Date: 11 Oct 2013 00:42:32 -0400 From: "George Spelvin" <linux@...izon.com> To: ebiederm@...ssion.com, joe@...ches.com Cc: akpm@...ux-foundation.org, dan.j.rosenberg@...il.com, eldad@...refinery.com, jgunthorpe@...idianresearch.com, jkosina@...e.cz, keescook@...omium.org, kernel-hardening@...ts.openwall.com, linux-kernel@...r.kernel.org, linux@...izon.com, rmallon@...il.com, viro@...iv.linux.org.uk Subject: Re: [PATCH v3a] vsprintf: Check real user/group id for %pK ebiederm@...ssion.com (Eric W. Biederman) wrote: > Sigh. This is all wrong. The only correct thing to test is > file->f_cred. Aka the capabilities of the program that opened the > file. > > Which means that the interface to %pK in the case of kptr_restrict is > broken as it has no way to be passed the information it needs to make > a sensible decision. I looked at the code, and pretty painful. Certainly it's possible to include a reference to the file (I was thinking of just the credentials, actually) in the seq_file. But getting that to the vsprintf.c code (specifically, the pointer() function) is a PITA. I'm willing to accept the currently proposed kludge as a "good enough" approximation, as long as we're all agreed that using the credentials at open() time would be The Right Thing, and hopefully someone will find the round tuitts to implement that in future. But in the meantime, "the perfect is the enemey of the good" is worth remembering. (An alternate implementation I've been thinking about would be to do away with %pK, and instead have a "secret_ptr(p, seq->cred)" helper that returned p or 0 depending on the credential.)
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