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Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: <2dc7318d6c74b27a49b4c64b513f3da13d980473.camel@HansenPartnership.com> References: <2dc7318d6c74b27a49b4c64b513f3da13d980473.camel@HansenPartnership.com> <462886.1749731810@warthog.procyon.org.uk> To: James Bottomley Cc: dhowells@redhat.com, keyrings@vger.kernel.org, Jarkko Sakkinen , Steve French , Chuck Lever , Mimi Zohar , Paulo Alcantara , Herbert Xu , Jeffrey Altman , hch@infradead.org, linux-afs@lists.infradead.org, linux-nfs@vger.kernel.org, linux-cifs@vger.kernel.org, linux-security-module@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-crypto@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC] Keyrings: How to make them more useful Precedence: bulk X-Mailing-List: linux-crypto@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <473710.1749760578.1@warthog.procyon.org.uk> Date: Thu, 12 Jun 2025 21:36:18 +0100 Message-ID: <473711.1749760578@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 3.0 on 10.30.177.15 James Bottomley wrote: > One of the problems I keep tripping over is different special casing > for user keyrings (which are real struct key structures) and system > keyrings which are special values of the pointer in struct key *. It's meant to be like that. The trusted system keyrings are static within system_keyring.c and not so easily accessible by kernel modules for direct modification, bypassing the security checks. Obviously this is merely a bit of obscurity and enforcement isn't possible against kernel code that is determined to modify those keyrings or otherwise interfere in the verification process. > For examples of what this special handling does, just look at things > like bpf_trace.c:bpf_lookup_{user|system}_key > > Since the serial allocation code has a hard coded not less than 3 > (which looks for all the world like it was designed to mean the two > system keyring id's were never used as user serial numbers) That's just a coincidence. The <3 thing predates the advent of those system keyring magic pointers. > I think we could simply allow the two system keyring ids to be passed into > lookup_user_key() (which now might be a bit misnamed) and special case not > freeing it in put_key(). If you want to make lookup_user_key() provide access to specific keyrings like this, just use the next negative numbers - it's not like we're likely to run out soon. But I'd rather not let lookup_user_key() return pointers to these keyrings... David