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'm hoping > I'm missing something really obvious, but I can only see a single > Smack xattr being returned ... Smack is setting the transmute attribute in smack_d_instantiate(). The exec and mmap attributes are always set explicitly. I don't know how the "extra" Smack attributes were obtained by evm before, and I haven't been looking at how they're doing it now. I have assumed that CONFIG_EVM_EXTRA_SMACK_XATTRS does something meaningful.
