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SubjectRe: [PATCH 06b/26] Security: Make NFSD work with detached security
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On Thu, Jan 17, 2008 at 05:17:20PM +0000, David Howells wrote:
>
> Make NFSD work with detached security, using the patches that excise the
> security information from task_struct to struct task_security as a base.
>
> Each time NFSD wants a new security descriptor (to do NFS4 recovery or just to
> do NFS operations), a task_security record is derived from NFSD's *objective*
> security, modified and then applied as the *subjective* security. This means
> (a) the changes are not visible to anyone looking at NFSD through /proc, (b)
> there is no leakage between two consecutive ops with different security
> configurations.
>
> Consideration should probably be given to caching the task_security record on
> the basis that there'll probably be several ops that will want to use any
> particular security configuration.

Just curious--why? Are get_kernel_security(), etc., particularly
expensive?

--b.

>
> Furthermore, nfs4recover.c perhaps ought to set an appropriate LSM context on
> the record pointed to by rec_security so that the disk is accessed
> appropriately (see set_security_override[_from_ctx]()).
>
> NOTE! This patch must be and will be rolled in to patch 06 of 26 to make the
> latter compile fully, however it may be useful to the nfsd maintainers to see
> it as a separate patch.
>
> Signed-off-by: David Howells <dhowells@redhat.com>
> ---
>
> fs/nfsd/auth.c | 31 +++++++++++++++++-------
> fs/nfsd/nfs4recover.c | 64 +++++++++++++++++++++++++++++++------------------
> include/linux/sched.h | 1 +
> kernel/sys.c | 27 ++++++++++++++++++---
> 4 files changed, 86 insertions(+), 37 deletions(-)
>
>
> diff --git a/fs/nfsd/auth.c b/fs/nfsd/auth.c
> index 2192805..462d989 100644
> --- a/fs/nfsd/auth.c
> +++ b/fs/nfsd/auth.c
> @@ -6,6 +6,7 @@
>
> #include <linux/types.h>
> #include <linux/sched.h>
> +#include <linux/cred.h>
> #include <linux/sunrpc/svc.h>
> #include <linux/sunrpc/svcauth.h>
> #include <linux/nfsd/nfsd.h>
> @@ -28,11 +29,17 @@ int nfsexp_flags(struct svc_rqst *rqstp, struct svc_export *exp)
>
> int nfsd_setuser(struct svc_rqst *rqstp, struct svc_export *exp)
> {
> + struct task_security *sec, *old;
> struct svc_cred cred = rqstp->rq_cred;
> int i;
> int flags = nfsexp_flags(rqstp, exp);
> int ret;
>
> + /* derive the new security record from nfsd's objective security */
> + sec = get_kernel_security(current);
> + if (!sec)
> + return -ENOMEM;
> +
> if (flags & NFSEXP_ALLSQUASH) {
> cred.cr_uid = exp->ex_anon_uid;
> cred.cr_gid = exp->ex_anon_gid;
> @@ -56,23 +63,29 @@ int nfsd_setuser(struct svc_rqst *rqstp, struct svc_export *exp)
> get_group_info(cred.cr_group_info);
>
> if (cred.cr_uid != (uid_t) -1)
> - current->fsuid = cred.cr_uid;
> + sec->fsuid = cred.cr_uid;
> else
> - current->fsuid = exp->ex_anon_uid;
> + sec->fsuid = exp->ex_anon_uid;
> if (cred.cr_gid != (gid_t) -1)
> - current->fsgid = cred.cr_gid;
> + sec->fsgid = cred.cr_gid;
> else
> - current->fsgid = exp->ex_anon_gid;
> + sec->fsgid = exp->ex_anon_gid;
>
> - if (!cred.cr_group_info)
> + if (!cred.cr_group_info) {
> + put_task_security(sec);
> return -ENOMEM;
> - ret = set_current_groups(cred.cr_group_info);
> + }
> + ret = set_groups(sec, cred.cr_group_info);
> put_group_info(cred.cr_group_info);
> if ((cred.cr_uid)) {
> - cap_t(current->cap_effective) &= ~CAP_NFSD_MASK;
> + cap_t(sec->cap_effective) &= ~CAP_NFSD_MASK;
> } else {
> - cap_t(current->cap_effective) |= (CAP_NFSD_MASK &
> - current->cap_permitted);
> + cap_t(sec->cap_effective) |= CAP_NFSD_MASK & sec->cap_permitted;
> }
> +
> + /* set the new security as nfsd's subjective security */
> + old = current->act_as;
> + current->act_as = sec;
> + put_task_security(old);
> return ret;
> }
> diff --git a/fs/nfsd/nfs4recover.c b/fs/nfsd/nfs4recover.c
> index 1602cd0..ae91262 100644
> --- a/fs/nfsd/nfs4recover.c
> +++ b/fs/nfsd/nfs4recover.c
> @@ -46,27 +46,37 @@
> #include <linux/scatterlist.h>
> #include <linux/crypto.h>
> #include <linux/sched.h>
> +#include <linux/cred.h>
>
> #define NFSDDBG_FACILITY NFSDDBG_PROC
>
> /* Globals */
> static struct nameidata rec_dir;
> static int rec_dir_init = 0;
> +static struct task_security *rec_security;
>
> +/*
> + * switch the special recovery access security in on the current task's
> + * subjective security
> + */
> static void
> -nfs4_save_user(uid_t *saveuid, gid_t *savegid)
> +nfs4_begin_secure(struct task_security **saved_sec)
> {
> - *saveuid = current->fsuid;
> - *savegid = current->fsgid;
> - current->fsuid = 0;
> - current->fsgid = 0;
> + *saved_sec = current->act_as;
> + current->act_as = get_task_security(rec_security);
> }
>
> +/*
> + * return the current task's subjective security to its former glory
> + */
> static void
> -nfs4_reset_user(uid_t saveuid, gid_t savegid)
> +nfs4_end_secure(struct task_security *saved_sec)
> {
> - current->fsuid = saveuid;
> - current->fsgid = savegid;
> + struct task_security *discard;
> +
> + discard = current->act_as;
> + current->act_as = saved_sec;
> + put_task_security(discard);
> }
>
> static void
> @@ -128,10 +138,9 @@ nfsd4_sync_rec_dir(void)
> int
> nfsd4_create_clid_dir(struct nfs4_client *clp)
> {
> + struct task_security *saved_sec;
> char *dname = clp->cl_recdir;
> struct dentry *dentry;
> - uid_t uid;
> - gid_t gid;
> int status;
>
> dprintk("NFSD: nfsd4_create_clid_dir for \"%s\"\n", dname);
> @@ -139,7 +148,7 @@ nfsd4_create_clid_dir(struct nfs4_client *clp)
> if (!rec_dir_init || clp->cl_firststate)
> return 0;
>
> - nfs4_save_user(&uid, &gid);
> + nfs4_begin_secure(&saved_sec);
>
> /* lock the parent */
> mutex_lock(&rec_dir.dentry->d_inode->i_mutex);
> @@ -163,7 +172,7 @@ out_unlock:
> clp->cl_firststate = 1;
> nfsd4_sync_rec_dir();
> }
> - nfs4_reset_user(uid, gid);
> + nfs4_end_secure(saved_sec);
> dprintk("NFSD: nfsd4_create_clid_dir returns %d\n", status);
> return status;
> }
> @@ -206,20 +215,19 @@ nfsd4_build_dentrylist(void *arg, const char *name, int namlen,
> static int
> nfsd4_list_rec_dir(struct dentry *dir, recdir_func *f)
> {
> + struct task_security *saved_sec;
> struct file *filp;
> struct dentry_list_arg dla = {
> .parent = dir,
> };
> struct list_head *dentries = &dla.dentries;
> struct dentry_list *child;
> - uid_t uid;
> - gid_t gid;
> int status;
>
> if (!rec_dir_init)
> return 0;
>
> - nfs4_save_user(&uid, &gid);
> + nfs4_begin_secure(&saved_sec);
>
> filp = dentry_open(dget(dir), mntget(rec_dir.mnt), O_RDONLY);
> status = PTR_ERR(filp);
> @@ -244,7 +252,7 @@ out:
> dput(child->dentry);
> kfree(child);
> }
> - nfs4_reset_user(uid, gid);
> + nfs4_end_secure(saved_sec);
> return status;
> }
>
> @@ -306,17 +314,16 @@ out:
> void
> nfsd4_remove_clid_dir(struct nfs4_client *clp)
> {
> - uid_t uid;
> - gid_t gid;
> + struct task_security *saved_sec;
> int status;
>
> if (!rec_dir_init || !clp->cl_firststate)
> return;
>
> clp->cl_firststate = 0;
> - nfs4_save_user(&uid, &gid);
> + nfs4_begin_secure(&saved_sec);
> status = nfsd4_unlink_clid_dir(clp->cl_recdir, HEXDIR_LEN-1);
> - nfs4_reset_user(uid, gid);
> + nfs4_end_secure(saved_sec);
> if (status == 0)
> nfsd4_sync_rec_dir();
> if (status)
> @@ -387,8 +394,7 @@ nfsd4_recdir_load(void) {
> void
> nfsd4_init_recdir(char *rec_dirname)
> {
> - uid_t uid = 0;
> - gid_t gid = 0;
> + struct task_security *saved_sec;
> int status;
>
> printk("NFSD: Using %s as the NFSv4 state recovery directory\n",
> @@ -396,7 +402,15 @@ nfsd4_init_recdir(char *rec_dirname)
>
> BUG_ON(rec_dir_init);
>
> - nfs4_save_user(&uid, &gid);
> + /* derive the security record from this task's objective security */
> + rec_security = get_kernel_security(current);
> + if (!rec_security) {
> + printk("NFSD:"
> + " unable to allocate recovery directory security\n");
> + return;
> + }
> +
> + nfs4_begin_secure(&saved_sec);
>
> status = path_lookup(rec_dirname, LOOKUP_FOLLOW | LOOKUP_DIRECTORY,
> &rec_dir);
> @@ -406,7 +420,8 @@ nfsd4_init_recdir(char *rec_dirname)
>
> if (!status)
> rec_dir_init = 1;
> - nfs4_reset_user(uid, gid);
> +
> + nfs4_end_secure(saved_sec);
> }
>
> void
> @@ -416,4 +431,5 @@ nfsd4_shutdown_recdir(void)
> return;
> rec_dir_init = 0;
> path_release(&rec_dir);
> + put_task_security(rec_security);
> }
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 697e707..d079b85 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -886,6 +886,7 @@ struct group_info {
> extern struct group_info *groups_alloc(int gidsetsize);
> extern void groups_free(struct group_info *group_info);
> extern int set_current_groups(struct group_info *group_info);
> +extern int set_groups(struct task_security *sec, struct group_info *group_info);
> extern int groups_search(struct group_info *group_info, gid_t grp);
> /* access the groups "array" with this macro */
> #define GROUP_AT(gi, i) \
> diff --git a/kernel/sys.c b/kernel/sys.c
> index e331b6f..790639f 100644
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -1245,10 +1245,16 @@ int groups_search(struct group_info *group_info, gid_t grp)
> return 0;
> }
>
> -/* validate and set current->group_info */
> -int set_current_groups(struct group_info *group_info)
> +/**
> + * set_groups - Change a group subscription in a security record
> + * @sec: The security record to alter
> + * @group_info: The group list to impose
> + *
> + * Validate a group subscription and, if valid, impose it upon a task security
> + * record.
> + */
> +int set_groups(struct task_security *sec, struct group_info *group_info)
> {
> - struct task_security *sec = current->sec;
> int retval;
> struct group_info *old_info;
>
> @@ -1265,10 +1271,23 @@ int set_current_groups(struct group_info *group_info)
> spin_unlock(&sec->lock);
>
> put_group_info(old_info);
> -
> return 0;
> }
>
> +EXPORT_SYMBOL(set_groups);
> +
> +/**
> + * set_current_groups - Change current's group subscription
> + * @group_info: The group list to impose
> + *
> + * Validate a group subscription and, if valid, impose it upon current's task
> + * security record.
> + */
> +int set_current_groups(struct group_info *group_info)
> +{
> + return set_groups(current->sec, group_info);
> +}
> +
> EXPORT_SYMBOL(set_current_groups);
>
> asmlinkage long sys_getgroups(int gidsetsize, gid_t __user *grouplist)


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