full-disclosure - readdir_r considered harmful

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Message-ID: <228939283.20051101141205@SECURITY.NNOV.RU>
Date: Tue Nov  1 11:12:13 2005
From: 3APA3A at SECURITY.NNOV.RU (3APA3A)
Subject: readdir_r considered harmful

Dear Ben Hutchings,


If  someone  uses pathconf to determine buffer size it's his own problem
and  he creates vulnerability by himself. You can list such applications
as vulnerable to race conditions.

Recommended (according to POSIX) way is to use NAME_MAX:

buf  =  (struct  dirent  *)malloc(  offsetof(struct  dirent,  d_name)  +
NAME_MAX + 1))

See: The GNU C Library Reference Manual Chapter 14

and also POSIX standard itself says:

     The  storage pointed to by entry shall be large enough for a dirent
     with   an   array  of  char  d_name  members  containing  at  least
     {NAME_MAX}+1 elements.

See:
http://www.opengroup.org/onlinepubs/009695399/functions/readdir.html
     
NAME_MAX  is  defined  in limits.h and should be 255 according to latest
POSIX extension. I see no problem with POSIX standard in this case.

See:
http://www.opengroup.org/onlinepubs/009695399/basedefs/limits.h.html
     
--Tuesday, November 1, 2005, 6:57:03 AM, you wrote to bugtraq@...urityfocus.com:

BH> readdir_r considered harmful
BH> ============================


BH>         if ((dir = opendir(argv[1]))
BH>             && (name_max = pathconf(argv[1], _PC_NAME_MAX)) > 0
BH>             && (buf = (struct dirent *)malloc(
BH>                     offsetof(struct dirent, d_name) + name_max + 1))

-- 
~/ZARAZA
http://www.security.nnov.ru/