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. -- paul-moore.com
