Date: Fri, 11 Oct 2013 16:19:09 +1100 From: Ryan Mallon <rmallon@...il.com> To: George Spelvin <linux@...izon.com>, 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, viro@...iv.linux.org.uk Subject: Re: [PATCH v3a] vsprintf: Check real user/group id for %pK On 11/10/13 15:42, George Spelvin wrote: > 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.) Yeah, that is probably the best solution. I'll try to put together a patch series doing this. It will obviously be more involved though, so I think it is still worth merging the original patch in the interm. ~Ryan
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