| Message ID | 20220929153041.500115-11-brauner@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | acl: add vfs posix acl api | expand |
On Thu, Sep 29, 2022 at 11:31 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. SELinux 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 > these are all fairly simply hooks for SELinux. > > 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 > > /* v3 */ > Paul Moore <paul@paul-moore.com>: > - Add get, and remove acl hook > > /* v4 */ > unchanged > > security/selinux/hooks.c | 24 ++++++++++++++++++++++++ > 1 file changed, 24 insertions(+) One small nitpick below, but looks good regardless. Acked-by: Paul Moore <paul@paul-moore.com> > diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c > index 79573504783b..0e3cd67e5e92 100644 > --- a/security/selinux/hooks.c > +++ b/security/selinux/hooks.c > @@ -3239,6 +3239,27 @@ static int selinux_inode_setxattr(struct user_namespace *mnt_userns, > &ad); > } > > +static int selinux_inode_set_acl(struct user_namespace *mnt_userns, > + struct dentry *dentry, const char *acl_name, > + struct posix_acl *kacl) > +{ > + return dentry_has_perm(current_cred(), dentry, FILE__SETATTR); > +} > + > +static int selinux_inode_get_acl(struct user_namespace *mnt_userns, > + struct dentry *dentry, const char *acl_name) > +{ > + const struct cred *cred = current_cred(); > + > + return dentry_has_perm(cred, dentry, FILE__GETATTR); > +} Both the set and remove hooks use current_cred() directly in the call to dentry_has_perm(), you might as well do the same in the get hook. > +static int selinux_inode_remove_acl(struct user_namespace *mnt_userns, > + struct dentry *dentry, const char *acl_name) > +{ > + return dentry_has_perm(current_cred(), dentry, FILE__SETATTR); > +} -- paul-moore.com
On Thu, Sep 29, 2022 at 03:15:17PM -0400, Paul Moore wrote: > On Thu, Sep 29, 2022 at 11:31 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. SELinux 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 > > these are all fairly simply hooks for SELinux. > > > > 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 > > > > /* v3 */ > > Paul Moore <paul@paul-moore.com>: > > - Add get, and remove acl hook > > > > /* v4 */ > > unchanged > > > > security/selinux/hooks.c | 24 ++++++++++++++++++++++++ > > 1 file changed, 24 insertions(+) > > One small nitpick below, but looks good regardless. > > Acked-by: Paul Moore <paul@paul-moore.com> > > > diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c > > index 79573504783b..0e3cd67e5e92 100644 > > --- a/security/selinux/hooks.c > > +++ b/security/selinux/hooks.c > > @@ -3239,6 +3239,27 @@ static int selinux_inode_setxattr(struct user_namespace *mnt_userns, > > &ad); > > } > > > > +static int selinux_inode_set_acl(struct user_namespace *mnt_userns, > > + struct dentry *dentry, const char *acl_name, > > + struct posix_acl *kacl) > > +{ > > + return dentry_has_perm(current_cred(), dentry, FILE__SETATTR); > > +} > > + > > +static int selinux_inode_get_acl(struct user_namespace *mnt_userns, > > + struct dentry *dentry, const char *acl_name) > > +{ > > + const struct cred *cred = current_cred(); > > + > > + return dentry_has_perm(cred, dentry, FILE__GETATTR); > > +} > > Both the set and remove hooks use current_cred() directly in the call > to dentry_has_perm(), you might as well do the same in the get hook. Done.
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c index 79573504783b..0e3cd67e5e92 100644 --- a/security/selinux/hooks.c +++ b/security/selinux/hooks.c @@ -3239,6 +3239,27 @@ static int selinux_inode_setxattr(struct user_namespace *mnt_userns, &ad); } +static int selinux_inode_set_acl(struct user_namespace *mnt_userns, + struct dentry *dentry, const char *acl_name, + struct posix_acl *kacl) +{ + return dentry_has_perm(current_cred(), dentry, FILE__SETATTR); +} + +static int selinux_inode_get_acl(struct user_namespace *mnt_userns, + struct dentry *dentry, const char *acl_name) +{ + const struct cred *cred = current_cred(); + + return dentry_has_perm(cred, dentry, FILE__GETATTR); +} + +static int selinux_inode_remove_acl(struct user_namespace *mnt_userns, + struct dentry *dentry, const char *acl_name) +{ + return dentry_has_perm(current_cred(), dentry, FILE__SETATTR); +} + static void selinux_inode_post_setxattr(struct dentry *dentry, const char *name, const void *value, size_t size, int flags) @@ -7063,6 +7084,9 @@ static struct security_hook_list selinux_hooks[] __lsm_ro_after_init = { LSM_HOOK_INIT(inode_getxattr, selinux_inode_getxattr), LSM_HOOK_INIT(inode_listxattr, selinux_inode_listxattr), LSM_HOOK_INIT(inode_removexattr, selinux_inode_removexattr), + LSM_HOOK_INIT(inode_set_acl, selinux_inode_set_acl), + LSM_HOOK_INIT(inode_get_acl, selinux_inode_get_acl), + LSM_HOOK_INIT(inode_remove_acl, selinux_inode_remove_acl), LSM_HOOK_INIT(inode_getsecurity, selinux_inode_getsecurity), LSM_HOOK_INIT(inode_setsecurity, selinux_inode_setsecurity), LSM_HOOK_INIT(inode_listsecurity, selinux_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. SELinux 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 these are all fairly simply hooks for SELinux. 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 /* v3 */ Paul Moore <paul@paul-moore.com>: - Add get, and remove acl hook /* v4 */ unchanged security/selinux/hooks.c | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+)