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Message-ID: <fd1981c0-3f64-adb5-dece-a25494119992@schaufler-ca.com>
Date: Wed, 6 Sep 2023 16:48:04 -0700
From: Casey Schaufler <casey@...aufler-ca.com>
To: Paul Moore <paul@...l-moore.com>,
linux-security-module@...r.kernel.org
Cc: jmorris@...ei.org, serge@...lyn.com, 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,
Casey Schaufler <casey@...aufler-ca.com>
Subject: Re: [PATCH v14 4/11] LSM: syscalls for current process attributes
On 9/6/2023 4:22 PM, Paul Moore wrote:
> On Aug 28, 2023 Casey Schaufler <casey@...aufler-ca.com> wrote:
>> Create a system call lsm_get_self_attr() to provide the security
>> module maintained attributes of the current process.
>> Create a system call lsm_set_self_attr() to set a security
>> module maintained attribute of the current process.
>> Historically these attributes have been exposed to user space via
>> entries in procfs under /proc/self/attr.
>>
>> The attribute value is provided in a lsm_ctx structure. The structure
>> identifies the size of the attribute, and the attribute value. The format
>> of the attribute value is defined by the security module. A flags field
>> is included for LSM specific information. It is currently unused and must
>> be 0. The total size of the data, including the lsm_ctx structure and any
>> padding, is maintained as well.
>>
>> struct lsm_ctx {
>> __u64 id;
>> __u64 flags;
>> __u64 len;
>> __u64 ctx_len;
>> __u8 ctx[];
>> };
>>
>> Two new LSM hooks are used to interface with the LSMs.
>> security_getselfattr() collects the lsm_ctx values from the
>> LSMs that support the hook, accounting for space requirements.
>> security_setselfattr() identifies which LSM the attribute is
>> intended for and passes it along.
>>
>> Signed-off-by: Casey Schaufler <casey@...aufler-ca.com>
>> Reviewed-by: Kees Cook <keescook@...omium.org>
>> Reviewed-by: Serge Hallyn <serge@...lyn.com>
>> Reviewed-by: John Johansen <john.johansen@...onical.com>
>> ---
>> Documentation/userspace-api/lsm.rst | 70 +++++++++++++
>> include/linux/lsm_hook_defs.h | 4 +
>> include/linux/lsm_hooks.h | 1 +
>> include/linux/security.h | 19 ++++
>> include/linux/syscalls.h | 5 +
>> include/uapi/linux/lsm.h | 36 +++++++
>> kernel/sys_ni.c | 2 +
>> security/Makefile | 1 +
>> security/lsm_syscalls.c | 57 +++++++++++
>> security/security.c | 146 ++++++++++++++++++++++++++++
>> 10 files changed, 341 insertions(+)
>> create mode 100644 Documentation/userspace-api/lsm.rst
>> create mode 100644 security/lsm_syscalls.c
> ..
>
>> diff --git a/security/security.c b/security/security.c
>> index 82253294069c..aa4ade1f71b9 100644
>> --- a/security/security.c
>> +++ b/security/security.c
>> @@ -3798,6 +3798,152 @@ void security_d_instantiate(struct dentry *dentry, struct inode *inode)
>> }
>> EXPORT_SYMBOL(security_d_instantiate);
>>
>> +/**
>> + * security_getselfattr - Read an LSM attribute of the current process.
>> + * @attr: which attribute to return
>> + * @uctx: the user-space destination for the information, or NULL
>> + * @size: pointer to the size of space available to receive the data
>> + * @flags: special handling options. LSM_FLAG_SINGLE indicates that only
>> + * attributes associated with the LSM identified in the passed @ctx be
>> + * reported.
>> + *
>> + * A NULL value for @uctx can be used to get both the number of attributes
>> + * and the size of the data.
>> + *
>> + * Returns the number of attributes found on success, negative value
>> + * on error. @size is reset to the total size of the data.
>> + * If @size is insufficient to contain the data -E2BIG is returned.
>> + */
>> +int security_getselfattr(unsigned int attr, struct lsm_ctx __user *uctx,
>> + size_t __user *size, u32 flags)
>> +{
>> + struct security_hook_list *hp;
>> + struct lsm_ctx lctx = { .id = LSM_ID_UNDEF, };
>> + u8 __user *base = (u8 __user *)uctx;
>> + size_t total = 0;
>> + size_t entrysize;
>> + size_t left;
>> + bool toobig = false;
>> + bool single = false;
>> + int count = 0;
>> + int rc;
>> +
>> + if (attr == LSM_ATTR_UNDEF)
>> + return -EINVAL;
>> + if (size == NULL)
>> + return -EINVAL;
>> + if (get_user(left, size))
>> + return -EFAULT;
>> +
>> + if (flags) {
>> + /*
>> + * Only flag supported is LSM_FLAG_SINGLE
>> + */
>> + if (flags & LSM_FLAG_SINGLE)
>> + return -EINVAL;
> Should this be something like the following?
>
> if (flags & ~LSM_FLAG_SINGLE)
> return -EINVAL;
Yes. I have a fix ready. There are a couple other touch-ups, too.
>
>> + if (uctx &&
>> + copy_struct_from_user(&lctx, sizeof(lctx), uctx, left))
>> + return -EFAULT;
>> + /*
>> + * If the LSM ID isn't specified it is an error.
>> + */
>> + if (lctx.id == LSM_ID_UNDEF)
>> + return -EINVAL;
>> + single = true;
>> + }
>> +
>> + /*
>> + * In the usual case gather all the data from the LSMs.
>> + * In the single case only get the data from the LSM specified.
>> + */
>> + hlist_for_each_entry(hp, &security_hook_heads.getselfattr, list) {
>> + if (single) {
>> + if (count > 0)
>> + break;
>> + if (lctx.id != hp->lsmid->id)
>> + continue;
>> + }
>> + entrysize = left;
>> + if (base)
>> + uctx = (struct lsm_ctx __user *)(base + total);
>> + rc = hp->hook.getselfattr(attr, uctx, &entrysize, flags);
>> + if (rc == -EOPNOTSUPP) {
>> + rc = 0;
>> + continue;
>> + }
>> + if (rc == -E2BIG) {
>> + toobig = true;
>> + left = 0;
>> + total += entrysize;
>> + continue;
>> + }
>> + if (rc < 0)
>> + return rc;
>> +
>> + left -= entrysize;
>> + total += entrysize;
>> + count += rc;
>> + }
>> + if (put_user(total, size))
>> + return -EFAULT;
>> + if (toobig)
>> + return -E2BIG;
>> + if (count == 0)
>> + return LSM_RET_DEFAULT(getselfattr);
>> + return count;
>> +}
>
> --
> paul-moore.com
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