Messages in this thread |  | | From | Alexander Shishkin <> | Subject | Re: [PATCH] stm class: fix a missing-check bug | Date | Wed, 03 Oct 2018 10:56:40 +0300 |
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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.
> 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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