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    SubjectRe: [PATCH v6 04/11] LSM: syscalls for current process attributes
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    On 3/7/2023 3:56 AM, Mickaël Salaün wrote:
    > Let's say an LSM need to pass a file descriptor instead of a text
    > value. Would that be possible or would it need to use another interface?

    You could use this interface. LSM_ATTR_MAGICFD would have a
    ctx_len = sizeof(fd) and the value in ctx. The underlying
    plumbing is another matter entirely. It's likely you'd need
    to provide more information in the ctx than the fd, but I
    couldn't say what it would be, and I won't speculate.

    I would not advocate such a use, as I am not now nor have
    ever been a fan of passed file descriptors.

    >
    >
    > On 22/02/2023 21:08, Casey Schaufler 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
    >> identifys 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.

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