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Message-ID: <4263259c-7fc4-58e4-a86d-7ba92abe510a@schaufler-ca.com>
Date: Fri, 24 Jun 2016 13:05:14 -0700
From: Casey Schaufler <casey@...aufler-ca.com>
To: Paul Moore <paul@...l-moore.com>
Cc: LSM <linux-security-module@...r.kernel.org>,
James Morris <jmorris@...ei.org>,
John Johansen <john.johansen@...onical.com>,
Stephen Smalley <sds@...ho.nsa.gov>,
Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
Kees Cook <keescook@...omium.org>,
LKLM <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 2/3] LSM: module hierarchy in /proc/.../attr
On 6/24/2016 12:11 PM, Paul Moore wrote:
> On Thu, Jun 23, 2016 at 5:11 PM, Casey Schaufler <casey@...aufler-ca.com> wrote:
>> Subject: [PATCH v4 2/3] LSM: module hierarchy in /proc/.../attr
>>
>> Back in 2007 I made what turned out to be a rather serious
>> mistake in the implementation of the Smack security module.
>> The SELinux module used an interface in /proc to manipulate
>> the security context on processes. Rather than use a similar
>> interface, I used the same interface. The AppArmor team did
>> likewise. Now /proc/.../attr/current will tell you the
>> security "context" of the process, but it will be different
>> depending on the security module you're using. That hasn't
>> been a problem to date, as you can only have one module
>> that supports process attributes at a time. We are coming
>> up on a change to that, where multiple modules with process
>> attributes can be supported. (Not included here)
>>
>> This patch provides a subdirectory in /proc/.../attr for
>> each of the security modules that use the LSM hooks
>> getprocattr() and setprocattr(). Each of the interfaces
>> used by a module are presented in the subdirectory. The
>> old interfaces remain and work the same as before.
>> User space code can begin migrating to the subdirectory
>> interfaces in anticipation of the time when what comes
>> from /proc/self/attr/current might not be what a runtime
>> wants.
>>
>> The original implementation is by Kees Cook. The code
>> has been changed a bit to reflect changes in the direction
>> of the multiple concurrent module work, to be independent
>> of it, and to bring it up to date with the current tree.
>>
>> Signed-off-by: Casey Schaufler <casey@...aufler-ca.com>
>>
>> ---
>> Documentation/security/LSM.txt | 26 +++++++++---
>> fs/proc/base.c | 91 +++++++++++++++++++++++++++++++++++++-----
>> fs/proc/internal.h | 1 +
>> include/linux/security.h | 15 ++++---
>> security/security.c | 31 ++++++++++++--
>> 5 files changed, 140 insertions(+), 24 deletions(-)
>>
>> diff --git a/Documentation/security/LSM.txt b/Documentation/security/LSM.txt
>> index 3db7e67..125c489 100644
>> --- a/Documentation/security/LSM.txt
>> +++ b/Documentation/security/LSM.txt
>> @@ -16,11 +16,25 @@ MAC extensions, other extensions can be built using the LSM to provide
>> specific changes to system operation when these tweaks are not available
>> in the core functionality of Linux itself.
>>
>> -Without a specific LSM built into the kernel, the default LSM will be the
>> -Linux capabilities system. Most LSMs choose to extend the capabilities
>> -system, building their checks on top of the defined capability hooks.
>> -For more details on capabilities, see capabilities(7) in the Linux
>> -man-pages project.
>> +The Linux capabilities modules will always be included. For more details
>> +on capabilities, see capabilities(7) in the Linux man-pages project.
>> +This may be followed by any number of "minor" modules and at most one
>> +"major" module.
>> +
>> +A list of the active security modules can be found by reading
>> +/sys/kernel/security/lsm. This is a comma separated list, and
>> +will always include the capability module. The list reflects the
>> +order in which checks are made. The capability module will always
>> +be first, followed by any "minor" modules (e.g. Yama) and then
>> +the one "major" module (e.g. SELinux) if there is one configured.
> I wouldn't respin it just for this, but it seems like the paragraph
> above should really be part of patch 1/3, yes?
Yes. I can fix that for v5.
>> +Process attributes associated with "ma
>> diff --git a/fs/proc/base.c b/fs/proc/base.c
>> index a11eb71..182bc28 100644
>> --- a/fs/proc/base.c
>> +++ b/fs/proc/base.c
>> @@ -131,9 +131,13 @@ struct pid_entry {
>> #define REG(NAME, MODE, fops) \
>> NOD(NAME, (S_IFREG|(MODE)), NULL, &fops, {})
>> #define ONE(NAME, MODE, show) \
>> - NOD(NAME, (S_IFREG|(MODE)), \
>> + NOD(NAME, (S_IFREG|(MODE)), \
>> NULL, &proc_single_file_operations, \
>> { .proc_show = show } )
>> +#define ATTR(LSM, NAME, MODE) \
>> + NOD(NAME, (S_IFREG|(MODE)), \
>> + NULL, &proc_pid_attr_operations, \
>> + { .lsm = LSM })
>>
>> /*
>> * Count the number of hardlinks for the pid_entry table, excluding the .
>> @@ -2433,7 +2437,7 @@ static ssize_t proc_pid_attr_read(struct file * file, char __user * buf,
>> if (!task)
>> return -ESRCH;
>>
>> - length = security_getprocattr(task,
>> + length = security_getprocattr(task, PROC_I(inode)->op.lsm,
>> (char*)file->f_path.dentry->d_name.name,
>> &p);
>> put_task_struct(task);
>> @@ -2473,7 +2477,7 @@ static ssize_t proc_pid_attr_write(struct file * file, const char __user * buf,
>> if (length < 0)
>> goto out_free;
>>
>> - length = security_setprocattr(task,
>> + length = security_setprocattr(task, PROC_I(inode)->op.lsm,
>> (char*)file->f_path.dentry->d_name.name,
>> page, count);
>> mutex_unlock(&task->signal->cred_guard_mutex);
>> @@ -2491,13 +2495,82 @@ static const struct file_operations proc_pid_attr_operations = {
>> .llseek = generic_file_llseek,
>> };
>>
>> +#define LSM_DIR_OPS(LSM) \
>> +static int proc_##LSM##_attr_dir_iterate(struct file *filp, \
>> + struct dir_context *ctx) \
>> +{ \
>> + return proc_pident_readdir(filp, ctx, \
>> + LSM##_attr_dir_stuff, \
>> + ARRAY_SIZE(LSM##_attr_dir_stuff)); \
>> +} \
>> +\
>> +static const struct file_operations proc_##LSM##_attr_dir_ops = { \
>> + .read = generic_read_dir, \
>> + .iterate = proc_##LSM##_attr_dir_iterate, \
>> + .llseek = default_llseek, \
>> +}; \
>> +\
>> +static struct dentry *proc_##LSM##_attr_dir_lookup(struct inode *dir, \
>> + struct dentry *dentry, unsigned int flags) \
>> +{ \
>> + return proc_pident_lookup(dir, dentry, \
>> + LSM##_attr_dir_stuff, \
>> + ARRAY_SIZE(LSM##_attr_dir_stuff)); \
>> +} \
>> +\
>> +static const struct inode_operations proc_##LSM##_attr_dir_inode_ops = { \
>> + .lookup = proc_##LSM##_attr_dir_lookup, \
>> + .getattr = pid_getattr, \
>> + .setattr = proc_setattr, \
>> +}
>> +
>> +#ifdef CONFIG_SECURITY_SELINUX
>> +static const struct pid_entry selinux_attr_dir_stuff[] = {
>> + ATTR("selinux", "current", S_IRUGO|S_IWUGO),
>> + ATTR("selinux", "prev", S_IRUGO),
>> + ATTR("selinux", "exec", S_IRUGO|S_IWUGO),
>> + ATTR("selinux", "fscreate", S_IRUGO|S_IWUGO),
>> + ATTR("selinux", "keycreate", S_IRUGO|S_IWUGO),
>> + ATTR("selinux", "sockcreate", S_IRUGO|S_IWUGO),
>> +};
>> +LSM_DIR_OPS(selinux);
>> +#endif
>> +
>> +#ifdef CONFIG_SECURITY_SMACK
>> +static const struct pid_entry smack_attr_dir_stuff[] = {
>> + ATTR("smack", "current", S_IRUGO|S_IWUGO),
>> +};
>> +LSM_DIR_OPS(smack);
>> +#endif
>> +
>> +#ifdef CONFIG_SECURITY_APPARMOR
>> +static const struct pid_entry apparmor_attr_dir_stuff[] = {
>> + ATTR("apparmor", "current", S_IRUGO|S_IWUGO),
>> + ATTR("apparmor", "prev", S_IRUGO),
>> + ATTR("apparmor", "exec", S_IRUGO|S_IWUGO),
>> +};
>> +LSM_DIR_OPS(apparmor);
>> +#endif
>> +
>> static const struct pid_entry attr_dir_stuff[] = {
>> - REG("current", S_IRUGO|S_IWUGO, proc_pid_attr_operations),
>> - REG("prev", S_IRUGO, proc_pid_attr_operations),
>> - REG("exec", S_IRUGO|S_IWUGO, proc_pid_attr_operations),
>> - REG("fscreate", S_IRUGO|S_IWUGO, proc_pid_attr_operations),
>> - REG("keycreate", S_IRUGO|S_IWUGO, proc_pid_attr_operations),
>> - REG("sockcreate", S_IRUGO|S_IWUGO, proc_pid_attr_operations),
>> + ATTR(NULL, "current", S_IRUGO|S_IWUGO),
>> + ATTR(NULL, "prev", S_IRUGO),
>> + ATTR(NULL, "exec", S_IRUGO|S_IWUGO),
>> + ATTR(NULL, "fscreate", S_IRUGO|S_IWUGO),
>> + ATTR(NULL, "keycreate", S_IRUGO|S_IWUGO),
>> + ATTR(NULL, "sockcreate", S_IRUGO|S_IWUGO),
>> +#ifdef CONFIG_SECURITY_SELINUX
>> + DIR("selinux", S_IRUGO|S_IXUGO,
>> + proc_selinux_attr_dir_inode_ops, proc_selinux_attr_dir_ops),
>> +#endif
>> +#ifdef CONFIG_SECURITY_SMACK
>> + DIR("smack", S_IRUGO|S_IXUGO,
>> + proc_smack_attr_dir_inode_ops, proc_smack_attr_dir_ops),
>> +#endif
>> +#ifdef CONFIG_SECURITY_APPARMOR
>> + DIR("apparmor", S_IRUGO|S_IXUGO,
>> + proc_apparmor_attr_dir_inode_ops, proc_apparmor_attr_dir_ops),
>> +#endif
>> };
> With the number of LSMs set to grow, it seems like it might be a lot
> cleaner, and easier to maintain, if we moved the various LSM pid_entry
> definitions into the LSMs themselves. Granted, I say this without
> seriously looking at how one would do that, I'm just mentioning it
> here; it may prove to be more hassle than it is worth.
>
I have looked into doing it that way, but have yet to
come up with anything that would work. It seems like a
wonderful challenge for a young, nimble brain. Or maybe
an old wise one. In neither case, mine.
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