On Sat, Jun 3, 2023 at 3:16 PM Roberto Sassu <roberto.sassu@xxxxxxxxxxxxxxx> wrote: > From: Roberto Sassu <roberto.sassu@xxxxxxxxxx> > > Currently, the LSM infrastructure supports only one LSM providing an xattr > and EVM calculating the HMAC on that xattr, plus other inode metadata. > > Allow all LSMs to provide one or multiple xattrs, by extending the security > blob reservation mechanism. Introduce the new lbs_xattr_count field of the > lsm_blob_sizes structure, so that each LSM can specify how many xattrs it > needs, and the LSM infrastructure knows how many xattr slots it should > allocate. > > Modify the inode_init_security hook definition, by passing the full > xattr array allocated in security_inode_init_security(), and the current > number of xattr slots in that array filled by LSMs. The first parameter > would allow EVM to access and calculate the HMAC on xattrs supplied by > other LSMs, the second to not leave gaps in the xattr array, when an LSM > requested but did not provide xattrs (e.g. if it is not initialized). > > Introduce lsm_get_xattr_slot(), which LSMs can call as many times as the > number specified in the lbs_xattr_count field of the lsm_blob_sizes > structure. During each call, lsm_get_xattr_slot() increments the number of > filled xattrs, so that at the next invocation it returns the next xattr > slot to fill. > > Cleanup security_inode_init_security(). Unify the !initxattrs and > initxattrs case by simply not allocating the new_xattrs array in the > former. Update the documentation to reflect the changes, and fix the > description of the xattr name, as it is not allocated anymore. > > Adapt both SELinux and Smack to use the new definition of the > inode_init_security hook, and to call lsm_get_xattr_slot() to obtain and > fill the reserved slots in the xattr array. > > Move the xattr->name assignment after the xattr->value one, so that it is > done only in case of successful memory allocation. > > Finally, change the default return value of the inode_init_security hook > from zero to -EOPNOTSUPP, so that BPF LSM correctly follows the hook > conventions. > > Reported-by: Nicolas Bouchinet <nicolas.bouchinet@xxxxxxxxxxx> (EVM crash) > Link: https://lore.kernel.org/linux-integrity/Y1FTSIo+1x+4X0LS@archlinux/ > Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx> > --- > include/linux/lsm_hook_defs.h | 6 +-- > include/linux/lsm_hooks.h | 20 ++++++++++ > security/security.c | 71 +++++++++++++++++++++++------------ > security/selinux/hooks.c | 17 +++++---- > security/smack/smack_lsm.c | 25 ++++++------ > 5 files changed, 92 insertions(+), 47 deletions(-) ... > diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h > index ab2b2fafa4a..069ac73a84b 100644 > --- a/include/linux/lsm_hooks.h > +++ b/include/linux/lsm_hooks.h > @@ -63,8 +64,27 @@ struct lsm_blob_sizes { > int lbs_ipc; > int lbs_msg_msg; > int lbs_task; > + int lbs_xattr_count; /* number of xattr slots in new_xattrs array */ > }; > > +/** > + * lsm_get_xattr_slot - Return the next available slot and increment the index > + * @xattrs: array storing LSM-provided xattrs > + * @xattr_count: number of already stored xattrs (updated) > + * > + * Retrieve the first available slot in the @xattrs array to fill with an xattr, > + * and increment @xattr_count. > + * > + * Return: The slot to fill in @xattrs if non-NULL, NULL otherwise. > + */ > +static inline struct xattr *lsm_get_xattr_slot(struct xattr *xattrs, > + int *xattr_count) > +{ > + if (unlikely(!xattrs)) > + return NULL; > + return xattrs + (*xattr_count)++; I would have tried to avoid the pointer math by writing the above like the line below: return &xattrs[(*xattr_count)++] ... but I wouldn't worry about that, what you have is fine; I only mention this in case you need to respin this patchset for some other reason. -- paul-moore.com
