Messages in this thread |  | | From | Wenwen Wang <> | Date | Wed, 3 Oct 2018 09:54:34 -0500 | Subject | Re: [PATCH] stm class: fix a missing-check bug |
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On Wed, Oct 3, 2018 at 2:57 AM Alexander Shishkin <alexander.shishkin@linux.intel.com> wrote: > > Wenwen Wang <wang6495@umn.edu> writes: > > > In stm_char_policy_set_ioctl(), the 'size' field of the struct > > 'stp_polic_id' is firstly copied from the user space and then checked, > > because the length of the 'id' field in this struct, which represents an > > identification string, is not fixed. If the 'size' field cannot pass the > > check, an error code EINVAL will be returned. However, after the check, the > > whole struct is copied again from the user space. Given that the user data > > resides in the user space, a malicious user-space process can race to > > change the size between the two copies. By doing so, the attacker can > > bypass the check on the 'size' field and inject malicious data. > > How? The id->size is not used for anything. > > And even if there was a problem, this: > > > - if (copy_from_user(id, arg, size)) { > > + if (copy_from_user(&id->master, (char __user *)arg + sizeof(size), > > + size - sizeof(size))) { > > is completely pointless.
Given that id->size is not used, it should not be copied from the user space. This code is used to remove such redundant copy.
> > > ret = -EFAULT; > > goto err_free; > > } > > > > + id->size = size; > > So, if we did use id->size after the copying, we'd indeed have this line > in the code. But since we don't, it's also pointless, so it's not there. > > Thanks, > -- > Alex
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