| Message ID | 20220926140827.142806-13-brauner@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | acl: add vfs posix acl api | expand |
On Mon, Sep 26, 2022 at 11:24 AM Christian Brauner <brauner@kernel.org> wrote: > > The current way of setting and getting posix acls through the generic > xattr interface is error prone and type unsafe. The vfs needs to > interpret and fixup posix acls before storing or reporting it to > userspace. Various hacks exist to make this work. The code is hard to > understand and difficult to maintain in it's current form. Instead of > making this work by hacking posix acls through xattr handlers we are > building a dedicated posix acl api around the get and set inode > operations. This removes a lot of hackiness and makes the codepaths > easier to maintain. A lot of background can be found in [1]. > > So far posix acls were passed as a void blob to the security and > integrity modules. Some of them like evm then proceed to interpret the > void pointer and convert it into the kernel internal struct posix acl > representation to perform their integrity checking magic. This is > obviously pretty problematic as that requires knowledge that only the > vfs is guaranteed to have and has lead to various bugs. Add a proper > security hook for setting posix acls and pass down the posix acls in > their appropriate vfs format instead of hacking it through a void > pointer stored in the uapi format. > > I spent considerate time in the security module infrastructure and > audited all codepaths. Smack has no restrictions based on the posix > acl values passed through it. The capability hook doesn't need to be > called either because it only has restrictions on security.* xattrs. So > this all becomes a very simple hook for smack. > > Link: https://lore.kernel.org/all/20220801145520.1532837-1-brauner@kernel.org [1] > Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org> > --- > > Notes: > /* v2 */ > unchanged > > security/smack/smack_lsm.c | 24 ++++++++++++++++++++++++ > 1 file changed, 24 insertions(+) Reviewed-by: Paul Moore <paul@paul-moore.com> -- paul-moore.com
On 9/26/2022 7:08 AM, Christian Brauner wrote: > The current way of setting and getting posix acls through the generic > xattr interface is error prone and type unsafe. The vfs needs to > interpret and fixup posix acls before storing or reporting it to > userspace. Various hacks exist to make this work. The code is hard to > understand and difficult to maintain in it's current form. Instead of > making this work by hacking posix acls through xattr handlers we are > building a dedicated posix acl api around the get and set inode > operations. This removes a lot of hackiness and makes the codepaths > easier to maintain. A lot of background can be found in [1]. > > So far posix acls were passed as a void blob to the security and > integrity modules. Some of them like evm then proceed to interpret the > void pointer and convert it into the kernel internal struct posix acl > representation to perform their integrity checking magic. This is > obviously pretty problematic as that requires knowledge that only the > vfs is guaranteed to have and has lead to various bugs. Add a proper > security hook for setting posix acls and pass down the posix acls in > their appropriate vfs format instead of hacking it through a void > pointer stored in the uapi format. > > I spent considerate time in the security module infrastructure and > audited all codepaths. Smack has no restrictions based on the posix > acl values passed through it. The capability hook doesn't need to be > called either because it only has restrictions on security.* xattrs. So > this all becomes a very simple hook for smack. > > Link: https://lore.kernel.org/all/20220801145520.1532837-1-brauner@kernel.org [1] > Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org> The Smack hook looks fine. Acked-by: Casey Schaufler <casey@schaufler-ca.com> > --- > > Notes: > /* v2 */ > unchanged > > security/smack/smack_lsm.c | 24 ++++++++++++++++++++++++ > 1 file changed, 24 insertions(+) > > diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c > index 001831458fa2..ec6d55632b4f 100644 > --- a/security/smack/smack_lsm.c > +++ b/security/smack/smack_lsm.c > @@ -1393,6 +1393,29 @@ static int smack_inode_removexattr(struct user_namespace *mnt_userns, > return 0; > } > > +/** > + * smack_inode_set_acl - Smack check for setting posix acls > + * @mnt_userns: the userns attached to the mnt this request came from > + * @dentry: the object > + * @acl_name: name of the posix acl > + * @kacl: the posix acls > + * > + * Returns 0 if access is permitted, an error code otherwise > + */ > +static int smack_inode_set_acl(struct user_namespace *mnt_userns, > + struct dentry *dentry, const char *acl_name, > + struct posix_acl *kacl) > +{ > + struct smk_audit_info ad; > + int rc; > + > + smk_ad_init(&ad, __func__, LSM_AUDIT_DATA_DENTRY); > + smk_ad_setfield_u_fs_path_dentry(&ad, dentry); > + rc = smk_curacc(smk_of_inode(d_backing_inode(dentry)), MAY_WRITE, &ad); > + rc = smk_bu_inode(d_backing_inode(dentry), MAY_WRITE, rc); > + return rc; > +} > + > /** > * smack_inode_getsecurity - get smack xattrs > * @mnt_userns: active user namespace > @@ -4772,6 +4795,7 @@ static struct security_hook_list smack_hooks[] __lsm_ro_after_init = { > LSM_HOOK_INIT(inode_post_setxattr, smack_inode_post_setxattr), > LSM_HOOK_INIT(inode_getxattr, smack_inode_getxattr), > LSM_HOOK_INIT(inode_removexattr, smack_inode_removexattr), > + LSM_HOOK_INIT(inode_set_acl, smack_inode_set_acl), > LSM_HOOK_INIT(inode_getsecurity, smack_inode_getsecurity), > LSM_HOOK_INIT(inode_setsecurity, smack_inode_setsecurity), > LSM_HOOK_INIT(inode_listsecurity, smack_inode_listsecurity),
diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c index 001831458fa2..ec6d55632b4f 100644 --- a/security/smack/smack_lsm.c +++ b/security/smack/smack_lsm.c @@ -1393,6 +1393,29 @@ static int smack_inode_removexattr(struct user_namespace *mnt_userns, return 0; } +/** + * smack_inode_set_acl - Smack check for setting posix acls + * @mnt_userns: the userns attached to the mnt this request came from + * @dentry: the object + * @acl_name: name of the posix acl + * @kacl: the posix acls + * + * Returns 0 if access is permitted, an error code otherwise + */ +static int smack_inode_set_acl(struct user_namespace *mnt_userns, + struct dentry *dentry, const char *acl_name, + struct posix_acl *kacl) +{ + struct smk_audit_info ad; + int rc; + + smk_ad_init(&ad, __func__, LSM_AUDIT_DATA_DENTRY); + smk_ad_setfield_u_fs_path_dentry(&ad, dentry); + rc = smk_curacc(smk_of_inode(d_backing_inode(dentry)), MAY_WRITE, &ad); + rc = smk_bu_inode(d_backing_inode(dentry), MAY_WRITE, rc); + return rc; +} + /** * smack_inode_getsecurity - get smack xattrs * @mnt_userns: active user namespace @@ -4772,6 +4795,7 @@ static struct security_hook_list smack_hooks[] __lsm_ro_after_init = { LSM_HOOK_INIT(inode_post_setxattr, smack_inode_post_setxattr), LSM_HOOK_INIT(inode_getxattr, smack_inode_getxattr), LSM_HOOK_INIT(inode_removexattr, smack_inode_removexattr), + LSM_HOOK_INIT(inode_set_acl, smack_inode_set_acl), LSM_HOOK_INIT(inode_getsecurity, smack_inode_getsecurity), LSM_HOOK_INIT(inode_setsecurity, smack_inode_setsecurity), LSM_HOOK_INIT(inode_listsecurity, smack_inode_listsecurity),
The current way of setting and getting posix acls through the generic xattr interface is error prone and type unsafe. The vfs needs to interpret and fixup posix acls before storing or reporting it to userspace. Various hacks exist to make this work. The code is hard to understand and difficult to maintain in it's current form. Instead of making this work by hacking posix acls through xattr handlers we are building a dedicated posix acl api around the get and set inode operations. This removes a lot of hackiness and makes the codepaths easier to maintain. A lot of background can be found in [1]. So far posix acls were passed as a void blob to the security and integrity modules. Some of them like evm then proceed to interpret the void pointer and convert it into the kernel internal struct posix acl representation to perform their integrity checking magic. This is obviously pretty problematic as that requires knowledge that only the vfs is guaranteed to have and has lead to various bugs. Add a proper security hook for setting posix acls and pass down the posix acls in their appropriate vfs format instead of hacking it through a void pointer stored in the uapi format. I spent considerate time in the security module infrastructure and audited all codepaths. Smack has no restrictions based on the posix acl values passed through it. The capability hook doesn't need to be called either because it only has restrictions on security.* xattrs. So this all becomes a very simple hook for smack. Link: https://lore.kernel.org/all/20220801145520.1532837-1-brauner@kernel.org [1] Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org> --- Notes: /* v2 */ unchanged security/smack/smack_lsm.c | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+)