linux-kernel - Re: [PATCH v3 1/5] LSM: Ensure the correct LSM context releaser

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Message-ID: <3db0da6b-4c09-43e6-a75c-c38353e191b3@schaufler-ca.com>
Date: Fri, 6 Dec 2024 12:57:52 -0800
From: Casey Schaufler <casey@...aufler-ca.com>
To: Kees Bakker <kees@...erbout.nl>, paul@...l-moore.com,
 linux-security-module@...r.kernel.org
Cc: jmorris@...ei.org, serge@...lyn.com, keescook@...omium.org,
 john.johansen@...onical.com, penguin-kernel@...ove.sakura.ne.jp,
 stephen.smalley.work@...il.com, linux-kernel@...r.kernel.org,
 selinux@...r.kernel.org, mic@...ikod.net, linux-integrity@...r.kernel.org,
 netdev@...r.kernel.org, audit@...r.kernel.org,
 netfilter-devel@...r.kernel.org, linux-nfs@...r.kernel.org,
 Todd Kjos <tkjos@...gle.com>, Casey Schaufler <casey@...aufler-ca.com>
Subject: Re: [PATCH v3 1/5] LSM: Ensure the correct LSM context releaser

On 12/6/2024 12:05 PM, Kees Bakker wrote:
> Op 23-10-2024 om 23:21 schreef Casey Schaufler:
>> Add a new lsm_context data structure to hold all the information about a
>> "security context", including the string, its size and which LSM
>> allocated
>> the string. The allocation information is necessary because LSMs have
>> different policies regarding the lifecycle of these strings. SELinux
>> allocates and destroys them on each use, whereas Smack provides a
>> pointer
>> to an entry in a list that never goes away.
>>
>> Update security_release_secctx() to use the lsm_context instead of a
>> (char *, len) pair. Change its callers to do likewise.  The LSMs
>> supporting this hook have had comments added to remind the developer
>> that there is more work to be done.
>>
>> The BPF security module provides all LSM hooks. While there has yet to
>> be a known instance of a BPF configuration that uses security contexts,
>> the possibility is real. In the existing implementation there is
>> potential for multiple frees in that case.
>>
>> Signed-off-by: Casey Schaufler <casey@...aufler-ca.com>
>> Cc: linux-integrity@...r.kernel.org
>> Cc: netdev@...r.kernel.org
>> Cc: audit@...r.kernel.org
>> Cc: netfilter-devel@...r.kernel.org
>> To: Pablo Neira Ayuso <pablo@...filter.org>
>> Cc: linux-nfs@...r.kernel.org
>> Cc: Todd Kjos <tkjos@...gle.com>
>> ---
>>   drivers/android/binder.c                | 24 +++++++--------
>>   fs/ceph/xattr.c                         |  6 +++-
>>   fs/nfs/nfs4proc.c                       |  8 +++--
>>   fs/nfsd/nfs4xdr.c                       |  8 +++--
>>   include/linux/lsm_hook_defs.h           |  2 +-
>>   include/linux/security.h                | 35 ++++++++++++++++++++--
>>   include/net/scm.h                       | 11 +++----
>>   kernel/audit.c                          | 30 +++++++++----------
>>   kernel/auditsc.c                        | 23 +++++++-------
>>   net/ipv4/ip_sockglue.c                  | 10 +++----
>>   net/netfilter/nf_conntrack_netlink.c    | 10 +++----
>>   net/netfilter/nf_conntrack_standalone.c |  9 +++---
>>   net/netfilter/nfnetlink_queue.c         | 13 +++++---
>>   net/netlabel/netlabel_unlabeled.c       | 40 +++++++++++--------------
>>   net/netlabel/netlabel_user.c            | 11 ++++---
>>   security/apparmor/include/secid.h       |  2 +-
>>   security/apparmor/secid.c               | 11 +++++--
>>   security/security.c                     |  8 ++---
>>   security/selinux/hooks.c                | 11 +++++--
>>   19 files changed, 165 insertions(+), 107 deletions(-)
>>
>> diff --git a/drivers/android/binder.c b/drivers/android/binder.c
>> index 978740537a1a..d4229bf6f789 100644
>> --- a/drivers/android/binder.c
>> +++ b/drivers/android/binder.c
>> @@ -3011,8 +3011,7 @@ static void binder_transaction(struct
>> binder_proc *proc,
>>       struct binder_context *context = proc->context;
>>       int t_debug_id = atomic_inc_return(&binder_last_id);
>>       ktime_t t_start_time = ktime_get();
>> -    char *secctx = NULL;
>> -    u32 secctx_sz = 0;
>> +    struct lsm_context lsmctx;
> Not initialized ?

Thank you for the review.
It makes sense to initialize it here. I will make the change.

>>       struct list_head sgc_head;
>>       struct list_head pf_head;
>>       const void __user *user_buffer = (const void __user *)
>> @@ -3291,7 +3290,8 @@ static void binder_transaction(struct
>> binder_proc *proc,
>>           size_t added_size;
>>             security_cred_getsecid(proc->cred, &secid);
>> -        ret = security_secid_to_secctx(secid, &secctx, &secctx_sz);
>> +        ret = security_secid_to_secctx(secid, &lsmctx.context,
>> +                           &lsmctx.len);
>>           if (ret) {
>>               binder_txn_error("%d:%d failed to get security context\n",
>>                   thread->pid, proc->pid);
>> @@ -3300,7 +3300,7 @@ static void binder_transaction(struct
>> binder_proc *proc,
>>               return_error_line = __LINE__;
>>               goto err_get_secctx_failed;
>>           }
>> -        added_size = ALIGN(secctx_sz, sizeof(u64));
>> +        added_size = ALIGN(lsmctx.len, sizeof(u64));
>>           extra_buffers_size += added_size;
>>           if (extra_buffers_size < added_size) {
>>               binder_txn_error("%d:%d integer overflow of
>> extra_buffers_size\n",
>> @@ -3334,23 +3334,23 @@ static void binder_transaction(struct
>> binder_proc *proc,
>>           t->buffer = NULL;
>>           goto err_binder_alloc_buf_failed;
>>       }
>> -    if (secctx) {
>> +    if (lsmctx.context) {
> From code inspection it is not immediately obvious. Can you
> guarantee that lsmctx is always initialized when the code
> gets to this point? Perhaps it is safer to just initialize when
> it is defined above (line 3014).
>
>