Commit 1748f6a2 authored by Herbert Xu's avatar Herbert Xu Committed by David S. Miller
Browse files

rhashtable: Fix unprotected RCU dereference in __rht_ptr 



The rcu_dereference call in rht_ptr_rcu is completely bogus because
we've already dereferenced the value in __rht_ptr and operated on it.
This causes potential double readings which could be fatal.  The RCU
dereference must occur prior to the comparison in __rht_ptr.

This patch changes the order of RCU dereference so that it is done
first and the result is then fed to __rht_ptr.  The RCU marking
changes have been minimised using casts which will be removed in
a follow-up patch.

Fixes: ba6306e3 ("rhashtable: Remove RCU marking from...")
Reported-by: default avatar"Gong, Sishuai" <sishuai@purdue.edu>
Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 19016d93

include/linux/rhashtable.h

+13 −12
Original line number Diff line number Diff line
@@ -349,11 +349,11 @@ static inline void rht_unlock(struct bucket_table *tbl, 
	local_bh_enable();

}



static inline struct rhash_head __rcu *__rht_ptr(

	struct rhash_lock_head *const *bkt)

static inline struct rhash_head *__rht_ptr(

	struct rhash_lock_head *p, struct rhash_lock_head __rcu *const *bkt)

{

	return (struct rhash_head __rcu *)

		((unsigned long)*bkt & ~BIT(0) ?:

	return (struct rhash_head *)

		((unsigned long)p & ~BIT(0) ?:

		 (unsigned long)RHT_NULLS_MARKER(bkt));

}
@@ -365,25 +365,26 @@ static inline struct rhash_head __rcu *__rht_ptr( 
 *            access is guaranteed, such as when destroying the table.

 */

static inline struct rhash_head *rht_ptr_rcu(

	struct rhash_lock_head *const *bkt)

	struct rhash_lock_head *const *p)

{

	struct rhash_head __rcu *p = __rht_ptr(bkt);



	return rcu_dereference(p);

	struct rhash_lock_head __rcu *const *bkt = (void *)p;

	return __rht_ptr(rcu_dereference(*bkt), bkt);

}



static inline struct rhash_head *rht_ptr(

	struct rhash_lock_head *const *bkt,

	struct rhash_lock_head *const *p,

	struct bucket_table *tbl,

	unsigned int hash)

{

	return rht_dereference_bucket(__rht_ptr(bkt), tbl, hash);

	struct rhash_lock_head __rcu *const *bkt = (void *)p;

	return __rht_ptr(rht_dereference_bucket(*bkt, tbl, hash), bkt);

}



static inline struct rhash_head *rht_ptr_exclusive(

	struct rhash_lock_head *const *bkt)

	struct rhash_lock_head *const *p)

{

	return rcu_dereference_protected(__rht_ptr(bkt), 1);

	struct rhash_lock_head __rcu *const *bkt = (void *)p;

	return __rht_ptr(rcu_dereference_protected(*bkt, 1), bkt);

}



static inline void rht_assign_locked(struct rhash_lock_head **bkt,

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