On 1/25/2022 2:18 PM, Paul Moore wrote:
On Tue, Oct 12, 2021 at 10:27 AM Casey Schaufler <casey@xxxxxxxxxxxxxxxx> wrote:
On 10/12/2021 3:32 AM, Christian Brauner wrote:
On Mon, Oct 11, 2021 at 03:40:22PM -0700, Casey Schaufler wrote:
The usual LSM hook "bail on fail" scheme doesn't work for cases where
a security module may return an error code indicating that it does not
recognize an input. In this particular case Smack sees a mount option
that it recognizes, and returns 0. A call to a BPF hook follows, which
returns -ENOPARAM, which confuses the caller because Smack has processed
its data.
Reported-by: syzbot+d1e3b1d92d25abf97943@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Casey Schaufler <casey@xxxxxxxxxxxxxxxx>
---
Thanks!
Note, I think that we still have the SELinux issue we discussed in the
other thread:
rc = selinux_add_opt(opt, param->string, &fc->security);
if (!rc) {
param->string = NULL;
rc = 1;
}
SELinux returns 1 not the expected 0. Not sure if that got fixed or is
queued-up for -next. In any case, this here seems correct independent of
that:
The aforementioned SELinux change depends on this patch. As the SELinux
code is today it blocks the problem seen with Smack, but introduces a
different issue. It prevents the BPF hook from being called.
So the question becomes whether the SELinux change should be included
here, or done separately. Without the security_fs_context_parse_param()
change the selinux_fs_context_parse_param() change results in messy
failures for SELinux mounts.
FWIW, this patch looks good to me, so:
Acked-by: Paul Moore <paul@xxxxxxxxxxxxxx>
... and with respect to the SELinux hook implementation returning 1 on
success, I don't have a good answer and looking through my inbox I see
David Howells hasn't responded either. I see nothing in the original
commit explaining why, so I'm going to say let's just change it to
zero and be done with it; the good news is that if we do it now we've
got almost a full cycle in linux-next to see what falls apart. As far
as the question of one vs two patches, it might be good to put both
changes into a single patch just so that folks who do backports don't
accidentally skip one and create a bad kernel build. Casey, did you
want to respin this patch or would you prefer me to submit another
version?
I can create a single patch. I tried the combination on Fedora
and it worked just fine. I'll rebase and resend.
Acked-by: Christian Brauner <christian.brauner@xxxxxxxxxx>
security/security.c | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)
diff --git a/security/security.c b/security/security.c
index 09533cbb7221..3cf0faaf1c5b 100644
--- a/security/security.c
+++ b/security/security.c
@@ -885,7 +885,19 @@ int security_fs_context_dup(struct fs_context *fc, struct fs_context *src_fc)
int security_fs_context_parse_param(struct fs_context *fc, struct fs_parameter *param)
{
- return call_int_hook(fs_context_parse_param, -ENOPARAM, fc, param);
+ struct security_hook_list *hp;
+ int trc;
+ int rc = -ENOPARAM;
+
+ hlist_for_each_entry(hp, &security_hook_heads.fs_context_parse_param,
+ list) {
+ trc = hp->hook.fs_context_parse_param(fc, param);
+ if (trc == 0)
+ rc = 0;
+ else if (trc != -ENOPARAM)
+ return trc;
+ }
+ return rc;
}
