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Message-ID: <61d21f68-8e84-ad85-ef20-fced8c8b916d@schaufler-ca.com>
Date: Thu, 30 Mar 2023 13:55:35 -0700
From: Casey Schaufler <casey@...aufler-ca.com>
To: Paul Moore <paul@...l-moore.com>
Cc: linux-security-module@...r.kernel.org, jmorris@...ei.org,
keescook@...omium.org, john.johansen@...onical.com,
penguin-kernel@...ove.sakura.ne.jp, stephen.smalley.work@...il.com,
linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
mic@...ikod.net, selinux@...r.kernel.org,
Casey Schaufler <casey@...aufler-ca.com>
Subject: Re: [PATCH v7 10/11] SELinux: Add selfattr hooks
On 3/29/2023 6:13 PM, Paul Moore wrote:
> On Wed, Mar 15, 2023 at 6:52 PM Casey Schaufler <casey@...aufler-ca.com> wrote:
>> Add hooks for setselfattr and getselfattr. These hooks are not very
>> different from their setprocattr and getprocattr equivalents, and
>> much of the code is shared.
>>
>> Signed-off-by: Casey Schaufler <casey@...aufler-ca.com>
>> Cc: selinux@...r.kernel.org
>> Cc: Paul Moore <paul@...l-moore.com>
>> ---
>> security/selinux/hooks.c | 147 +++++++++++++++++++++++++++++++--------
>> 1 file changed, 117 insertions(+), 30 deletions(-)
>>
>> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
>> index 9403aee75981..8896edf80aa9 100644
>> --- a/security/selinux/hooks.c
>> +++ b/security/selinux/hooks.c
>> @@ -6348,8 +6348,7 @@ static void selinux_d_instantiate(struct dentry *dentry, struct inode *inode)
>> inode_doinit_with_dentry(inode, dentry);
>> }
>>
>> -static int selinux_getprocattr(struct task_struct *p,
>> - const char *name, char **value)
>> +static int do_getattr(unsigned int attr, struct task_struct *p, char **value)
> Are you ready for more naming nitpicks? ;)
I would expect nothing less. :)
> Let's call this 'selinux_lsm_getattr()', and the matching setter
> should be 'selinux_lsm_setattr()'.
As you wish. It's your LSM.
>> {
>> const struct task_security_struct *__tsec;
>> u32 sid;
>> @@ -6367,20 +6366,27 @@ static int selinux_getprocattr(struct task_struct *p,
>> goto bad;
>> }
>>
>> - if (!strcmp(name, "current"))
>> + switch (attr) {
>> + case LSM_ATTR_CURRENT:
>> sid = __tsec->sid;
>> - else if (!strcmp(name, "prev"))
>> + break;
>> + case LSM_ATTR_PREV:
>> sid = __tsec->osid;
>> - else if (!strcmp(name, "exec"))
>> + break;
>> + case LSM_ATTR_EXEC:
>> sid = __tsec->exec_sid;
>> - else if (!strcmp(name, "fscreate"))
>> + break;
>> + case LSM_ATTR_FSCREATE:
>> sid = __tsec->create_sid;
>> - else if (!strcmp(name, "keycreate"))
>> + break;
>> + case LSM_ATTR_KEYCREATE:
>> sid = __tsec->keycreate_sid;
>> - else if (!strcmp(name, "sockcreate"))
>> + break;
>> + case LSM_ATTR_SOCKCREATE:
>> sid = __tsec->sockcreate_sid;
>> - else {
>> - error = -EINVAL;
>> + break;
>> + default:
>> + error = -EOPNOTSUPP;
> The error should probably be -EINVAL.
It's possible that we may add an attribute that SELinux doesn't
support, say LSM_ATTR_CRYPTO_KEY, that another LSM does. This is
the same behavior the other LSMs exhibit in the face of a request
for attributes such as LSM_ATTR_KEYCREATE that they don't support.
>> goto bad;
>> }
>> rcu_read_unlock();
>> @@ -6398,7 +6404,7 @@ static int selinux_getprocattr(struct task_struct *p,
>> return error;
>> }
>>
>> -static int selinux_setprocattr(const char *name, void *value, size_t size)
>> +static int do_setattr(u64 attr, void *value, size_t size)
>> {
>> struct task_security_struct *tsec;
>> struct cred *new;
>> @@ -6409,28 +6415,36 @@ static int selinux_setprocattr(const char *name, void *value, size_t size)
>> /*
>> * Basic control over ability to set these attributes at all.
>> */
>> - if (!strcmp(name, "exec"))
>> + switch (attr) {
>> + case LSM_ATTR_CURRENT:
>> + error = avc_has_perm(&selinux_state,
>> + mysid, mysid, SECCLASS_PROCESS,
>> + PROCESS__SETCURRENT, NULL);
>> + break;
>> + case LSM_ATTR_EXEC:
>> error = avc_has_perm(&selinux_state,
>> mysid, mysid, SECCLASS_PROCESS,
>> PROCESS__SETEXEC, NULL);
>> - else if (!strcmp(name, "fscreate"))
>> + break;
>> + case LSM_ATTR_FSCREATE:
>> error = avc_has_perm(&selinux_state,
>> mysid, mysid, SECCLASS_PROCESS,
>> PROCESS__SETFSCREATE, NULL);
>> - else if (!strcmp(name, "keycreate"))
>> + break;
>> + case LSM_ATTR_KEYCREATE:
>> error = avc_has_perm(&selinux_state,
>> mysid, mysid, SECCLASS_PROCESS,
>> PROCESS__SETKEYCREATE, NULL);
>> - else if (!strcmp(name, "sockcreate"))
>> + break;
>> + case LSM_ATTR_SOCKCREATE:
>> error = avc_has_perm(&selinux_state,
>> mysid, mysid, SECCLASS_PROCESS,
>> PROCESS__SETSOCKCREATE, NULL);
>> - else if (!strcmp(name, "current"))
>> - error = avc_has_perm(&selinux_state,
>> - mysid, mysid, SECCLASS_PROCESS,
>> - PROCESS__SETCURRENT, NULL);
>> - else
>> - error = -EINVAL;
>> + break;
>> + default:
>> + error = -EOPNOTSUPP;
> Same as above, should be -EINVAL.
Same as above, there may be attributes SELinux doesn't support.
>> + break;
>> + }
>> if (error)
>> return error;
>>
>> @@ -6442,13 +6456,14 @@ static int selinux_setprocattr(const char *name, void *value, size_t size)
>> }
>> error = security_context_to_sid(&selinux_state, value, size,
>> &sid, GFP_KERNEL);
>> - if (error == -EINVAL && !strcmp(name, "fscreate")) {
>> + if (error == -EINVAL && attr == LSM_ATTR_FSCREATE) {
>> if (!has_cap_mac_admin(true)) {
>> struct audit_buffer *ab;
>> size_t audit_size;
>>
>> - /* We strip a nul only if it is at the end, otherwise the
>> - * context contains a nul and we should audit that */
>> + /* We strip a nul only if it is at the end,
>> + * otherwise the context contains a nul and
>> + * we should audit that */
> You *do* get gold stars for fixing line lengths in close proximity ;)
I guess I'm the Last User of the 80 character terminal.
>> if (str[size - 1] == '\0')
>> audit_size = size - 1;
>> else
>> @@ -6459,7 +6474,8 @@ static int selinux_setprocattr(const char *name, void *value, size_t size)
>> if (!ab)
>> return error;
>> audit_log_format(ab, "op=fscreate invalid_context=");
>> - audit_log_n_untrustedstring(ab, value, audit_size);
>> + audit_log_n_untrustedstring(ab, value,
>> + audit_size);
>> audit_log_end(ab);
>>
>> return error;
>> @@ -6483,11 +6499,11 @@ static int selinux_setprocattr(const char *name, void *value, size_t size)
>> checks and may_create for the file creation checks. The
>> operation will then fail if the context is not permitted. */
>> tsec = selinux_cred(new);
>> - if (!strcmp(name, "exec")) {
>> + if (attr == LSM_ATTR_EXEC) {
>> tsec->exec_sid = sid;
>> - } else if (!strcmp(name, "fscreate")) {
>> + } else if (attr == LSM_ATTR_FSCREATE) {
>> tsec->create_sid = sid;
>> - } else if (!strcmp(name, "keycreate")) {
>> + } else if (attr == LSM_ATTR_KEYCREATE) {
>> if (sid) {
>> error = avc_has_perm(&selinux_state, mysid, sid,
>> SECCLASS_KEY, KEY__CREATE, NULL);
>> @@ -6495,9 +6511,9 @@ static int selinux_setprocattr(const char *name, void *value, size_t size)
>> goto abort_change;
>> }
>> tsec->keycreate_sid = sid;
>> - } else if (!strcmp(name, "sockcreate")) {
>> + } else if (attr == LSM_ATTR_SOCKCREATE) {
>> tsec->sockcreate_sid = sid;
>> - } else if (!strcmp(name, "current")) {
>> + } else if (attr == LSM_ATTR_CURRENT) {
>> error = -EINVAL;
>> if (sid == 0)
>> goto abort_change;
>> @@ -6542,6 +6558,75 @@ static int selinux_setprocattr(const char *name, void *value, size_t size)
>> return error;
>> }
>>
>> +static int selinux_getselfattr(unsigned int __user attr,
>> + struct lsm_ctx __user *ctx, size_t *size,
>> + u32 __user flags)
>> +{
>> + char *value;
>> + size_t total_len;
>> + int len;
>> + int rc = 0;
>> +
>> + len = do_getattr(attr, current, &value);
>> + if (len < 0)
>> + return len;
>> +
>> + total_len = len + sizeof(*ctx);
>> +
>> + if (total_len > *size)
>> + rc = -E2BIG;
>> + else
>> + lsm_fill_user_ctx(ctx, value, len, LSM_ID_SELINUX, 0);
>> +
>> + *size = total_len;
>> + return rc;
>> +}
>> +
>> +static int selinux_setselfattr(unsigned int __user attr,
>> + struct lsm_ctx __user *ctx, size_t __user size,
>> + u32 __user flags)
>> +{
>> + struct lsm_ctx *lctx;
>> + void *context;
>> + int rc;
>> +
>> + context = kmalloc(size, GFP_KERNEL);
>> + if (context == NULL)
>> + return -ENOMEM;
>> +
>> + lctx = (struct lsm_ctx *)context;
>> + if (copy_from_user(context, ctx, size))
>> + rc = -EFAULT;
>> + else if (lctx->ctx_len > size)
>> + rc = -EINVAL;
>> + else
>> + rc = do_setattr(attr, lctx + 1, lctx->ctx_len);
>> +
>> + kfree(context);
>> + if (rc > 0)
>> + return 0;
>> + return rc;
>> +}
>> +
>> +static int selinux_getprocattr(struct task_struct *p,
>> + const char *name, char **value)
>> +{
>> + unsigned int attr = lsm_name_to_attr(name);
>> +
>> + if (attr)
>> + return do_getattr(attr, p, value);
>> + return -EINVAL;
>> +}
>> +
>> +static int selinux_setprocattr(const char *name, void *value, size_t size)
>> +{
>> + int attr = lsm_name_to_attr(name);
>> +
>> + if (attr)
>> + return do_setattr(attr, value, size);
>> + return -EINVAL;
>> +}
>> +
>> static int selinux_ismaclabel(const char *name)
>> {
>> return (strcmp(name, XATTR_SELINUX_SUFFIX) == 0);
>> @@ -7183,6 +7268,8 @@ static struct security_hook_list selinux_hooks[] __lsm_ro_after_init = {
>>
>> LSM_HOOK_INIT(d_instantiate, selinux_d_instantiate),
>>
>> + LSM_HOOK_INIT(getselfattr, selinux_getselfattr),
>> + LSM_HOOK_INIT(setselfattr, selinux_setselfattr),
>> LSM_HOOK_INIT(getprocattr, selinux_getprocattr),
>> LSM_HOOK_INIT(setprocattr, selinux_setprocattr),
>>
>> --
>> 2.39.2
> --
> paul-moore.com
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