Date:   Tue, 4 Feb 2020 16:01:20 +0100
From:   Ondrej Mosnacek <omosnace@...hat.com>
To:     Stephen Smalley <sds@...ho.nsa.gov>
Cc:     Lucas Stach <dev@...xeye.de>, Paul Moore <paul@...l-moore.com>,
        SElinux list <selinux@...r.kernel.org>,
        Linux kernel mailing list <linux-kernel@...r.kernel.org>,
        Richard Haines <richard_c_haines@...nternet.com>
Subject: Re: [PATCH RFC] selinux: policydb - convert filename trans hash to rhashtable

On Fri, Jan 17, 2020 at 8:11 PM Stephen Smalley <sds@...ho.nsa.gov> wrote:
> On 1/16/20 4:39 PM, Lucas Stach wrote:
> > The current hash is too small for current usages in, e.g. the Fedora standard
> > policy. On file creates a considerable amount of CPU time is spent walking the
> > the hash chains. Increasing the number of hash buckets somewhat mitigates the
> > issue, but doesn't completely get rid of the long hash chains.
> >
> > This patch does take the bit more invasive route by converting the filename
> > trans hash to a rhashtable to allow this hash to scale with load.
> >
> > fs_mark create benchmark on a SSD device, no ramdisk:
> > Count          Size       Files/sec     App Overhead
> > before:
> > 10000          512        512.3           147715
> > after:
> > 10000          512        572.3            75141
> >
> > filenametr_cmp(), which was the topmost function in the CPU cycle trace before
> > at ~5% of the overall CPU time, is now down in the noise.
>
> Thank you for working on this.  IMHO, Fedora overuses name-based type
> transitions but that's another topic. I haven't yet investigated the
> root cause but with your patch applied, I see some test failures related
> to name-based transitions:
>
> [...]
> #   Failed test at overlay/test line 439.
> overlay/test ................ 114/119 # Looks like you failed 1 test of 119.
> [...]
> filesystem/test ............. 3/70 File context error, expected:
>         test_filesystem_filenametranscon1_t
> got:
>         test_filesystem_filetranscon_t
>
> #   Failed test at filesystem/test line 279.
> File context error, expected:
>         test_filesystem_filenametranscon2_t
> got:
>         test_filesystem_filetranscon_t
>
> #   Failed test at filesystem/test line 286.
> filesystem/test ............. 68/70 # Looks like you failed 2 tests of 70.
>
> You can reproduce by cloning the selinux-testsuite from
> https://github.com/SELinuxProject/selinux-testsuite, applying the
> filesystem tests patch from
> https://patchwork.kernel.org/patch/11337659/,
> and following the README.md instructions.

I think I figured out what's wrong - see below.

>
> >
> > Signed-off-by: Lucas Stach <dev@...xeye.de>
> > ---
> >   security/selinux/ss/policydb.c | 140 +++++++++++++++++++++++----------
> >   security/selinux/ss/policydb.h |  14 ++--
> >   security/selinux/ss/services.c |  31 +-------
> >   3 files changed, 109 insertions(+), 76 deletions(-)
> >
> > diff --git a/security/selinux/ss/policydb.c b/security/selinux/ss/policydb.c
> > index e20624a68f5d..d059317c15b6 100644
> > --- a/security/selinux/ss/policydb.c
> > +++ b/security/selinux/ss/policydb.c
> > @@ -34,6 +34,7 @@
> >   #include <linux/string.h>
> >   #include <linux/errno.h>
> >   #include <linux/audit.h>
> > +#include <linux/rhashtable.h>
> >   #include "security.h"
> >
> >   #include "policydb.h"
> > @@ -334,15 +335,13 @@ static int (*destroy_f[SYM_NUM]) (void *key, void *datum, void *datap) =
> >       cat_destroy,
> >   };
> >
> > -static int filenametr_destroy(void *key, void *datum, void *p)
> > +static void filenametr_destroy(void *ptr, void *arg)
> >   {
> > -     struct filename_trans *ft = key;
> > +     struct filename_trans *ft = ptr;
> >
> >       kfree(ft->name);
> > -     kfree(key);
> > -     kfree(datum);
> > +     kfree(ft);
> >       cond_resched();
> > -     return 0;
> >   }
> >
> >   static int range_tr_destroy(void *key, void *datum, void *p)
> > @@ -404,9 +403,9 @@ static int roles_init(struct policydb *p)
> >       return rc;
> >   }
> >
> > -static u32 filenametr_hash(struct hashtab *h, const void *k)
> > +static u32 filenametr_hash(const void *data, u32 len, u32 seed)
> >   {
> > -     const struct filename_trans *ft = k;
> > +     const struct filename_trans *ft = data;
> >       unsigned long hash;
> >       unsigned int byte_num;
> >       unsigned char focus;
> > @@ -416,13 +415,15 @@ static u32 filenametr_hash(struct hashtab *h, const void *k)
> >       byte_num = 0;
> >       while ((focus = ft->name[byte_num++]))
> >               hash = partial_name_hash(focus, hash);
> > -     return hash & (h->size - 1);
> > +
> > +     return end_name_hash(hash);
> >   }
> >
> > -static int filenametr_cmp(struct hashtab *h, const void *k1, const void *k2)
> > +static int filenametr_cmp(struct rhashtable_compare_arg *arg,
> > +                       const void *obj)
> >   {
> > -     const struct filename_trans *ft1 = k1;
> > -     const struct filename_trans *ft2 = k2;
> > +     const struct filename_trans *ft1 = arg->key;
> > +     const struct filename_trans *ft2 = obj;
> >       int v;
> >
> >       v = ft1->stype - ft2->stype;
> > @@ -441,6 +442,39 @@ static int filenametr_cmp(struct hashtab *h, const void *k1, const void *k2)
> >
> >   }
> >
> > +static const struct rhashtable_params filename_trans_hashparams = {
> > +     .nelem_hint             = 1024,
> > +     .head_offset            = offsetof(struct filename_trans, hash_head),

You need to add:

+.hashfn = filenametr_hash,

here so that the key is correctly hashed on lookup. After applying
this fix, the selinux-testuite passes for me with this patch.

> > +     .obj_hashfn             = filenametr_hash,
> > +     .obj_cmpfn              = filenametr_cmp,
> > +};
> > +
> > +void policydb_filename_compute_type(struct policydb *policydb,
> > +                                 struct context *newcontext,
> > +                                 u32 stype, u32 ttype, u16 tclass,
> > +                                 const char *objname)
> > +{
> > +     struct filename_trans key, *ft;
> > +
> > +     /*
> > +      * Most filename trans rules are going to live in specific directories
> > +      * like /dev or /var/run.  This bitmap will quickly skip rule searches
> > +      * if the ttype does not contain any rules.
> > +      */
> > +     if (!ebitmap_get_bit(&policydb->filename_trans_ttypes, ttype))
> > +             return;
> > +
> > +     key.stype = stype;
> > +     key.ttype = ttype;
> > +     key.tclass = tclass;
> > +     key.name = objname;
> > +
> > +     ft = rhashtable_lookup(&policydb->filename_trans, &key,
> > +                            filename_trans_hashparams);
> > +     if (ft)
> > +             newcontext->type = ft->otype;
> > +}
> > +
> >   static u32 rangetr_hash(struct hashtab *h, const void *k)
> >   {
> >       const struct range_trans *key = k;
> > @@ -494,12 +528,7 @@ static int policydb_init(struct policydb *p)
> >       if (rc)
> >               goto out;
> >
> > -     p->filename_trans = hashtab_create(filenametr_hash, filenametr_cmp,
> > -                                        (1 << 10));
> > -     if (!p->filename_trans) {
> > -             rc = -ENOMEM;
> > -             goto out;
> > -     }
> > +     rhashtable_init(&p->filename_trans, &filename_trans_hashparams);
> >
> >       p->range_tr = hashtab_create(rangetr_hash, rangetr_cmp, 256);
> >       if (!p->range_tr) {
> > @@ -513,7 +542,7 @@ static int policydb_init(struct policydb *p)
> >
> >       return 0;
> >   out:
> > -     hashtab_destroy(p->filename_trans);
> > +     rhashtable_destroy(&p->filename_trans);
> >       hashtab_destroy(p->range_tr);
> >       for (i = 0; i < SYM_NUM; i++) {
> >               hashtab_map(p->symtab[i].table, destroy_f[i], NULL);
> > @@ -831,8 +860,8 @@ void policydb_destroy(struct policydb *p)
> >       }
> >       kfree(lra);
> >
> > -     hashtab_map(p->filename_trans, filenametr_destroy, NULL);
> > -     hashtab_destroy(p->filename_trans);
> > +     rhashtable_free_and_destroy(&p->filename_trans, filenametr_destroy,
> > +                                 NULL);
> >
> >       hashtab_map(p->range_tr, range_tr_destroy, NULL);
> >       hashtab_destroy(p->range_tr);
> > @@ -1878,7 +1907,6 @@ static int range_read(struct policydb *p, void *fp)
> >   static int filename_trans_read(struct policydb *p, void *fp)
> >   {
> >       struct filename_trans *ft;
> > -     struct filename_trans_datum *otype;
> >       char *name;
> >       u32 nel, len;
> >       __le32 buf[4];
> > @@ -1893,7 +1921,6 @@ static int filename_trans_read(struct policydb *p, void *fp)
> >       nel = le32_to_cpu(buf[0]);
> >
> >       for (i = 0; i < nel; i++) {
> > -             otype = NULL;
> >               name = NULL;
> >
> >               rc = -ENOMEM;
> > @@ -1901,11 +1928,6 @@ static int filename_trans_read(struct policydb *p, void *fp)
> >               if (!ft)
> >                       goto out;
> >
> > -             rc = -ENOMEM;
> > -             otype = kmalloc(sizeof(*otype), GFP_KERNEL);
> > -             if (!otype)
> > -                     goto out;
> > -
> >               /* length of the path component string */
> >               rc = next_entry(buf, fp, sizeof(u32));
> >               if (rc)
> > @@ -1926,14 +1948,14 @@ static int filename_trans_read(struct policydb *p, void *fp)
> >               ft->stype = le32_to_cpu(buf[0]);
> >               ft->ttype = le32_to_cpu(buf[1]);
> >               ft->tclass = le32_to_cpu(buf[2]);
> > -
> > -             otype->otype = le32_to_cpu(buf[3]);
> > +             ft->otype = le32_to_cpu(buf[3]);
> >
> >               rc = ebitmap_set_bit(&p->filename_trans_ttypes, ft->ttype, 1);
> >               if (rc)
> >                       goto out;
> >
> > -             rc = hashtab_insert(p->filename_trans, ft, otype);
> > +             rc = rhashtable_insert_fast(&p->filename_trans, &ft->hash_head,
> > +                                         filename_trans_hashparams);
> >               if (rc) {
> >                       /*
> >                        * Do not return -EEXIST to the caller, or the system
> > @@ -1944,15 +1966,12 @@ static int filename_trans_read(struct policydb *p, void *fp)
> >                       /* But free memory to avoid memory leak. */
> >                       kfree(ft);
> >                       kfree(name);
> > -                     kfree(otype);
> >               }
> >       }
> > -     hash_eval(p->filename_trans, "filenametr");
> >       return 0;
> >   out:
> >       kfree(ft);
> >       kfree(name);
> > -     kfree(otype);
> >
> >       return rc;
> >   }
> > @@ -3323,12 +3342,10 @@ static int range_write(struct policydb *p, void *fp)
> >       return 0;
> >   }
> >
> > -static int filename_write_helper(void *key, void *data, void *ptr)
> > +static int filename_write_helper(struct filename_trans *ft,
> > +                              struct policy_file *fp)
> >   {
> >       __le32 buf[4];
> > -     struct filename_trans *ft = key;
> > -     struct filename_trans_datum *otype = data;
> > -     void *fp = ptr;
> >       int rc;
> >       u32 len;
> >
> > @@ -3345,7 +3362,7 @@ static int filename_write_helper(void *key, void *data, void *ptr)
> >       buf[0] = cpu_to_le32(ft->stype);
> >       buf[1] = cpu_to_le32(ft->ttype);
> >       buf[2] = cpu_to_le32(ft->tclass);
> > -     buf[3] = cpu_to_le32(otype->otype);
> > +     buf[3] = cpu_to_le32(ft->otype);
> >
> >       rc = put_entry(buf, sizeof(u32), 4, fp);
> >       if (rc)
> > @@ -3356,15 +3373,34 @@ static int filename_write_helper(void *key, void *data, void *ptr)
> >
> >   static int filename_trans_write(struct policydb *p, void *fp)
> >   {
> > -     u32 nel;
> > +     u32 nel = 0;
> >       __le32 buf[1];
> > -     int rc;
> > +     int rc = 0;
> > +     struct rhashtable_iter iter;
> >
> >       if (p->policyvers < POLICYDB_VERSION_FILENAME_TRANS)
> >               return 0;
> >
> > -     nel = 0;
> > -     rc = hashtab_map(p->filename_trans, hashtab_cnt, &nel);
> > +     rhashtable_walk_enter(&p->filename_trans, &iter);
> > +     rhashtable_walk_start(&iter);
> > +     for(;;) {
> > +             struct filename_trans *trans;
> > +
> > +             trans = rhashtable_walk_next(&iter);
> > +             if (!trans)
> > +                     break;
> > +             if (IS_ERR(trans)) {
> > +                     if (PTR_ERR(trans) == -EAGAIN) {
> > +                             nel = 0;
> > +                             continue;
> > +                     }
> > +                     rc = PTR_ERR(trans);
> > +                     break;
> > +             }
> > +             nel++;
> > +     };
> > +     rhashtable_walk_stop(&iter);
> > +     rhashtable_walk_exit(&iter);
> >       if (rc)
> >               return rc;
> >
> > @@ -3373,7 +3409,25 @@ static int filename_trans_write(struct policydb *p, void *fp)
> >       if (rc)
> >               return rc;
> >
> > -     rc = hashtab_map(p->filename_trans, filename_write_helper, fp);
> > +     rhashtable_walk_enter(&p->filename_trans, &iter);
> > +     rhashtable_walk_start(&iter);
> > +     for(;;) {
> > +             struct filename_trans *trans;
> > +
> > +             trans = rhashtable_walk_next(&iter);
> > +             if (!trans)
> > +                     break;
> > +             if (IS_ERR(trans)) {
> > +                     if (PTR_ERR(trans) == -EAGAIN) {
> > +                             continue;
> > +                     }
> > +                     rc = PTR_ERR(trans);
> > +                     break;
> > +             }
> > +             filename_write_helper(trans, fp);
> > +     };
> > +     rhashtable_walk_stop(&iter);
> > +     rhashtable_walk_exit(&iter);
> >       if (rc)
> >               return rc;
> >
> > diff --git a/security/selinux/ss/policydb.h b/security/selinux/ss/policydb.h
> > index bc56b14e2216..f1d2f5166af2 100644
> > --- a/security/selinux/ss/policydb.h
> > +++ b/security/selinux/ss/policydb.h
> > @@ -29,6 +29,7 @@
> >   #include "mls_types.h"
> >   #include "context.h"
> >   #include "constraint.h"
> > +#include <linux/rhashtable.h>
> >
> >   /*
> >    * A datum type is defined for each kind of symbol
> > @@ -90,16 +91,14 @@ struct role_trans {
> >   };
> >
> >   struct filename_trans {
> > +     struct rhash_head hash_head;
> > +     u32 otype;
> >       u32 stype;              /* current process */
> >       u32 ttype;              /* parent dir context */
> >       u16 tclass;             /* class of new object */
> >       const char *name;       /* last path component */
> >   };
> >
> > -struct filename_trans_datum {
> > -     u32 otype;              /* expected of new object */
> > -};
> > -
> >   struct role_allow {
> >       u32 role;               /* current role */
> >       u32 new_role;           /* new role */
> > @@ -266,7 +265,7 @@ struct policydb {
> >       /* quickly exclude lookups when parent ttype has no rules */
> >       struct ebitmap filename_trans_ttypes;
> >       /* actual set of filename_trans rules */
> > -     struct hashtab *filename_trans;
> > +     struct rhashtable filename_trans;
> >
> >       /* bools indexed by (value - 1) */
> >       struct cond_bool_datum **bool_val_to_struct;
> > @@ -318,6 +317,11 @@ extern int policydb_role_isvalid(struct policydb *p, unsigned int role);
> >   extern int policydb_read(struct policydb *p, void *fp);
> >   extern int policydb_write(struct policydb *p, void *fp);
> >
> > +void policydb_filename_compute_type(struct policydb *policydb,
> > +                                 struct context *newcontext,
> > +                                 u32 stype, u32 ttype, u16 tclass,
> > +                                 const char *objname);
> > +
> >   #define PERM_SYMTAB_SIZE 32
> >
> >   #define POLICYDB_CONFIG_MLS    1
> > diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c
> > index a5813c7629c1..60a98d900dd3 100644
> > --- a/security/selinux/ss/services.c
> > +++ b/security/selinux/ss/services.c
> > @@ -1607,32 +1607,6 @@ static int compute_sid_handle_invalid_context(
> >       return -EACCES;
> >   }
> >
> > -static void filename_compute_type(struct policydb *policydb,
> > -                               struct context *newcontext,
> > -                               u32 stype, u32 ttype, u16 tclass,
> > -                               const char *objname)
> > -{
> > -     struct filename_trans ft;
> > -     struct filename_trans_datum *otype;
> > -
> > -     /*
> > -      * Most filename trans rules are going to live in specific directories
> > -      * like /dev or /var/run.  This bitmap will quickly skip rule searches
> > -      * if the ttype does not contain any rules.
> > -      */
> > -     if (!ebitmap_get_bit(&policydb->filename_trans_ttypes, ttype))
> > -             return;
> > -
> > -     ft.stype = stype;
> > -     ft.ttype = ttype;
> > -     ft.tclass = tclass;
> > -     ft.name = objname;
> > -
> > -     otype = hashtab_search(policydb->filename_trans, &ft);
> > -     if (otype)
> > -             newcontext->type = otype->otype;
> > -}
> > -
> >   static int security_compute_sid(struct selinux_state *state,
> >                               u32 ssid,
> >                               u32 tsid,
> > @@ -1770,8 +1744,9 @@ static int security_compute_sid(struct selinux_state *state,
> >
> >       /* if we have a objname this is a file trans check so check those rules */
> >       if (objname)
> > -             filename_compute_type(policydb, &newcontext, scontext->type,
> > -                                   tcontext->type, tclass, objname);
> > +             policydb_filename_compute_type(policydb, &newcontext,
> > +                                            scontext->type, tcontext->type,
> > +                                            tclass, objname);
> >
> >       /* Check for class-specific changes. */
> >       if (specified & AVTAB_TRANSITION) {
> >
>

-- 
Ondrej Mosnacek <omosnace at redhat dot com>
Software Engineer, Security Technologies
Red Hat, Inc.

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