[PATCH] cp -p doesn't work with HAVE_FUTIMENS and without /proc

[Kir Kolyshkin]

I have come across a bug in cp utility from coreutils-5.93 on a Fedora 
Core 5 system (glibc-2.4), while working on OpenVZ user-level tools.

Original, unpatched versions of coreutils-5.93 and 5.94 are also affected.


PREREQUISITES
-------------
Bug occurs when coreutils is compiled on a system which provides 
futimens() function, and only if /proc fs is not mounted.


SYMPTOMS
--------
Copying a file with -p (or --preserve=timestamps) option gives the 
following error message; cp when exits with 1:

> cp: preserving times for `dst-file-name': Function not implemented



ANALYSYS
--------
Strace shows that cp tries to call utimes on /proc/self/fd/4, it fails 
and cp bails out:

> open("dst-file-name", O_WRONLY|O_CREAT|O_LARGEFILE, 0100644) = 4
> fstat64(4, {st_mode=S_IFREG|0644, st_size=0, ...}) = 0
> fstat64(3, {st_mode=S_IFREG|0644, st_size=0, ...}) = 0
> read(3, "", 4096)                       = 0
> utimes("/proc/self/fd/4", {1145050934, 0}) = -1 ENOENT (No such file 
> or directory)
> fcntl(4, F_GETFD)                       = 0
> write(2, "cp: ", 4cp: )                     = 4
> write(2, "preserving times for `dst-file-n"..., 36preserving times for 
> `dst-file-name') = 36
> write(2, ": Function not implemented", 26: Function not implemented) = 26
> write(2, "\n", 1
> )                       = 1


Ltrace shows that cp calls futimens, which fails, and cp bails out:

> open64("dst-file-name", 513, 
> 00)                                                = 4
> __fxstat64(3, 4, 
> 0xffffc184)                                                    = 0
> __fxstat64(3, 3, 
> 0xffffc184)                                                    = 0
> getpagesize()                                                                   
> = 4096
> read(3, "", 
> 4096)                                                               = 0
> futimesat(4, 0, -24452, 0x8058a20, 
> 0xf7dbfb94)                                  = -1
> __errno_location()                                                              
> = 0xf7d6b690
> __errno_location()                                                              
> = 0xf7d6b690
> __ctype_get_mb_cur_max(0xf7db25b0, 0xc0b8fae, 0, 0x8048ab0, 
> 494452)             = 1
> dcgettext(0, 0x8055c2a, 5, 0x80588dc, 
> 0xf7d6b690)                               = 0x8055c2a
> dcgettext(0, 0x8055f38, 5, 0x80588dc, 
> 0x8055c2a)                                = 0x8055f38
> strlen("'")                                                                     
> = 1
> dcgettext(0, 0x80558c1, 5, 0, 
> 0)                                                = 0x80558c1
> __errno_location()                                                              
> = 0xf7d6b690
> error(0, 38, 0x80558c1, 0x8058b00, 0cp: preserving times for 
> `dst-file-name': Function not implemented
> )                                           = 0


CODE
----
The following piece of code from coreutils/lib/utimens.c sheds some light:

> # if HAVE_FUTIMESAT
>   return fd < 0 ? futimesat (AT_FDCWD, file, t) : futimesat (fd, NULL, t);
> # elif HAVE_FUTIMES
>   if (0 <= fd)
>     {
>       if (futimes (fd, t) == 0)
>         return 0;
>
>       /* Don't worry about trying to speed things up by returning right
>          away here.  glibc futimes can incorrectly fail with errno ==
>          ENOENT if /proc isn't mounted.  Also, Mandrake 10.0 in high
>          security mode doesn't allow ordinary users to read /proc/self, so
>          glibc futimes incorrectly fails with errno == EACCES.  If futimes
>          fails with errno == EIO, EPERM, or EROFS, it's probably safe to
>          fail right away, but these cases are rare enough that they're not
>          worth optimizing, and who knows what other messed-up systems are
>          out there?  So play it safe and fall back on the code below.  */
>     }
> # endif
> #endif
Apparently, there is a fallback path for futimes, but there is no such 
path for futimesat.


FIX
---
Attached is the patch that enables fallback path for futimesat().

--- coreutils-5.93/lib/utimens.c        2005-11-02 15:16:12.000000000 +0300
+++ coreutils-5.93-cp-p-fix/lib/utimens.c       2006-04-14 23:33:49.000000000 
+0400
@@ -92,7 +92,14 @@
     t = NULL;
 
 # if HAVE_FUTIMESAT
-  return fd < 0 ? futimesat (AT_FDCWD, file, t) : futimesat (fd, NULL, t);
+  if (fd < 0)
+    return futimesat (AT_FDCWD, file, t);
+  else if (futimesat (fd, NULL, t) == 0)
+    return 0;
+  /* If futimesat failed, the reason might be that /proc is not mounted
+     or it is otherwise inaccessible. In that case we use the fallback code
+     below. 
+  */
 # elif HAVE_FUTIMES
   if (0 <= fd)
     {
@@ -112,8 +119,6 @@
 # endif
 #endif
 
-#if ! HAVE_FUTIMESAT
-
   if (!file)
     {
 # if ! (HAVE_WORKING_UTIMES && HAVE_FUTIMES)
@@ -151,8 +156,6 @@
     return utime (file, ut);
   }
 # endif
-
-#endif
 }
 
 /* Set the access and modification time stamps of FILE to be