From: Jeffrey Vander Stoep <jeffv@google.com>
To: Ondrej Mosnacek <omosnace@redhat.com>
Cc: SElinux list <selinux@vger.kernel.org>,
Stephen Smalley <sds@tycho.nsa.gov>,
Jovana Knezevic <jovanak@google.com>
Subject: Re: [PATCH] selinux: sidtab: reverse lookup hash table
Date: Wed, 30 Oct 2019 14:21:04 +0100 [thread overview]
Message-ID: <CABXk95Do9zd5VbR6_aUMisMOWbYdzjkWkhJPQqCqLES3go+EiA@mail.gmail.com> (raw)
In-Reply-To: <CAFqZXNsawo1L2_ToFR5pzn-eLgNAge=kPwA+b1syURQvM_Fhrg@mail.gmail.com>
On Wed, Oct 30, 2019 at 1:38 PM Ondrej Mosnacek <omosnace@redhat.com> wrote:
>
> Hi Jeff,
>
> thank you for working on this! This is certainly a nice improvement.
> See a couple quick comments below.
>
> On Wed, Oct 30, 2019 at 11:20 AM Jeff Vander Stoep <jeffv@google.com> wrote:
> >
> > This replaces the reverse table lookup and reverse cache with a
> > hashtable which improves cache-miss reverese-lookup times from
>
> spelling nit: reverse-lookup
>
> > O(n) to O(1) and maintains the same performance as a reverse
> > cache hit.
>
> This is only half-true, since at some point when the number of
> contexts gets too high, it becomes O(n) again
> (SIDTAB_HASH_BUCKETS-times faster O(n), but still O(n) :). To make it
> really O(1) you'd need to dynamically resize the hashtable (which I
> recently tried to implement, but then got stuck - it is really hard to
> do it without too much locking...). But of course this is just a
> formal nitpick, a fixed-size hashtable is still much better than no
> hashtable :)
>
> >
> > This reduces the time needed to add a new sidtab entry from ~500us
> > to 5us on a Pixel 3 when there are ~10,000 sidtab entries.
> >
> > The implementation uses the kernel's generic hashtable API,
> > It uses the context's string represtation as the hash source,
>
> spelling nit: representation
>
> > and the kernels generic string hashing algorithm full_name_hash()
> > to reduce the string to a 32 bit value.
>
> If I'm not mistaken, the context strings have a caveat that after a
> policy reload the canonical string representation of a given context
> (SID) can change slightly (IIRC it has to do with ordering of the
> levels/categories). I didn't dive deep enough into the patch to be
> sure if this may cause issues here, but it is definitely something to
> watch out for. Stephen and Paul know the guts of SELinux better than
> me, so hopefully they'll be able to provide more insight here.
>
I believe this is already handled. A new hash is calculated using the new
string representation in context_convert().
> >
> > This change also maintains the improvement introduced in commit
> > ee1a84fd which removed the need to keep the current sidtab locked
> > during policy reload. It does however introduce periodic locking of
> > the target sidtab while converting the hashtable. Sidtab entries
> > are never modified or removed, so the context struct stored in the
> > sid_to_context tree can also be used for the context_to_sid
> > hashtable to reduce memory usage.
> >
> > This bug was reported by:
> > - Stephen Smally on the selinux bug tracker.
> > BUG: kernel softlockup due to too many SIDs/contexts #37
> > https://github.com/SELinuxProject/selinux-kernel/issues/37
> > - Jovana Knezevic on Android's bugtracker.
> > Bug: 140252993
> > "During multi-user performance testing, we create and remove users
> > many times. selinux_android_restorecon_pkgdir goes from 1ms to over
> > 20ms after about 200 user creations and removals. Accumulated over
> > ~280 packages, that adds a significant time to user creation,
> > making perf benchmarks unreliable."
> >
> > Signed-off-by: Jeff Vander Stoep <jeffv@google.com>
> > Reported-by: Stephen Smalley <sds@tycho.nsa.gov>
> > Reported-by: Jovana Knezevic <jovanak@google.com>
> > ---
> > security/selinux/include/security.h | 1 +
> > security/selinux/selinuxfs.c | 27 +++
> > security/selinux/ss/context.h | 9 +
> > security/selinux/ss/policydb.c | 5 +
> > security/selinux/ss/services.c | 81 +++++---
> > security/selinux/ss/services.h | 4 +-
> > security/selinux/ss/sidtab.c | 283 ++++++++++++++++------------
> > security/selinux/ss/sidtab.h | 20 +-
> > 8 files changed, 283 insertions(+), 147 deletions(-)
> >
> > diff --git a/security/selinux/include/security.h b/security/selinux/include/security.h
> > index ae840634e3c7..8c0dbbd076c6 100644
> > --- a/security/selinux/include/security.h
> > +++ b/security/selinux/include/security.h
> > @@ -395,5 +395,6 @@ extern int selinux_nlmsg_lookup(u16 sclass, u16 nlmsg_type, u32 *perm);
> > extern void avtab_cache_init(void);
> > extern void ebitmap_cache_init(void);
> > extern void hashtab_cache_init(void);
> > +extern int security_sidtab_hash_stats(struct selinux_state *state, char *page);
> >
> > #endif /* _SELINUX_SECURITY_H_ */
> > diff --git a/security/selinux/selinuxfs.c b/security/selinux/selinuxfs.c
> > index ee94fa469c29..ebdec88d9ccb 100644
> > --- a/security/selinux/selinuxfs.c
> > +++ b/security/selinux/selinuxfs.c
> > @@ -1482,6 +1482,32 @@ static ssize_t sel_read_avc_hash_stats(struct file *filp, char __user *buf,
> > return length;
> > }
> >
> > +static ssize_t sel_read_sidtab_hash_stats(struct file *filp, char __user *buf,
> > + size_t count, loff_t *ppos)
> > +{
> > + struct selinux_fs_info *fsi = file_inode(filp)->i_sb->s_fs_info;
> > + struct selinux_state *state = fsi->state;
> > + char *page;
> > + ssize_t length;
> > +
> > + page = (char *)__get_free_page(GFP_KERNEL);
> > + if (!page)
> > + return -ENOMEM;
> > +
> > + length = security_sidtab_hash_stats(state, page);
> > + if (length >= 0)
> > + length = simple_read_from_buffer(buf, count, ppos, page,
> > + length);
> > + free_page((unsigned long)page);
> > +
> > + return length;
> > +}
> > +
> > +static const struct file_operations sel_sidtab_hash_stats_ops = {
> > + .read = sel_read_sidtab_hash_stats,
> > + .llseek = generic_file_llseek,
> > +};
> > +
> > static const struct file_operations sel_avc_cache_threshold_ops = {
> > .read = sel_read_avc_cache_threshold,
> > .write = sel_write_avc_cache_threshold,
> > @@ -1572,6 +1598,7 @@ static int sel_make_avc_files(struct dentry *dir)
> > { "cache_threshold",
> > &sel_avc_cache_threshold_ops, S_IRUGO|S_IWUSR },
> > { "hash_stats", &sel_avc_hash_stats_ops, S_IRUGO },
> > + { "sidtab_hash_stats", &sel_sidtab_hash_stats_ops, S_IRUGO },
> > #ifdef CONFIG_SECURITY_SELINUX_AVC_STATS
> > { "cache_stats", &sel_avc_cache_stats_ops, S_IRUGO },
> > #endif
> > diff --git a/security/selinux/ss/context.h b/security/selinux/ss/context.h
> > index 513e67f48878..01fea944177d 100644
> > --- a/security/selinux/ss/context.h
> > +++ b/security/selinux/ss/context.h
> > @@ -31,6 +31,7 @@ struct context {
> > u32 len; /* length of string in bytes */
> > struct mls_range range;
> > char *str; /* string representation if context cannot be mapped. */
> > + u32 hash; /* a hash of the string representation */
> > };
> >
> > static inline void mls_context_init(struct context *c)
> > @@ -168,6 +169,7 @@ static inline int context_cpy(struct context *dst, struct context *src)
> > kfree(dst->str);
> > return rc;
> > }
> > + dst->hash = src->hash;
> > return 0;
> > }
> >
> > @@ -182,6 +184,8 @@ static inline void context_destroy(struct context *c)
> >
> > static inline int context_cmp(struct context *c1, struct context *c2)
> > {
> > + if (c1->hash && c2->hash && (c1->hash != c2->hash))
> > + return 0;
> > if (c1->len && c2->len)
> > return (c1->len == c2->len && !strcmp(c1->str, c2->str));
> > if (c1->len || c2->len)
> > @@ -192,5 +196,10 @@ static inline int context_cmp(struct context *c1, struct context *c2)
> > mls_context_cmp(c1, c2));
> > }
> >
> > +static inline unsigned int context_compute_hash(const char *s)
> > +{
> > + return full_name_hash(NULL, s, strlen(s));
> > +}
> > +
> > #endif /* _SS_CONTEXT_H_ */
> >
> > diff --git a/security/selinux/ss/policydb.c b/security/selinux/ss/policydb.c
> > index e20624a68f5d..e369b0092cdf 100644
> > --- a/security/selinux/ss/policydb.c
> > +++ b/security/selinux/ss/policydb.c
> > @@ -878,6 +878,11 @@ int policydb_load_isids(struct policydb *p, struct sidtab *s)
> > sidtab_destroy(s);
> > goto out;
> > }
> > + rc = context_add_hash(p, &c->context[0]);
> > + if (rc) {
> > + sidtab_destroy(s);
> > + goto out;
> > + }
> >
> > rc = sidtab_set_initial(s, c->sid[0], &c->context[0]);
> > if (rc) {
> > diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c
> > index a5813c7629c1..29076c15cdf7 100644
> > --- a/security/selinux/ss/services.c
> > +++ b/security/selinux/ss/services.c
> > @@ -1257,6 +1257,11 @@ static int context_struct_to_string(struct policydb *p,
> >
> > #include "initial_sid_to_string.h"
> >
> > +int security_sidtab_hash_stats(struct selinux_state *state, char *page)
> > +{
> > + return sidtab_hash_stats(state->ss->sidtab, page);
> > +}
> > +
> > const char *security_get_initial_sid_context(u32 sid)
> > {
> > if (unlikely(sid > SECINITSID_NUM))
> > @@ -1384,6 +1389,8 @@ static int string_to_context_struct(struct policydb *pol,
> > int rc = 0;
> >
> > context_init(ctx);
> > + /* hash the string before it gets mutated */
> > + ctx->hash = context_compute_hash(scontext);
> >
> > /* Parse the security context. */
> >
> > @@ -1442,6 +1449,7 @@ static int string_to_context_struct(struct policydb *pol,
> > rc = -EINVAL;
> > if (!policydb_context_isvalid(pol, ctx))
> > goto out;
> > +
> > rc = 0;
> > out:
> > if (rc)
> > @@ -1449,6 +1457,42 @@ static int string_to_context_struct(struct policydb *pol,
> > return rc;
> > }
> >
> > +int context_add_hash(struct policydb *policydb,
> > + struct context *context)
> > +{
> > + int rc;
> > + char *str;
> > + int len;
> > +
> > + if (context->str) {
> > + context->hash = context_compute_hash(context->str);
> > + } else {
> > + rc = context_struct_to_string(policydb, context,
> > + &str, &len);
> > + if (rc)
> > + return rc;
> > + context->hash = context_compute_hash(str);
> > + kfree(str);
> > + }
> > + return 0;
> > +}
> > +
> > +static int context_to_sid(struct selinux_state *state,
> > + struct context *context, u32 *sid)
> > +{
> > + int rc;
> > + struct sidtab *sidtab = state->ss->sidtab;
> > + struct policydb *policydb = &state->ss->policydb;
> > +
> > + if (!context->hash) {
> > + rc = context_add_hash(policydb, context);
> > + if (rc)
> > + return rc;
> > + }
> > +
> > + return sidtab_context_to_sid(sidtab, context, sid);
> > +}
> > +
> > static int security_context_to_sid_core(struct selinux_state *state,
> > const char *scontext, u32 scontext_len,
> > u32 *sid, u32 def_sid, gfp_t gfp_flags,
> > @@ -1501,7 +1545,7 @@ static int security_context_to_sid_core(struct selinux_state *state,
> > str = NULL;
> > } else if (rc)
> > goto out_unlock;
> > - rc = sidtab_context_to_sid(sidtab, &context, sid);
> > + rc = context_to_sid(state, &context, sid);
> > context_destroy(&context);
> > out_unlock:
> > read_unlock(&state->ss->policy_rwlock);
> > @@ -1805,7 +1849,7 @@ static int security_compute_sid(struct selinux_state *state,
> > goto out_unlock;
> > }
> > /* Obtain the sid for the context. */
> > - rc = sidtab_context_to_sid(sidtab, &newcontext, out_sid);
> > + rc = context_to_sid(state, &newcontext, out_sid);
> > out_unlock:
> > read_unlock(&state->ss->policy_rwlock);
> > context_destroy(&newcontext);
> > @@ -2033,6 +2077,10 @@ static int convert_context(struct context *oldc, struct context *newc, void *p)
> > goto bad;
> > }
> >
> > + rc = context_add_hash(args->newp, newc);
> > + if (rc)
> > + goto bad;
> > +
> > return 0;
> > bad:
> > /* Map old representation to string and save it. */
> > @@ -2280,9 +2328,7 @@ int security_port_sid(struct selinux_state *state,
> >
> > if (c) {
> > if (!c->sid[0]) {
> > - rc = sidtab_context_to_sid(sidtab,
> > - &c->context[0],
> > - &c->sid[0]);
> > + rc = context_to_sid(state, &c->context[0], &c->sid[0]);
> > if (rc)
> > goto out;
> > }
> > @@ -2374,9 +2420,7 @@ int security_ib_endport_sid(struct selinux_state *state,
> >
> > if (c) {
> > if (!c->sid[0]) {
> > - rc = sidtab_context_to_sid(sidtab,
> > - &c->context[0],
> > - &c->sid[0]);
> > + rc = context_to_sid(state, &c->context[0], &c->sid[0]);
> > if (rc)
> > goto out;
> > }
> > @@ -2416,14 +2460,10 @@ int security_netif_sid(struct selinux_state *state,
> >
> > if (c) {
> > if (!c->sid[0] || !c->sid[1]) {
> > - rc = sidtab_context_to_sid(sidtab,
> > - &c->context[0],
> > - &c->sid[0]);
> > + rc = context_to_sid(state, &c->context[0], &c->sid[0]);
> > if (rc)
> > goto out;
> > - rc = sidtab_context_to_sid(sidtab,
> > - &c->context[1],
> > - &c->sid[1]);
> > + rc = context_to_sid(state, &c->context[1], &c->sid[1]);
> > if (rc)
> > goto out;
> > }
> > @@ -2601,7 +2641,7 @@ int security_get_user_sids(struct selinux_state *state,
> > &usercon))
> > continue;
> >
> > - rc = sidtab_context_to_sid(sidtab, &usercon, &sid);
> > + rc = context_to_sid(state, &usercon, &sid);
> > if (rc)
> > goto out_unlock;
> > if (mynel < maxnel) {
> > @@ -2672,7 +2712,6 @@ static inline int __security_genfs_sid(struct selinux_state *state,
> > u32 *sid)
> > {
> > struct policydb *policydb = &state->ss->policydb;
> > - struct sidtab *sidtab = state->ss->sidtab;
> > int len;
> > u16 sclass;
> > struct genfs *genfs;
> > @@ -2707,7 +2746,7 @@ static inline int __security_genfs_sid(struct selinux_state *state,
> > goto out;
> >
> > if (!c->sid[0]) {
> > - rc = sidtab_context_to_sid(sidtab, &c->context[0], &c->sid[0]);
> > + rc = context_to_sid(state, &c->context[0], &c->sid[0]);
> > if (rc)
> > goto out;
> > }
> > @@ -2770,8 +2809,7 @@ int security_fs_use(struct selinux_state *state, struct super_block *sb)
> > if (c) {
> > sbsec->behavior = c->v.behavior;
> > if (!c->sid[0]) {
> > - rc = sidtab_context_to_sid(sidtab, &c->context[0],
> > - &c->sid[0]);
> > + rc = context_to_sid(state, &c->context[0], &c->sid[0]);
> > if (rc)
> > goto out;
> > }
> > @@ -3026,8 +3064,7 @@ int security_sid_mls_copy(struct selinux_state *state,
> > goto out_unlock;
> > }
> > }
> > -
> > - rc = sidtab_context_to_sid(sidtab, &newcon, new_sid);
> > + rc = context_to_sid(state, &newcon, new_sid);
> > out_unlock:
> > read_unlock(&state->ss->policy_rwlock);
> > context_destroy(&newcon);
> > @@ -3620,7 +3657,7 @@ int security_netlbl_secattr_to_sid(struct selinux_state *state,
> > if (!mls_context_isvalid(policydb, &ctx_new))
> > goto out_free;
> >
> > - rc = sidtab_context_to_sid(sidtab, &ctx_new, sid);
> > + rc = context_to_sid(state, &ctx_new, sid);
> > if (rc)
> > goto out_free;
> >
> > diff --git a/security/selinux/ss/services.h b/security/selinux/ss/services.h
> > index 9a36de860368..fc40640a9725 100644
> > --- a/security/selinux/ss/services.h
> > +++ b/security/selinux/ss/services.h
> > @@ -8,7 +8,7 @@
> > #define _SS_SERVICES_H_
> >
> > #include "policydb.h"
> > -#include "sidtab.h"
> > +#include "context.h"
> >
> > /* Mapping for a single class */
> > struct selinux_mapping {
> > @@ -39,4 +39,6 @@ void services_compute_xperms_drivers(struct extended_perms *xperms,
> > void services_compute_xperms_decision(struct extended_perms_decision *xpermd,
> > struct avtab_node *node);
> >
> > +int context_add_hash(struct policydb *policydb, struct context *context);
> > +
> > #endif /* _SS_SERVICES_H_ */
> > diff --git a/security/selinux/ss/sidtab.c b/security/selinux/ss/sidtab.c
> > index 7d49994e8d5f..e4710f32b6d9 100644
> > --- a/security/selinux/ss/sidtab.c
> > +++ b/security/selinux/ss/sidtab.c
> > @@ -23,23 +23,32 @@ int sidtab_init(struct sidtab *s)
> >
> > memset(s->roots, 0, sizeof(s->roots));
> >
> > - /* max count is SIDTAB_MAX so valid index is always < SIDTAB_MAX */
> > - for (i = 0; i < SIDTAB_RCACHE_SIZE; i++)
> > - s->rcache[i] = SIDTAB_MAX;
> > -
> > for (i = 0; i < SECINITSID_NUM; i++)
> > s->isids[i].set = 0;
> >
> > s->count = 0;
> > s->convert = NULL;
> > + hash_init(s->context_to_sid);
> >
> > spin_lock_init(&s->lock);
> > return 0;
> > }
> >
> > +static u32 context_to_sid(struct sidtab *s, struct context *context)
> > +{
> > + struct sidtab_node *node;
> > +
> > + hash_for_each_possible(s->context_to_sid, node, list, context->hash) {
> > + if (context_cmp(node->context, context))
> > + return node->sid;
> > + }
> > + return 0;
> > +}
> > +
> > int sidtab_set_initial(struct sidtab *s, u32 sid, struct context *context)
> > {
> > struct sidtab_isid_entry *entry;
> > + struct sidtab_node *node = NULL;
> > int rc;
> >
> > if (sid == 0 || sid > SECINITSID_NUM)
> > @@ -52,9 +61,57 @@ int sidtab_set_initial(struct sidtab *s, u32 sid, struct context *context)
> > return rc;
> >
> > entry->set = 1;
> > +
> > + /*
> > + * Multiple initial sids may map to the same context. Check that this
> > + * context is not already represented in the context_to_sid hashtable
> > + * to avoid duplicate entries and long linked lists upon hash
> > + * collision.
> > + */
> > + if (!context_to_sid(s, context)) {
> > + node = kzalloc(sizeof(struct sidtab_node), GFP_ATOMIC);
> > + if (!node)
> > + return -ENOMEM;
> > + node->sid = sid;
> > + node->context = &entry->context;
> > + hash_add(s->context_to_sid, &node->list, context->hash);
> > + }
> > +
> > return 0;
> > }
> >
> > +int sidtab_hash_stats(struct sidtab *sidtab, char *page)
> > +{
> > + int i;
> > + int chain_len = 0;
> > + int slots_used = 0;
> > + int entries = 0;
> > + int max_chain_len = 0;
> > + int cur_bucket = 0;
> > + struct sidtab_node *node;
> > +
> > +
> > + hash_for_each(sidtab->context_to_sid, i, node, list) {
> > + entries++;
> > + if (i == cur_bucket) {
> > + chain_len++;
> > + if (chain_len == 1)
> > + slots_used++;
> > + } else {
> > + cur_bucket = i;
> > + if (chain_len > max_chain_len)
> > + max_chain_len = chain_len;
> > + chain_len = 0;
> > + }
> > + }
> > + if (chain_len > max_chain_len)
> > + max_chain_len = chain_len;
> > + return scnprintf(page, PAGE_SIZE, "%s: %d entries and %d/%d buckets "
> > + "used, longest chain length %d\n", "context_to_sid",
> > + entries, slots_used, SIDTAB_HASH_BUCKETS,
> > + max_chain_len);
> > +}
> > +
> > static u32 sidtab_level_from_count(u32 count)
> > {
> > u32 capacity = SIDTAB_LEAF_ENTRIES;
> > @@ -150,7 +207,7 @@ static struct context *sidtab_search_core(struct sidtab *s, u32 sid, int force)
> >
> > if (sid != 0) {
> > if (sid > SECINITSID_NUM)
> > - context = sidtab_lookup(s, sid - (SECINITSID_NUM + 1));
> > + context = sidtab_lookup(s, sid_to_index(sid));
> > else
> > context = sidtab_lookup_initial(s, sid);
> > if (context && (!context->len || force))
> > @@ -170,132 +227,70 @@ struct context *sidtab_search_force(struct sidtab *s, u32 sid)
> > return sidtab_search_core(s, sid, 1);
> > }
> >
> > -static int sidtab_find_context(union sidtab_entry_inner entry,
> > - u32 *pos, u32 count, u32 level,
> > - struct context *context, u32 *index)
> > -{
> > - int rc;
> > - u32 i;
> > -
> > - if (level != 0) {
> > - struct sidtab_node_inner *node = entry.ptr_inner;
> > -
> > - i = 0;
> > - while (i < SIDTAB_INNER_ENTRIES && *pos < count) {
> > - rc = sidtab_find_context(node->entries[i],
> > - pos, count, level - 1,
> > - context, index);
> > - if (rc == 0)
> > - return 0;
> > - i++;
> > - }
> > - } else {
> > - struct sidtab_node_leaf *node = entry.ptr_leaf;
> > -
> > - i = 0;
> > - while (i < SIDTAB_LEAF_ENTRIES && *pos < count) {
> > - if (context_cmp(&node->entries[i].context, context)) {
> > - *index = *pos;
> > - return 0;
> > - }
> > - (*pos)++;
> > - i++;
> > - }
> > - }
> > - return -ENOENT;
> > -}
> > -
> > -static void sidtab_rcache_update(struct sidtab *s, u32 index, u32 pos)
> > -{
> > - while (pos > 0) {
> > - WRITE_ONCE(s->rcache[pos], READ_ONCE(s->rcache[pos - 1]));
> > - --pos;
> > - }
> > - WRITE_ONCE(s->rcache[0], index);
> > -}
> > -
> > -static void sidtab_rcache_push(struct sidtab *s, u32 index)
> > -{
> > - sidtab_rcache_update(s, index, SIDTAB_RCACHE_SIZE - 1);
> > -}
> > -
> > -static int sidtab_rcache_search(struct sidtab *s, struct context *context,
> > - u32 *index)
> > -{
> > - u32 i;
> > -
> > - for (i = 0; i < SIDTAB_RCACHE_SIZE; i++) {
> > - u32 v = READ_ONCE(s->rcache[i]);
> > -
> > - if (v >= SIDTAB_MAX)
> > - continue;
> > -
> > - if (context_cmp(sidtab_do_lookup(s, v, 0), context)) {
> > - sidtab_rcache_update(s, v, i);
> > - *index = v;
> > - return 0;
> > - }
> > - }
> > - return -ENOENT;
> > -}
> > -
> > -static int sidtab_reverse_lookup(struct sidtab *s, struct context *context,
> > - u32 *index)
> > +int sidtab_context_to_sid(struct sidtab *s, struct context *context,
> > + u32 *sid)
> > {
> > unsigned long flags;
> > - u32 count, count_locked, level, pos;
> > + u32 count;
> > struct sidtab_convert_params *convert;
> > struct context *dst, *dst_convert;
> > + struct sidtab_node *dst_node, *dst_node_convert = NULL;
> > int rc;
> >
> > - rc = sidtab_rcache_search(s, context, index);
> > - if (rc == 0)
> > - return 0;
> > -
> > - /* read entries only after reading count */
> > - count = smp_load_acquire(&s->count);
> > - level = sidtab_level_from_count(count);
> > -
> > - pos = 0;
> > - rc = sidtab_find_context(s->roots[level], &pos, count, level,
> > - context, index);
> > - if (rc == 0) {
> > - sidtab_rcache_push(s, *index);
> > + *sid = context_to_sid(s, context);
> > + if (*sid)
> > return 0;
> > - }
> >
> > /* lock-free search failed: lock, re-search, and insert if not found */
> > spin_lock_irqsave(&s->lock, flags);
> >
> > + *sid = context_to_sid(s, context);
> > + if (*sid)
> > + goto out_unlock;
> > +
> > convert = s->convert;
> > - count_locked = s->count;
> > - level = sidtab_level_from_count(count_locked);
> > -
> > - /* if count has changed before we acquired the lock, then catch up */
> > - while (count < count_locked) {
> > - if (context_cmp(sidtab_do_lookup(s, count, 0), context)) {
> > - sidtab_rcache_push(s, count);
> > - *index = count;
> > - rc = 0;
> > + count = s->count;
> > +
> > + rc = -ENOMEM;
> > + dst_node = kzalloc(sizeof(struct sidtab_node), GFP_ATOMIC);
> > + if (!dst_node)
> > + goto out_unlock;
> > +
> > + if (convert) {
> > + dst_node_convert = kzalloc(sizeof(struct sidtab_node),
> > + GFP_ATOMIC);
> > + if (!dst_node_convert) {
> > + kfree(dst_node);
> > goto out_unlock;
> > }
> > - ++count;
> > }
> >
> > /* bail out if we already reached max entries */
> > rc = -EOVERFLOW;
> > - if (count >= SIDTAB_MAX)
> > + if (count >= SIDTAB_MAX) {
> > + kfree(dst_node);
> > + kfree(dst_node_convert);
> > goto out_unlock;
> > + }
> >
> > /* insert context into new entry */
> > rc = -ENOMEM;
> > dst = sidtab_do_lookup(s, count, 1);
> > - if (!dst)
> > + if (!dst) {
> > + kfree(dst_node);
> > + kfree(dst_node_convert);
> > goto out_unlock;
> > + }
> > +
> > + dst_node->sid = index_to_sid(count);
> > + dst_node->context = dst;
> >
> > rc = context_cpy(dst, context);
> > - if (rc)
> > + if (rc) {
> > + kfree(dst_node);
> > + kfree(dst_node_convert);
> > goto out_unlock;
> > + }
> >
> > /*
> > * if we are building a new sidtab, we need to convert the context
> > @@ -306,25 +301,35 @@ static int sidtab_reverse_lookup(struct sidtab *s, struct context *context,
> > dst_convert = sidtab_do_lookup(convert->target, count, 1);
> > if (!dst_convert) {
> > context_destroy(dst);
> > + kfree(dst_node);
> > + kfree(dst_node_convert);
> > goto out_unlock;
> > }
> >
> > rc = convert->func(context, dst_convert, convert->args);
> > if (rc) {
> > context_destroy(dst);
> > + kfree(dst_node);
> > + kfree(dst_node_convert);
> > goto out_unlock;
> > }
> > + dst_node_convert->sid = index_to_sid(count);
> > + dst_node_convert->context = dst_convert;
> >
> > /* at this point we know the insert won't fail */
> > + spin_lock_irqsave(&convert->target->lock, flags);
> > convert->target->count = count + 1;
> > + hash_add(convert->target->context_to_sid,
> > + &dst_node_convert->list, dst_convert->hash);
> > + spin_unlock_irqrestore(&convert->target->lock, flags);
> > }
> > + hash_add(s->context_to_sid, &dst_node->list, context->hash);
> >
> > if (context->len)
> > pr_info("SELinux: Context %s is not valid (left unmapped).\n",
> > context->str);
> >
> > - sidtab_rcache_push(s, count);
> > - *index = count;
> > + *sid = index_to_sid(count);
> >
> > /* write entries before writing new count */
> > smp_store_release(&s->count, count + 1);
> > @@ -335,27 +340,41 @@ static int sidtab_reverse_lookup(struct sidtab *s, struct context *context,
> > return rc;
> > }
> >
> > -int sidtab_context_to_sid(struct sidtab *s, struct context *context, u32 *sid)
> > +static int sidtab_convert_hashnode(struct sidtab *s, u32 index)
> > {
> > - int rc;
> > - u32 i;
> > + unsigned long flags;
> > + struct context *context;
> > + struct sidtab_node *node;
> >
> > - for (i = 0; i < SECINITSID_NUM; i++) {
> > - struct sidtab_isid_entry *entry = &s->isids[i];
> > + context = sidtab_do_lookup(s, index, 0);
> >
> > - if (entry->set && context_cmp(context, &entry->context)) {
> > - *sid = i + 1;
> > - return 0;
> > - }
> > - }
> > + node = kzalloc(sizeof(struct sidtab_node), GFP_ATOMIC);
> > + if (!node)
> > + return -ENOMEM;
> >
> > - rc = sidtab_reverse_lookup(s, context, sid);
> > - if (rc)
> > - return rc;
> > - *sid += SECINITSID_NUM + 1;
> > + node->sid = index_to_sid(index);
> > + node->context = context;
> > + spin_lock_irqsave(&s->lock, flags);
> > + hash_add(s->context_to_sid, &node->list, context->hash);
> > + spin_unlock_irqrestore(&s->lock, flags);
> > return 0;
> > }
> >
> > +static int sidtab_convert_hashtable(struct sidtab *s, u32 count)
> > +{
> > + u32 i;
> > + int rc = 0;
> > +
> > + for (i = 0; i < count; i++) {
> > + rc = sidtab_convert_hashnode(s, i);
> > + if (rc)
> > + break;
> > +
> > + cond_resched();
> > + }
> > + return rc;
> > +}
> > +
> > static int sidtab_convert_tree(union sidtab_entry_inner *edst,
> > union sidtab_entry_inner *esrc,
> > u32 *pos, u32 count, u32 level,
> > @@ -400,6 +419,7 @@ static int sidtab_convert_tree(union sidtab_entry_inner *edst,
> > }
> > cond_resched();
> > }
> > +
> > return 0;
> > }
> >
> > @@ -449,7 +469,16 @@ int sidtab_convert(struct sidtab *s, struct sidtab_convert_params *params)
> > spin_lock_irqsave(&s->lock, flags);
> > s->convert = NULL;
> > spin_unlock_irqrestore(&s->lock, flags);
> > + return rc;
> > + }
> > +
> > + rc = sidtab_convert_hashtable(params->target, count);
> > + if (rc) {
> > + spin_lock_irqsave(&s->lock, flags);
> > + s->convert = NULL;
> > + spin_unlock_irqrestore(&s->lock, flags);
> > }
> > +
> > return rc;
> > }
> >
> > @@ -478,6 +507,19 @@ static void sidtab_destroy_tree(union sidtab_entry_inner entry, u32 level)
> > }
> > }
> >
> > +
>
> Extraneous newline?
>
> > +static void sidtab_destroy_hashtable(struct sidtab *s)
> > +{
> > + struct sidtab_node *node;
> > + struct hlist_node *tmp;
> > + int i;
> > +
> > + hash_for_each_safe(s->context_to_sid, i, tmp, node, list) {
> > + hash_del(&node->list);
> > + kfree(node);
> > + }
> > +}
> > +
> > void sidtab_destroy(struct sidtab *s)
> > {
> > u32 i, level;
> > @@ -491,4 +533,5 @@ void sidtab_destroy(struct sidtab *s)
> > --level;
> >
> > sidtab_destroy_tree(s->roots[level], level);
> > + sidtab_destroy_hashtable(s);
> > }
> > diff --git a/security/selinux/ss/sidtab.h b/security/selinux/ss/sidtab.h
> > index 1f4763141aa1..85afef719a43 100644
> > --- a/security/selinux/ss/sidtab.h
> > +++ b/security/selinux/ss/sidtab.h
> > @@ -13,6 +13,7 @@
> >
> > #include <linux/spinlock_types.h>
> > #include <linux/log2.h>
> > +#include <linux/hashtable.h>
> >
> > #include "context.h"
> >
> > @@ -66,7 +67,16 @@ struct sidtab_convert_params {
> > struct sidtab *target;
> > };
> >
> > -#define SIDTAB_RCACHE_SIZE 3
> > +struct sidtab_node {
> > + u32 sid;
> > + struct context *context;
> > + struct hlist_node list;
> > +};
>
> How about just adding the sid and hlist_node fields directly to struct
> sidtab_entry_leaf and add that to the hash table? That should simplify
> the code a lot and also reduce memory allocation overhead.
Oh, good idea. That will definitely simplify things.
>
> > +
> > +#define SIDTAB_HASH_BITS 9
> > +#define SIDTAB_HASH_BUCKETS (1 << SIDTAB_HASH_BITS)
>
> Maybe we should make SIDTAB_HASH_BITS configurable via Kconfig?
>
> > +#define index_to_sid(index) (index + SECINITSID_NUM + 1)
> > +#define sid_to_index(sid) (sid - (SECINITSID_NUM + 1))
>
> I think these last two macros should be rather defined inside
> sidtab.c, since they are not useful outside sidtab internals.
>
> >
> > struct sidtab {
> > /*
> > @@ -83,11 +93,11 @@ struct sidtab {
> > struct sidtab_convert_params *convert;
> > spinlock_t lock;
> >
> > - /* reverse lookup cache - access atomically via {READ|WRITE}_ONCE() */
> > - u32 rcache[SIDTAB_RCACHE_SIZE];
> > -
> > /* index == SID - 1 (no entry for SECSID_NULL) */
> > struct sidtab_isid_entry isids[SECINITSID_NUM];
> > +
> > + /* Hash table for fast reverse context-to-sid lookups. */
> > + DECLARE_HASHTABLE(context_to_sid, SIDTAB_HASH_BITS);
> > };
> >
> > int sidtab_init(struct sidtab *s);
> > @@ -101,6 +111,8 @@ int sidtab_context_to_sid(struct sidtab *s, struct context *context, u32 *sid);
> >
> > void sidtab_destroy(struct sidtab *s);
> >
> > +int sidtab_hash_stats(struct sidtab *sidtab, char *page);
> > +
> > #endif /* _SS_SIDTAB_H_ */
> >
> >
> > --
> > 2.24.0.rc0.303.g954a862665-goog
> >
>
> --
> Ondrej Mosnacek <omosnace at redhat dot com>
> Software Engineer, Security Technologies
> Red Hat, Inc.
>
next prev parent reply other threads:[~2019-10-30 13:21 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-30 10:19 [PATCH] selinux: sidtab: reverse lookup hash table Jeff Vander Stoep
2019-10-30 12:37 ` Ondrej Mosnacek
2019-10-30 13:21 ` Jeffrey Vander Stoep [this message]
2019-10-30 15:24 ` Stephen Smalley
2019-10-30 16:32 ` Stephen Smalley
2019-10-30 16:36 ` Stephen Smalley
2019-10-30 17:14 ` Stephen Smalley
2019-10-30 18:06 ` Stephen Smalley
2019-10-30 18:33 ` Jeffrey Vander Stoep
2019-10-30 18:57 ` Stephen Smalley
2019-10-30 19:07 ` Jeffrey Vander Stoep
2019-10-30 20:02 ` Stephen Smalley
2019-10-30 20:06 ` Jeffrey Vander Stoep
2019-10-30 20:48 ` Paul Moore
2019-11-02 19:52 ` Ondrej Mosnacek
2019-11-07 20:52 Jeff Vander Stoep
2019-11-15 0:04 ` Paul Moore
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