a string with ", len=8127, 
    format=0xefffd618 "a string: \"a string with %s escapes\"\n", ap=0xefffd608) at ap_snprintf.c:1022
#3  0x52ab8 in ap_log_error (file=0x89aa8 "http_log.c", line=453, level=3, s=0xd34a0, 
    fmt=0xefffd618 "a string: \"a string with %s escapes\"\n") at http_log.c:403
#4  0x52d4c in ap_log_printf (s=0xd34a0, fmt=0x80ac8 "a string: \"%s\"\n") at http_log.c:453
#5  0x25dfc in tripod_auth_fixups (r=0xecc68) at mod_auth_tripod.c:499
#6  0x47d9c in run_method (r=0xecc68, offset=21, run_all=1) at http_config.c:357
#7  0x47f10 in ap_run_fixups (r=0xecc68) at http_config.c:384
#8  0x61d20 in process_request_internal (r=0xecc68) at http_request.c:1207
#9  0x61dc4 in ap_process_request (r=0xecc68) at http_request.c:1229
#10 0x571f4 in child_main (child_num_arg=2) at http_main.c:3638
#11 0x57534 in make_child (s=0xc2d40, slot=2, now=904684385) at http_main.c:3758
#12 0x5764c in startup_children (number_to_start=18) at http_main.c:3785
#13 0x57f28 in standalone_main (argc=3, argv=0xeffffba4) at http_main.c:4063
#14 0x58980 in main (argc=3, argv=0xeffffba4) at http_main.c:4336

>Fix:
ap_log_printf calls ap_log_error to print the processed string.  
ap_log_error treats the processed string as a printf-style format, 
not a literal.  If ap_log_printf (and the other ap_log_* functions 
that take a string literal) called a log-error function
that prints an unmolested string literal, the problem would be solved.
>Audit-Trail:
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