3:44 p.m.
On 7/30/2020 3:03 AM, John Johansen wrote:
On 7/24/20 1:32 PM, Casey Schaufler wrote:
> Add an entry /proc/.../attr/context which displays the full
> process security "context" in compound format:
> lsm1\0value\0lsm2\0value\0...
> This entry is not writable.
>
> A security module may decide that its policy does not allow
> this information to be displayed. In this case none of the
> information will be displayed.
>
> Reviewed-by: Kees Cook <keescook(a)chromium.org>
> Signed-off-by: Casey Schaufler <casey(a)schaufler-ca.com>
> Cc: linux-api(a)vger.kernel.org
> ---
> Documentation/security/lsm.rst | 28 +++++++++++
> fs/proc/base.c | 1 +
> include/linux/lsm_hooks.h | 6 +++
> security/apparmor/include/procattr.h | 2 +-
> security/apparmor/lsm.c | 8 +++-
> security/apparmor/procattr.c | 22 +++++----
> security/security.c | 70 ++++++++++++++++++++++++++++
> security/selinux/hooks.c | 2 +-
> security/smack/smack_lsm.c | 2 +-
> 9 files changed, 126 insertions(+), 15 deletions(-)
<snip>
>
> /**
> diff --git a/security/security.c b/security/security.c
> index d35e578fa45b..bce6be720401 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -754,6 +754,48 @@ static void __init lsm_early_task(struct task_struct *task)
> panic("%s: Early task alloc failed.\n", __func__);
> }
>
> +/**
> + * append_ctx - append a lsm/context pair to a compound context
> + * @ctx: the existing compound context
> + * @ctxlen: size of the old context, including terminating nul byte
> + * @lsm: new lsm name, nul terminated
> + * @new: new context, possibly nul terminated
> + * @newlen: maximum size of @new
> + *
> + * replace @ctx with a new compound context, appending @newlsm and @new
> + * to @ctx. On exit the new data replaces the old, which is freed.
> + * @ctxlen is set to the new size, which includes a trailing nul byte.
> + *
> + * Returns 0 on success, -ENOMEM if no memory is available.
> + */
> +static int append_ctx(char **ctx, int *ctxlen, const char *lsm, char *new,
> + int newlen)
> +{
> + char *final;
> + size_t llen;
> +
> + llen = strlen(lsm) + 1;
> + /*
> + * A security module may or may not provide a trailing nul on
> + * when returning a security context. There is no definition
> + * of which it should be, and there are modules that do it
> + * each way.
> + */
> + newlen = strnlen(new, newlen) + 1;
> +
> + final = kzalloc(*ctxlen + llen + newlen, GFP_KERNEL);
> + if (final == NULL)
> + return -ENOMEM;
> + if (*ctxlen)
> + memcpy(final, *ctx, *ctxlen);
> + memcpy(final + *ctxlen, lsm, llen);
> + memcpy(final + *ctxlen + llen, new, newlen);
if @new doesn't have a newline appended at its end this will read 1 byte
passed the end of the @new buffer. Nor will the result have a trailing
\0 as expected unless we get lucky.
@new will never have a newline at the end. The trailing nul comes
from the allocation being done with kzalloc(). This function has to
be considered in the context of its caller.
> + kfree(*ctx);
> + *ctx = final;
> + *ctxlen = *ctxlen + llen + newlen;
> + return 0;
> +}
> +
> /*
> * The default value of the LSM hook is defined in linux/lsm_hook_defs.h and
> * can be accessed with:
> @@ -2124,6 +2166,10 @@ int security_getprocattr(struct task_struct *p, const char
*lsm, char *name,
> char **value)
> {
> struct security_hook_list *hp;
> + char *final = NULL;
> + char *cp;
> + int rc = 0;
> + int finallen = 0;
these are only used by context so they could be moved under its if, this
is really just a style comment and I'll leave it up to you
Old coding habits die hard. Unless there's value to gain, I'll leave it
as is.
> int display = lsm_task_display(current);
> int slot = 0;
>
> @@ -2151,6 +2197,30 @@ int security_getprocattr(struct task_struct *p, const char
*lsm, char *name,
> return -ENOMEM;
> }
>
> + if (!strcmp(name, "context")) {
> + hlist_for_each_entry(hp, &security_hook_heads.getprocattr,
> + list) {
> + rc = hp->hook.getprocattr(p, "context", &cp);
> + if (rc == -EINVAL)
> + continue;
> + if (rc < 0) {
> + kfree(final);
> + return rc;
> + }
> + rc = append_ctx(&final, &finallen, hp->lsmid->lsm,
> + cp, rc);
> + kfree(cp);
> + if (rc < 0) {
> + kfree(final);
> + return rc;
> + }
> + }
> + if (final == NULL)
> + return -EINVAL;
> + *value = final;
> + return finallen;
> + }
> +
> hlist_for_each_entry(hp, &security_hook_heads.getprocattr, list) {
> if (lsm != NULL && strcmp(lsm, hp->lsmid->lsm))
> continue;
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index c13c207c5da1..43d5c09b9a9e 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -6288,7 +6288,7 @@ static int selinux_getprocattr(struct task_struct *p,
> goto bad;
> }
>
> - if (!strcmp(name, "current"))
> + if (!strcmp(name, "current") || !strcmp(name, "context"))
> sid = __tsec->sid;
> else if (!strcmp(name, "prev"))
> sid = __tsec->osid;
> diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
> index 6f0cdb40addc..d7bb6442f192 100644
> --- a/security/smack/smack_lsm.c
> +++ b/security/smack/smack_lsm.c
> @@ -3463,7 +3463,7 @@ static int smack_getprocattr(struct task_struct *p, char *name,
char **value)
> char *cp;
> int slen;
>
> - if (strcmp(name, "current") != 0)
> + if (strcmp(name, "current") != 0 && strcmp(name,
"context") != 0)
> return -EINVAL;
>
> cp = kstrdup(skp->smk_known, GFP_KERNEL);
>