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SubjectRe: [PATCH] selinux: stricter parsing in mls_context_to_sid()
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On 08/03/2018 05:36 AM, Jann Horn wrote:
> mls_context_to_sid incorrectly accepted MLS context strings that are
> followed by a dash and trailing garbage.
>
> Before this change, the following command works:
>
> # mount -t tmpfs -o 'context=system_u:object_r:tmp_t:s0-s0:c0-BLAH' \
> none mount
>
> After this change, it fails with the following error message in dmesg:
>
> SELinux: security_context_str_to_sid(system_u:object_r:tmp_t:s0-s0:c0-BLAH)
> failed for (dev tmpfs, type tmpfs) errno=-22
>
> This is not an important bug; but it is a small quirk that was useful for
> exploiting a vulnerability in fusermount.
>
> This patch does not change the behavior when the policy does not have MLS
> enabled.
>
> Signed-off-by: Jann Horn <jannh@google.com>

Acked-by: Stephen Smalley <sds@tycho.nsa.gov>

> ---
> security/selinux/ss/mls.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/security/selinux/ss/mls.c b/security/selinux/ss/mls.c
> index 39475fb455bc..2c73d612d2ee 100644
> --- a/security/selinux/ss/mls.c
> +++ b/security/selinux/ss/mls.c
> @@ -344,7 +344,7 @@ int mls_context_to_sid(struct policydb *pol,
> break;
> }
> }
> - if (delim == '-') {
> + if (delim == '-' && l == 0) {
> /* Extract high sensitivity. */
> scontextp = p;
> while (*p && *p != ':')
>

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