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SubjectRe: User limit
On Thu, May 06, 1999 at 06:37:53AM +0000, Martin Neumann wrote:
> > I'm trying to create more than 64K user accounts on a Linux Intel box, but i
> > already know that it can't be done, so my only hope right now is that Alpha
> > or Sparc Linux does support more than 64K users... is that true?
>
> That would have been easy to find out - you've got the source ..
>
> % find ./ -name '*.h'|xargs grep kernel_uid_t
> ./include/linux/types.h:typedef __kernel_uid_t uid_t;
> ./include/asm-i386/posix_types.h:typedef unsigned short __kernel_uid_t;
> ./include/asm-mips/posix_types.h:typedef long __kernel_uid_t;
> ./include/asm-alpha/posix_types.h:typedef unsigned int __kernel_uid_t;
> ./include/asm-m68k/posix_types.h:typedef unsigned short __kernel_uid_t;
> ./include/asm-sparc/posix_types.h:typedef unsigned short __kernel_uid_t;
> ./include/asm-ppc/posix_types.h:typedef unsigned int __kernel_uid_t;
> ./include/asm-sparc64/posix_types.h:typedef unsigned int __kernel_uid_t;
> ./include/asm-sparc64/posix_types.h:typedef unsigned short __kernel_uid_t32;
> ./include/asm-arm/posix_types.h:typedef unsigned short __kernel_uid_t;
>
> >From my understanding, mips, alpha, ppc and sparc64 should have UIDs > 2^16

That's only half the story. Ext2 doesn't store the high 16-bit of the UID
and GID in the disk inode. In some cases of braindead software this may
even result in very hideous problems since both are equivalent modulo 65536,
that is for example UIDs 0, 65536 and 131072 are equivalent. Security fun
ahead.

Ralf

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