On 4/6/2023 2:14 AM, Roberto Sassu wrote: > On 4/5/2023 11:07 PM, Casey Schaufler wrote: >> On 4/5/2023 1:49 PM, Paul Moore wrote: >>> On Wed, Apr 5, 2023 at 4:43 PM Casey Schaufler >>> <casey@xxxxxxxxxxxxxxxx> wrote: >>>> On 4/5/2023 12:59 PM, Paul Moore wrote: >>>>> On Wed, Apr 5, 2023 at 5:44 AM Roberto Sassu >>>>> <roberto.sassu@xxxxxxxxxxxxxxx> wrote: >>>>>> On 4/5/2023 4:08 AM, Casey Schaufler wrote: >>>>>>> On 4/4/2023 11:54 AM, Paul Moore wrote: >>>>>>>> On Fri, Mar 31, 2023 at 8:33 AM Roberto Sassu >>>>>>>> <roberto.sassu@xxxxxxxxxxxxxxx> wrote: >>>>> .. >>>>> >>>>>>>>> diff --git a/security/smack/smack_lsm.c >>>>>>>>> b/security/smack/smack_lsm.c >>>>>>>>> index cfcbb748da2..8392983334b 100644 >>>>>>>>> --- a/security/smack/smack_lsm.c >>>>>>>>> +++ b/security/smack/smack_lsm.c >>>>>>>>> @@ -52,6 +52,15 @@ >>>>>>>>> #define SMK_RECEIVING 1 >>>>>>>>> #define SMK_SENDING 2 >>>>>>>>> >>>>>>>>> +/* >>>>>>>>> + * Smack uses multiple xattrs. >>>>>>>>> + * SMACK64 - for access control, SMACK64EXEC - label for the >>>>>>>>> program, >>>>>>>> I think it would be good to move SMACK64EXEC to its own line; >>>>>>>> it took >>>>>>>> me a minute to figure out why SMACK_INODE_INIT_XATTRS was set >>>>>>>> to '4' >>>>>>>> when I only say three comment lines ... ;) >>>>>>>> >>>>>>>>> + * SMACK64MMAP - controls library loading, >>>>>>>>> + * SMACK64TRANSMUTE - label initialization, >>>>>>>>> + * Not saved on files - SMACK64IPIN and SMACK64IPOUT >>>>>>>>> + */ >>>>>>>>> +#define SMACK_INODE_INIT_XATTRS 4 >>>>>>>> If smack_inode_init_security() only ever populates a single >>>>>>>> xattr, and >>>>>>>> that is the only current user of SMACK_INODE_INIT_XATTRS, can >>>>>>>> we make >>>>>>>> this '1' and shrink the xattr allocation a bit? >>>>>>> If the parent directory is marked with SMACK64_TRANSMUTE, the >>>>>>> access >>>>>>> rule allowing the access has the "t" mode, and the object being >>>>>>> initialized >>>>>>> is a directory, the new inode should get the SMACK64_TRANSMUTE >>>>>>> attribute. >>>>>>> The callers of security_inode_init_security() don't seem to care. >>>>>>> I can't say if the evm code is getting SMACK64_TRANSMUTE or, for >>>>>>> that >>>>>>> matter, SMACK64_EXEC and SMACK64_MMAP, some other way. The older >>>>>>> system >>>>>>> allowed for multiple Smack xattrs, but I'm not clear on exactly >>>>>>> how. >>>>>> If you like to set an additional xattr, that would be possible now. >>>>>> Since we reserve multiple xattrs, we can call lsm_get_xattr_slot() >>>>>> another time and set SMACK64_TRANSMUTE. >>>>>> >>>>>> I think, if the kernel config has CONFIG_EVM_EXTRA_SMACK_XATTRS set, >>>>>> EVM would protect SMACK64_TRANSMUTE too. >>>>> Ooookay, but can someone explain to me how either the current, or >>>>> patched, smack_inode_init_security() function can return multiple >>>>> xattrs via the security_inode_init_security() LSM hook? >>>> It can't. >>> I didn't think so. >>> >>> To be really specific, that's what we're talking about with this >>> patch: the number of xattrs that smack_inode_init_security() can >>> return to the LSM hook (and EVM, and the caller ...). If it's only >>> ever going to be one, I think we can adjust the >>> 'SMACK_INODE_INIT_XATTRS' down to '1' and save ourselves some >>> allocation space. >> >> Does evm have an expectation that mumble_inode_init_security() is >> going to report all the relevant attributes? It has to be getting >> them somehow, which leads me to wonder if we might want to extend >> smack_inode_init_security() to do so. Even if we did, the maximum >> value would be '2', SMACK64 and SMACK64_TRANSMUTE. Now that would >> require a whole lot of work in the calling filesystems, as setting >> the transmute attribute would be moving out of smack_d_instantiate() >> and into the callers. Or something like that. > > After changing the inode_init_security hook definition to pass the > full xattr array, this is not going to be a problem. EVM sees all > xattrs that are going to be set when an inode is created, and adds its > own too. > > If you have enough information to set security.SMACK_TRANSMUTE64 in > smack_inode_init_security(), I think there's enough information to do that. I'm going to have to look at your patch more closely. > this patch sets already allows to set both xattrs at the same time. We > would just need to call lsm_get_xattr_slot() another time, assuming > that we reserve two xattrs. > > Roberto >
