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.
