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SubjectRe: [PATCH 10/11] capsicum: prctl(2) to force use of O_BENEATH
Il 25/07/2014 15:47, David Drysdale ha scritto:
> @@ -1996,6 +2013,17 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
> if (arg2 || arg3 || arg4 || arg5)
> return -EINVAL;
> return current->no_new_privs ? 1 : 0;
> + case PR_SET_OPENAT_BENEATH:
> + if (arg2 != 1 || arg4 || arg5)
> + return -EINVAL;
> + if ((arg3 & ~(PR_SET_OPENAT_BENEATH_TSYNC)) != 0)
> + return -EINVAL;
> + error = prctl_set_openat_beneath(me, arg3);
> + break;
> + case PR_GET_OPENAT_BENEATH:
> + if (arg2 || arg3 || arg4 || arg5)
> + return -EINVAL;
> + return me->openat_beneath;
> case PR_GET_THP_DISABLE:
> if (arg2 || arg3 || arg4 || arg5)
> return -EINVAL;
>

Why are you always forbidding a change of prctl from 1 to 0? It should
be safe if current->no_new_privs is clear.

Do new threads inherit from the parent?

Also, I wonder if you need something like this check:

/*
* Installing a seccomp filter requires that the task has
* CAP_SYS_ADMIN in its namespace or be running with no_new_privs.
* This avoids scenarios where unprivileged tasks can affect the
* behavior of privileged children.
*/
if (!current->no_new_privs &&
security_capable_noaudit(current_cred(), current_user_ns(),
CAP_SYS_ADMIN) != 0)
return -EACCES;

Paolo


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