1) Ok, i found why this function is dangerous. https://buildsecurityin.us-cert.gov/bsi/articles/knowledge/coding/760-BSI.html "Since the user cannot specify the length of the buffer passed to getwd(), use of this function is discouraged. The length of a pathname described in {PATH_MAX} is file system-dependent and may vary from one mount point to another, or might even be unlimited. It is possible to overflow this buffer in such a way as to cause applications to fail or possible system security violations."
But here i make a test no real life project. 2) So, i found in /usr/include/linux/limits.h Line Number: 12 #define PATH_MAX 4096 /* # chars in a path name including nul */ is this the value? i tried this value in my example with no success, i make somewhere else the mistake. --------------- ' Gambas module file ' Gambas module file 'char *getwd(char *buf); Extern getwd(buf As Pointer) As Pointer In "libc:6" Public Sub Main() Dim pBuf As Pointer Dim pFunc As Pointer Dim sWorkingDirectory As String 'getwd pBuf = Alloc(4096) pFunc = Alloc(4096) pFunc = getwd(pBuf) sWorkingDirectory = Str@(pFunc) Free(pFunc) Free(pBuf) Print sWorkingDirectory End --------------- signal #6 ---------------- *** glibc detected *** Pointers5: double free or corruption (!prev): 0x0893f498 *** ======= Backtrace: ========= /lib/tls/i686/cmov/libc.so.6(+0x6b591)[0x17b591] /lib/tls/i686/cmov/libc.so.6(+0x6cde8)[0x17cde8] /lib/tls/i686/cmov/libc.so.6(cfree+0x6d)[0x17fecd] Pointers5[0x805ed2e] Pointers5[0x8076a6a] Pointers5[0x8050a99] Pointers5[0x80513d8] Pointers5[0x80689cd] /lib/tls/i686/cmov/libc.so.6(__libc_start_main+0xe6)[0x126bd6] Pointers5[0x804b151] ======= Memory map: ======== 00110000-00263000 r-xp 00000000 08:04 2019753 /lib/tls/i686/cmov/libc-2.11.1.so 00263000-00264000 ---p 00153000 08:04 2019753 /lib/tls/i686/cmov/libc-2.11.1.so 00264000-00266000 r--p 00153000 08:04 2019753 /lib/tls/i686/cmov/libc-2.11.1.so 00266000-00267000 rw-p 00155000 08:04 2019753 /lib/tls/i686/cmov/libc-2.11.1.so 00267000-0026a000 rw-p 00000000 00:00 0 00428000-00438000 r-xp 00000000 08:04 1906544 /usr/local/lib/gambas3/gb.eval.so.0.0.0 00438000-00439000 r--p 0000f000 08:04 1906544 /usr/local/lib/gambas3/gb.eval.so.0.0.0 00439000-0043b000 rw-p 00010000 08:04 1906544 /usr/local/lib/gambas3/gb.eval.so.0.0.0 0043b000-0043c000 rw-p 00000000 00:00 0 0046e000-0046f000 r-xp 00000000 00:00 0 [vdso] 006c9000-006ce000 r-xp 00000000 08:04 688690 /usr/lib/libffi.so.5.0.10 006ce000-006cf000 ---p 00005000 08:04 688690 /usr/lib/libffi.so.5.0.10 006cf000-006d0000 r--p 00005000 08:04 688690 /usr/lib/libffi.so.5.0.10 006d0000-006d1000 rw-p 00006000 08:04 688690 /usr/lib/libffi.so.5.0.10 00739000-0075d000 r-xp 00000000 08:04 2019761 /lib/tls/i686/cmov/libm-2.11.1.so 0075d000-0075e000 r--p 00023000 08:04 2019761 /lib/tls/i686/cmov/libm-2.11.1.so 0075e000-0075f000 rw-p 00024000 08:04 2019761 /lib/tls/i686/cmov/libm-2.11.1.so 00aa5000-00ac2000 r-xp 00000000 08:04 1995027 /lib/libgcc_s.so.1 00ac2000-00ac3000 r--p 0001c000 08:04 1995027 /lib/libgcc_s.so.1 00ac3000-00ac4000 rw-p 0001d000 08:04 1995027 /lib/libgcc_s.so.1 00bca000-00bcc000 r-xp 00000000 08:04 2019759 /lib/tls/i686/cmov/libdl-2.11.1.so 00bcc000-00bcd000 r--p 00001000 08:04 2019759 /lib/tls/i686/cmov/libdl-2.11.1.so 00bcd000-00bce000 rw-p 00002000 08:04 2019759 /lib/tls/i686/cmov/libdl-2.11.1.so 00c25000-00c3a000 r-xp 00000000 08:04 2019772 /lib/tls/i686/cmov/libpthread-2.11.1.so 00c3a000-00c3b000 r--p 00014000 08:04 2019772 /lib/tls/i686/cmov/libpthread-2.11.1.so 00c3b000-00c3c000 rw-p 00015000 08:04 2019772 /lib/tls/i686/cmov/libpthread-2.11.1.so 00c3c000-00c3e000 rw-p 00000000 00:00 0 00dc3000-00dc7000 r-xp 00000000 08:04 1906676 /usr/local/lib/gambas3/gb.debug.so.0.0.0 00dc7000-00dc8000 r--p 00003000 08:04 1906676 /usr/local/lib/gambas3/gb.debug.so.0.0.0 00dc8000-00dc9000 rw-p 00004000 08:04 1906676 /usr/local/lib/gambas3/gb.debug.so.0.0.0 00eeb000-00f06000 r-xp 00000000 08:04 1996732 /lib/ld-2.11.1.so 00f06000-00f07000 r--p 0001a000 08:04 1996732 /lib/ld-2.11.1.so 00f07000-00f08000 rw-p 0001b000 08:04 1996732 /lib/ld-2.11.1.so 08048000-0807e000 r-xp 00000000 08:04 1785292 /usr/local/bin/gbx3 0807e000-0807f000 r--p 00035000 08:04 1785292 /usr/local/bin/gbx3 0807f000-08084000 rw-p 00036000 08:04 1785292 /usr/local/bin/gbx3 08084000-08086000 rw-p 00000000 00:00 0 08932000-08953000 rw-p 00000000 00:00 0 [heap] b7500000-b7521000 rw-p 00000000 00:00 0 b7521000-b7600000 ---p 00000000 00:00 0 b768a000-b76c9000 r--p 00000000 08:04 737484 /usr/lib/locale/en_US.utf8/LC_CTYPE b76c9000-b77e7000 r--p 00000000 08:04 737483 /usr/lib/locale/en_US.utf8/LC_COLLATE b77e7000-b77e9000 rw-p 00000000 00:00 0 b77f1000-b77f2000 r--p 00000000 08:04 737500 /usr/lib/locale/en_US.utf8/LC_NUMERIC b77f2000-b77f3000 r--p 00000000 08:04 735917 /usr/lib/locale/en_US.utf8/LC_TIME b77f3000-b77f4000 r--p 00000000 08:04 735918 /usr/lib/locale/en_US.utf8/LC_MONETARY b77f4000-b77f5000 r--p 00000000 08:04 752258 /usr/lib/locale/en_US.utf8/LC_MESSAGES/SYS_LC_MESSAGES b77f5000-b77f6000 r--p 00000000 08:04 737523 /usr/lib/locale/en_US.utf8/LC_PAPER b77f6000-b77f7000 r--p 00000000 08:04 737455 /usr/lib/locale/en_US.utf8/LC_NAME b77f7000-b77f8000 r--p 00000000 08:04 735919 /usr/lib/locale/en_US.utf8/LC_ADDRESS b77f8000-b77f9000 r--p 00000000 08:04 735920 /usr/lib/locale/en_US.utf8/LC_TELEPHONE b77f9000-b77fa000 r--p 00000000 08:04 737398 /usr/lib/locale/en_US.utf8/LC_MEASUREMENT b77fa000-b7801000 r--s 00000000 08:04 1619066 /usr/lib/gconv/gconv-modules.cache b7801000-b7802000 r--p 00000000 08:04 735921 /usr/lib/locale/en_US.utf8/LC_IDENTIFICATION b7802000-b7806000 rw-p 00000000 00:00 0 bfa53000-bfa68000 rw-p 00000000 00:00 0 [stack] ---------------- i saw that the first line says *** glibc detected *** Pointers5: double free or corruption (!prev) and i rem the one Free(). now i get -------------- gbx3: warning: 1 allocation(s) non freed. ���...@^@^...@^@^...@^@^...@^@^...@ocuments/Development/Gambas3/Pointers5 -------------- but no crash. i played with the values of Alloc and i found that in my case a 29 bytes are ok but with one Free() or else i get signal #11. is there a bug with Free(pBuf) Free(pFunc) ? 3) On the other hand, i have a general question. How to deal with char *pointers when their length is not known? 4) For example i try to use 'char *get_current_dir_name(void); Extern get_current_dir_name() As Pointer In "libc:6" again with no success. in manuall says: get_current_dir_name() will malloc(3) an array big enough to hold the absolute pathname of the current working directory. in my example: --------------------- ' Gambas module file 'char *get_current_dir_name(void); Extern get_current_dir_name() As Pointer In "libc:6" Public Sub Main() Dim pFunc As Pointer Dim sWorkingDirectory As String 'get_current_dir_name pFunc = Alloc(4096) pFunc = get_current_dir_name() sWorkingDirectory = Str@(pFunc) ' Free(pFunc) Print sWorkingDirectory End --------------------- if i use Free(pFunc) i get signal #11 gambas3-svn3418, ubuntu 10.04 On Sun, 2011-01-09 at 21:37 +0100, Benoît Minisini wrote: > > so what can i do for > > > > char *getwd(char *buf); > > > > ? > > > > You must know C programming first, and understand how getwd works. By typing > 'man getwd', you will learn that you must not use that function, it is > dangerous and so deprecated. > > Then you will read that buf must be a pointer to a memory allocation of > PATH_MAX bytes. You must find the value of this constant inside the standard > C > header files. > > SizeOf(gb.String) is 4 (on 32 bits system). It is the number of bytes used by > Gambas to store a pointer to a Gambas string. This is the reason why you get > a > crash. > > Regards, > -- Regards, Demosthenes ------------------------------------------------------------------------------ Gaining the trust of online customers is vital for the success of any company that requires sensitive data to be transmitted over the Web. 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