Hello, On Tue, Sep 24, 2013 at 11:42:56AM +0800, Chen Gang wrote: > Hmm... can user be permitted to call other system call (e.g. getgroups) > before call groups_alloc()? (may the user space already give check, but > for our kernel, we can not only depend on their checking).
I don't think so. > According to group_alloc() and setgroups() usage in kernel source code, > 'group_info' may be not set if kernel/process is running (although user > space may be sure "if kernel is running, 'group_info' must be set"). > > The below is the proof for "kernel itself can not be sure 'group_info' > must be set during kernel/process is running", please check, thanks. ... > The related conclusion: > > during kernel startup or process creation, kernel does not intend to set > 'group_info'. No, this is not a proof or any meaningful conclusion. This is just some random suspicions combined with supposedly related grep output. > In extern function groups_search (which also called by export function > in_group_p and in_egroup_p), it checks "if 'cred->group_info' is NULL". > > So "kernel/groups.c" have 9 extern/export/system-call functions, and > 4/9 notice about "if 'cred->group_info' is NULL" (e.g. groups_alloc, > groups_search, in_group_p, in_egroup_p). > > So for API self-consistency, all of extern/export/system-call functions > need notice about it. I'm afraid this isn't useful. If you want to change the code, you actually need to understand what's going on. "this seems weird to me" is a good starting point but you need to go way beyond that to actually make changes. Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
