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Description of problem:
Apparently there is an off-by-one error in the listxattr() system call support, that leads to spurious ERANGE errors.  See for instance this strace output:

listxattr("/dev", (nil), 0)             = 17
listxattr("/dev", 0x53a3d0, 17)         = -1 ERANGE (Numerical result out of range)

when since the previous listxattr call returned 17, the buffer in the second case should be sufficient.  For more information and fix see:

http://bugzilla.kernel.org/show_bug.cgi?id=5745

Note that the included getfattr utility does not trigger this bug because that utility uses a buffer bigger than it should.

Version-Release number of selected component (if applicable):
kernel-2.6.14-1.1644_FC4, other 2.6.14 kernel versions

How reproducible:
Always

Steps to Reproduce:
1. See the attached small C program, written by Iustin Pop
2. Run it on /dev for instance, or /proc

Actual Results:  Path /dev, xattr size 17
Testing with size 16...buffer too small
Testing with size 17...buffer too small
Testing with size 18... succeded!
Finished at 18


Expected Results:  Path /dev, xattr size 17
Testing with size 16...buffer too small
Testing with size 17... succeded!
Finished at 17

Additional info:

Here's Iustin Pop's C program:

#include <sys/types.h>
#include <attr/xattr.h>
#include <string.h>
#include <stdio.h>

int main(int argc, char *argv[]) {
   char buf[65536];

   ssize_t n;
   ssize_t i;
   ssize_t j;
   char *path;

   if(argc != 2) {
       fprintf(stderr, "Usage: %s path\n", argv[0]);
       return 1;
   }
   path = argv[1];
   n = listxattr(path, NULL, 0);

   if(n == -1) {
       fprintf(stderr, "Error in getting xattr list size: %s", strerror(errno));
       return 1;
   }
   printf("Path %s, xattr size %d\n", path, n);

   if(n == 0) {
       printf("No extended attrs, exiting.\n");
       return 0;
   }

   for(i = n - 1; i < sizeof(buf); i++) {
       printf("Testing with size %d...", i);
       j = listxattr(path, buf, i);
       if(j > 0) {
           printf(" succeded!\n");
           break;
       }
       if(errno == ERANGE) {
           printf("buffer too small\n");
       } else {
           printf("other error: %s\n", strerror(errno));
       } 
   }
   printf("Finished at %d\n", i);
   return 0;
}