| Message ID | 20220926140827.142806-19-brauner@kernel.org (mailing list archive) |
|---|---|
| State | Superseded |
| Delegated to: | Paul Moore |
| 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 posix acl api provides a dedicated security and integrity hook for > setting posix acls. This means that > > evm_protect_xattr() > -> evm_xattr_change() > -> evm_xattr_acl_change() > > is now only hit during vfs_remove_acl() at which point we are guaranteed > that xattr_value and xattr_value_len are NULL and 0. In this case evm > always used to return 1. Simplify this function to do just that. > > Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org> > --- > > Notes: > /* v2 */ > unchanged > > security/integrity/evm/evm_main.c | 62 +++++++------------------------ > 1 file changed, 14 insertions(+), 48 deletions(-) > > diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c > index 15aa5995fff4..1fbe1b8d0364 100644 > --- a/security/integrity/evm/evm_main.c > +++ b/security/integrity/evm/evm_main.c > @@ -436,62 +436,29 @@ static enum integrity_status evm_verify_current_integrity(struct dentry *dentry) > > /* > * evm_xattr_acl_change - check if passed ACL changes the inode mode > - * @mnt_userns: user namespace of the idmapped mount > - * @dentry: pointer to the affected dentry > * @xattr_name: requested xattr > * @xattr_value: requested xattr value > * @xattr_value_len: requested xattr value length > * > - * Check if passed ACL changes the inode mode, which is protected by EVM. > + * This is only hit during xattr removal at which point we always return 1. > + * Splat a warning in case someone managed to pass data to this function. That > + * should never happen. > * > * Returns 1 if passed ACL causes inode mode change, 0 otherwise. > */ > -static int evm_xattr_acl_change(struct user_namespace *mnt_userns, > - struct dentry *dentry, const char *xattr_name, > - const void *xattr_value, size_t xattr_value_len) > +static int evm_xattr_acl_change(const void *xattr_value, size_t xattr_value_len) > { > -#ifdef CONFIG_FS_POSIX_ACL > - umode_t mode; > - struct posix_acl *acl = NULL, *acl_res; > - struct inode *inode = d_backing_inode(dentry); > - int rc; > - > - /* > - * An earlier comment here mentioned that the idmappings for > - * ACL_{GROUP,USER} don't matter since EVM is only interested in the > - * mode stored as part of POSIX ACLs. Nonetheless, if it must translate > - * from the uapi POSIX ACL representation to the VFS internal POSIX ACL > - * representation it should do so correctly. There's no guarantee that > - * we won't change POSIX ACLs in a way that ACL_{GROUP,USER} matters > - * for the mode at some point and it's difficult to keep track of all > - * the LSM and integrity modules and what they do to POSIX ACLs. > - * > - * Frankly, EVM shouldn't try to interpret the uapi struct for POSIX > - * ACLs it received. It requires knowledge that only the VFS is > - * guaranteed to have. > - */ > - acl = vfs_set_acl_prepare(mnt_userns, i_user_ns(inode), > - xattr_value, xattr_value_len); > - if (IS_ERR_OR_NULL(acl)) > - return 1; > - > - acl_res = acl; > - /* > - * Passing mnt_userns is necessary to correctly determine the GID in > - * an idmapped mount, as the GID is used to clear the setgid bit in > - * the inode mode. > - */ > - rc = posix_acl_update_mode(mnt_userns, inode, &mode, &acl_res); > - > - posix_acl_release(acl); > - > - if (rc) > - return 1; > + int rc = 0; > > - if (inode->i_mode != mode) > - return 1; > +#ifdef CONFIG_FS_POSIX_ACL > + WARN_ONCE(xattr_value != NULL, > + "Passing xattr value for POSIX ACLs not supported\n"); > + WARN_ONCE(xattr_value_len != 0, > + "Passing non-zero length for POSIX ACLs not supported\n"); > + rc = 1; > #endif > - return 0; > + > + return rc; > } This is another case where I'll leave the final say up to Mimi, but why not just get rid of evm_xattr_acl_change() entirely? Unless I'm missing something, it's only reason for existing now is to check that it is passed the proper (empty) parameters which seems pointless ... no? -- paul-moore.com
On Tue, Sep 27, 2022 at 06:56:44PM -0400, Paul Moore wrote: > On Mon, Sep 26, 2022 at 11:24 AM Christian Brauner <brauner@kernel.org> wrote: > > > > The posix acl api provides a dedicated security and integrity hook for > > setting posix acls. This means that > > > > evm_protect_xattr() > > -> evm_xattr_change() > > -> evm_xattr_acl_change() > > > > is now only hit during vfs_remove_acl() at which point we are guaranteed > > that xattr_value and xattr_value_len are NULL and 0. In this case evm > > always used to return 1. Simplify this function to do just that. > > > > Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org> > > --- > > > > Notes: > > /* v2 */ > > unchanged > > > > security/integrity/evm/evm_main.c | 62 +++++++------------------------ > > 1 file changed, 14 insertions(+), 48 deletions(-) > > > > diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c > > index 15aa5995fff4..1fbe1b8d0364 100644 > > --- a/security/integrity/evm/evm_main.c > > +++ b/security/integrity/evm/evm_main.c > > @@ -436,62 +436,29 @@ static enum integrity_status evm_verify_current_integrity(struct dentry *dentry) > > > > /* > > * evm_xattr_acl_change - check if passed ACL changes the inode mode > > - * @mnt_userns: user namespace of the idmapped mount > > - * @dentry: pointer to the affected dentry > > * @xattr_name: requested xattr > > * @xattr_value: requested xattr value > > * @xattr_value_len: requested xattr value length > > * > > - * Check if passed ACL changes the inode mode, which is protected by EVM. > > + * This is only hit during xattr removal at which point we always return 1. > > + * Splat a warning in case someone managed to pass data to this function. That > > + * should never happen. > > * > > * Returns 1 if passed ACL causes inode mode change, 0 otherwise. > > */ > > -static int evm_xattr_acl_change(struct user_namespace *mnt_userns, > > - struct dentry *dentry, const char *xattr_name, > > - const void *xattr_value, size_t xattr_value_len) > > +static int evm_xattr_acl_change(const void *xattr_value, size_t xattr_value_len) > > { > > -#ifdef CONFIG_FS_POSIX_ACL > > - umode_t mode; > > - struct posix_acl *acl = NULL, *acl_res; > > - struct inode *inode = d_backing_inode(dentry); > > - int rc; > > - > > - /* > > - * An earlier comment here mentioned that the idmappings for > > - * ACL_{GROUP,USER} don't matter since EVM is only interested in the > > - * mode stored as part of POSIX ACLs. Nonetheless, if it must translate > > - * from the uapi POSIX ACL representation to the VFS internal POSIX ACL > > - * representation it should do so correctly. There's no guarantee that > > - * we won't change POSIX ACLs in a way that ACL_{GROUP,USER} matters > > - * for the mode at some point and it's difficult to keep track of all > > - * the LSM and integrity modules and what they do to POSIX ACLs. > > - * > > - * Frankly, EVM shouldn't try to interpret the uapi struct for POSIX > > - * ACLs it received. It requires knowledge that only the VFS is > > - * guaranteed to have. > > - */ > > - acl = vfs_set_acl_prepare(mnt_userns, i_user_ns(inode), > > - xattr_value, xattr_value_len); > > - if (IS_ERR_OR_NULL(acl)) > > - return 1; > > - > > - acl_res = acl; > > - /* > > - * Passing mnt_userns is necessary to correctly determine the GID in > > - * an idmapped mount, as the GID is used to clear the setgid bit in > > - * the inode mode. > > - */ > > - rc = posix_acl_update_mode(mnt_userns, inode, &mode, &acl_res); > > - > > - posix_acl_release(acl); > > - > > - if (rc) > > - return 1; > > + int rc = 0; > > > > - if (inode->i_mode != mode) > > - return 1; > > +#ifdef CONFIG_FS_POSIX_ACL > > + WARN_ONCE(xattr_value != NULL, > > + "Passing xattr value for POSIX ACLs not supported\n"); > > + WARN_ONCE(xattr_value_len != 0, > > + "Passing non-zero length for POSIX ACLs not supported\n"); > > + rc = 1; > > #endif > > - return 0; > > + > > + return rc; > > } > > This is another case where I'll leave the final say up to Mimi, but > why not just get rid of evm_xattr_acl_change() entirely? Unless I'm > missing something, it's only reason for existing now is to check that > it is passed the proper (empty) parameters which seems pointless ... > no? Yeah, I think we can remove it. evm_inode_remove_acl() is just evm_inode_set_acl(NULL, 0) so if we add evm_inode_remove_acl() as a wrapper around it instead of simply abusing the existing evm_inode_removexattr() we can delete all that code indeed as it won't be reachable from generic xattr code anymore.
diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c index 15aa5995fff4..1fbe1b8d0364 100644 --- a/security/integrity/evm/evm_main.c +++ b/security/integrity/evm/evm_main.c @@ -436,62 +436,29 @@ static enum integrity_status evm_verify_current_integrity(struct dentry *dentry) /* * evm_xattr_acl_change - check if passed ACL changes the inode mode - * @mnt_userns: user namespace of the idmapped mount - * @dentry: pointer to the affected dentry * @xattr_name: requested xattr * @xattr_value: requested xattr value * @xattr_value_len: requested xattr value length * - * Check if passed ACL changes the inode mode, which is protected by EVM. + * This is only hit during xattr removal at which point we always return 1. + * Splat a warning in case someone managed to pass data to this function. That + * should never happen. * * Returns 1 if passed ACL causes inode mode change, 0 otherwise. */ -static int evm_xattr_acl_change(struct user_namespace *mnt_userns, - struct dentry *dentry, const char *xattr_name, - const void *xattr_value, size_t xattr_value_len) +static int evm_xattr_acl_change(const void *xattr_value, size_t xattr_value_len) { -#ifdef CONFIG_FS_POSIX_ACL - umode_t mode; - struct posix_acl *acl = NULL, *acl_res; - struct inode *inode = d_backing_inode(dentry); - int rc; - - /* - * An earlier comment here mentioned that the idmappings for - * ACL_{GROUP,USER} don't matter since EVM is only interested in the - * mode stored as part of POSIX ACLs. Nonetheless, if it must translate - * from the uapi POSIX ACL representation to the VFS internal POSIX ACL - * representation it should do so correctly. There's no guarantee that - * we won't change POSIX ACLs in a way that ACL_{GROUP,USER} matters - * for the mode at some point and it's difficult to keep track of all - * the LSM and integrity modules and what they do to POSIX ACLs. - * - * Frankly, EVM shouldn't try to interpret the uapi struct for POSIX - * ACLs it received. It requires knowledge that only the VFS is - * guaranteed to have. - */ - acl = vfs_set_acl_prepare(mnt_userns, i_user_ns(inode), - xattr_value, xattr_value_len); - if (IS_ERR_OR_NULL(acl)) - return 1; - - acl_res = acl; - /* - * Passing mnt_userns is necessary to correctly determine the GID in - * an idmapped mount, as the GID is used to clear the setgid bit in - * the inode mode. - */ - rc = posix_acl_update_mode(mnt_userns, inode, &mode, &acl_res); - - posix_acl_release(acl); - - if (rc) - return 1; + int rc = 0; - if (inode->i_mode != mode) - return 1; +#ifdef CONFIG_FS_POSIX_ACL + WARN_ONCE(xattr_value != NULL, + "Passing xattr value for POSIX ACLs not supported\n"); + WARN_ONCE(xattr_value_len != 0, + "Passing non-zero length for POSIX ACLs not supported\n"); + rc = 1; #endif - return 0; + + return rc; } /* @@ -514,8 +481,7 @@ static int evm_xattr_change(struct user_namespace *mnt_userns, int rc = 0; if (posix_xattr_acl(xattr_name)) - return evm_xattr_acl_change(mnt_userns, dentry, xattr_name, - xattr_value, xattr_value_len); + return evm_xattr_acl_change(xattr_value, xattr_value_len); rc = vfs_getxattr_alloc(&init_user_ns, dentry, xattr_name, &xattr_data, 0, GFP_NOFS);
The posix acl api provides a dedicated security and integrity hook for setting posix acls. This means that evm_protect_xattr() -> evm_xattr_change() -> evm_xattr_acl_change() is now only hit during vfs_remove_acl() at which point we are guaranteed that xattr_value and xattr_value_len are NULL and 0. In this case evm always used to return 1. Simplify this function to do just that. Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org> --- Notes: /* v2 */ unchanged security/integrity/evm/evm_main.c | 62 +++++++------------------------ 1 file changed, 14 insertions(+), 48 deletions(-)