Re: [PATCH v20 05/23] net: Prepare UDS for security module stacking

On 9/4/2020 1:08 PM, Paul Moore wrote: > On Wed, Aug 26, 2020 at 11:07 AM Casey Schaufler <casey(a)schaufler-ca.com&gt; wrote: >> Change the data used in UDS SO_PEERSEC processing from a >> secid to a more general struct lsmblob. Update the >> security_socket_getpeersec_dgram() interface to use the >> lsmblob. There is a small amount of scaffolding code >> that will come out when the security_secid_to_secctx() >> code is brought in line with the lsmblob. >> >> Signed-off-by: Casey Schaufler <casey(a)schaufler-ca.com&gt; >> --- >> include/linux/security.h | 7 +++++-- >> include/net/af_unix.h | 2 +- >> include/net/scm.h | 8 +++++--- >> net/ipv4/ip_sockglue.c | 8 +++++--- >> net/unix/af_unix.c | 6 +++--- >> security/security.c | 18 +++++++++++++++--- >> 6 files changed, 34 insertions(+), 15 deletions(-) > ... > >> diff --git a/include/net/af_unix.h b/include/net/af_unix.h >> index f42fdddecd41..a86da0cb5ec1 100644 >> --- a/include/net/af_unix.h >> +++ b/include/net/af_unix.h >> @@ -36,7 +36,7 @@ struct unix_skb_parms { >> kgid_t gid; >> struct scm_fp_list *fp; /* Passed files */ >> #ifdef CONFIG_SECURITY_NETWORK >> - u32 secid; /* Security ID */ >> + struct lsmblob lsmblob; /* Security LSM data */ > As mentioned in a previous revision, I remain concerned that this is > going to become a problem due to the size limit on unix_skb_parms. I > would need to redo the math to be certain, but if I recall correctly > this would limit us to five LSMs assuming both that we don't need to > grow the per-LSM size of lsmblob *and* the netdev folks don't decide > to add more fields to the unix_skb_parms. > > I lost track of that earlier discussion so I'm not sure where it ended > up, but if there is a viable alternative it might be a good idea to > pursue it. Stephen had concerns about the lifecycle management involved. He also pointed out that I had taken a cowards way out when allocations failed. That could result in unexpected behavior when an allocation failed. Fixing that would have required a major re-write of the currently simple UDS attribute code, which I suspect would be as hard a sell to netdev as expanding the secid to a lsmblob. I also thought I'd gotten netdev on the CC: for this patch, but it looks like I missed it. I did start on the UDS attribute re-do, and discovered that I was going to have to introduce new failure paths, and that it might not be possible to maintain compatibility for all cases because of the new possibilities of failure.