From: Stephen Smalley <sds@tycho.nsa.gov>
To: Ondrej Mosnacek <omosnace@redhat.com>,
selinux@vger.kernel.org, Paul Moore <paul@paul-moore.com>
Cc: Milos Malik <mmalik@redhat.com>
Subject: Re: [PATCH] selinux: fix context string corruption in convert_context()
Date: Thu, 3 Oct 2019 12:52:47 -0400 [thread overview]
Message-ID: <384722fe-a040-15c6-933b-1e2cf091b203@tycho.nsa.gov> (raw)
In-Reply-To: <20191003135922.29498-1-omosnace@redhat.com>
On 10/3/19 9:59 AM, Ondrej Mosnacek wrote:
> string_to_context_struct() may garble the context string, so we need to
> copy back the contents again from the old context struct to avoid
> storing the corrupted context.
>
> Since string_to_context_struct() tokenizes (and therefore truncates) the
> context string and we are later potentially copying it with kstrdup(),
> this may eventually cause pieces of uninitialized kernel memory to be
> disclosed to userspace (when copying to userspace based on the stored
> length and not the null character).
>
> How to reproduce on Fedora and similar:
> # dnf install -y memcached
> # systemctl start memcached
> # semodule -d memcached
> # load_policy
> # load_policy
> # systemctl stop memcached
> # ausearch -m AVC
> type=AVC msg=audit(1570090572.648:313): avc: denied { signal } for pid=1 comm="systemd" scontext=system_u:system_r:init_t:s0 tcontext=system_u:object_r:unlabeled_t:s0 tclass=process permissive=0 trawcon=73797374656D5F75007400000000000070BE6E847296FFFF726F6D000096FFFF76
>
> Reported-by: Milos Malik <mmalik@redhat.com>
> Fixes: ee1a84fdfeed ("selinux: overhaul sidtab to fix bug and improve performance")
> Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
Acked-by: Stephen Smalley <sds@tycho.nsa.gov>
> ---
> security/selinux/ss/services.c | 9 ++++++++-
> 1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c
> index 3a29e7c24ba9..a5813c7629c1 100644
> --- a/security/selinux/ss/services.c
> +++ b/security/selinux/ss/services.c
> @@ -1946,7 +1946,14 @@ static int convert_context(struct context *oldc, struct context *newc, void *p)
> rc = string_to_context_struct(args->newp, NULL, s,
> newc, SECSID_NULL);
> if (rc == -EINVAL) {
> - /* Retain string representation for later mapping. */
> + /*
> + * Retain string representation for later mapping.
> + *
> + * IMPORTANT: We need to copy the contents of oldc->str
> + * back into s again because string_to_context_struct()
> + * may have garbled it.
> + */
> + memcpy(s, oldc->str, oldc->len);
> context_init(newc);
> newc->str = s;
> newc->len = oldc->len;
>
next prev parent reply other threads:[~2019-10-03 16:54 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-03 13:59 [PATCH] selinux: fix context string corruption in convert_context() Ondrej Mosnacek
2019-10-03 16:52 ` Stephen Smalley [this message]
2019-10-03 18:54 ` Paul Moore
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