On Wed, May 05, 2004 at 12:28:34PM +1000, John Newbigin wrote:
> Here is a more complete check procedure.
Yes, a check of all path components is preferable.
> I have used this code so I hope it is secure :)
Unfortunately, no.
> if(buf.st_uid != 0)
> {
> // make sure there is no user write access
> if(buf.st_mode & S_IWUSR)
> {
> result = -1;
> fprintf(stderr, "non root user
> has write access to %s\n", name);
> }
> }
If a non-root user owns a directory, the user should be assumed to
have write access to it. You must not check for S_IWUSR, that is
largely irrelevant. This is because the user can chmod a directory
he owns after your check has run.
> if(buf.st_gid != 0)
> {
> // make sure there is no group write access
> if(buf.st_mode & S_IWGRP)
> {
> result = -1;
> fprintf(stderr, "non root group
> has write access to %s\n", name);
> }
> }
And this check is buggy in "the opposite" way: you must not check for
GID 0 because it is not special to the kernel in any way and generally
there's no valid reason to consider it trusted.
> // make sure there is no group write access
> if(buf.st_mode & S_IWOTH)
> {
> result = -1;
> fprintf(stderr, "all users have write
> access to %s\n", name);
> }
This one is OK, but I suggest that you combine it with the S_IWGRP
check above to simplify the code. I don't see much need to have
different error messages for the three cases.
--
Alexander Peslyak <solar@xxxxxxxxxxxx>
GPG key ID: B35D3598 fp: 6429 0D7E F130 C13E C929 6447 73C3 A290 B35D 3598
http://www.openwall.com - bringing security into open computing environments
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