| From | David Howells <> | Subject | Re: [PATCH 29/38] vfs: syscall: Add fsconfig() for configuring and managing a context [ver #10] | Date | Sun, 29 Jul 2018 09:50:00 +0100 |
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Jann Horn <jannh@google.com> wrote:
> [...] > > + case fsconfig_set_binary: > > + param.type = fs_value_is_blob; > > + param.size = aux; > > + param.blob = memdup_user_nul(_value, aux); > > + if (IS_ERR(param.blob)) { > > + ret = PTR_ERR(param.blob); > > + goto out_key; > > + } > > + break; > > This means that a namespace admin (iow, an unprivileged user) can > allocate 1MB of unswappable kmalloc memory per userspace task, right? > Using userfaultfd or FUSE, you can then stall the task as long as you > want while it has that allocation. Is that problematic, or is that > normal?
That's not exactly the case. A userspace task can make a temporary allocation, but unless the filesystem grabs it, it's released again on exit from the system call.
Note that I should probably use vmalloc() rather than kmalloc(), but that doesn't really affect your point. I could also pass the user pointer through to the filesystem instead - I wanted to avoid that for this interface, but it make sense in this instance.
David
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