| Message ID | 20200625215548.389774-3-keescook@chromium.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | mm: Expand CONFIG_SLAB_FREELIST_HARDENED to include SLAB | expand |
On 6/25/20 11:55 PM, Kees Cook wrote: > Similar to commit ce6fa91b9363 ("mm/slub.c: add a naive detection > of double free or corruption"), add a very cheap double-free check > for SLAB under CONFIG_SLAB_FREELIST_HARDENED. With this added, the > "SLAB_FREE_DOUBLE" LKDTM test passes under SLAB: > > lkdtm: Performing direct entry SLAB_FREE_DOUBLE > lkdtm: Attempting double slab free ... > ------------[ cut here ]------------ > WARNING: CPU: 2 PID: 2193 at mm/slab.c:757 ___cache _free+0x325/0x390 > > Signed-off-by: Kees Cook <keescook@chromium.org> No idea how much it helps in practice wrt security, but implementation-wise it seems fine, so: Acked-by: Vlastimil Babka <vbabka@suse.cz> Maybe you don't want to warn just once, though? We had similar discussion on cache_to_obj(). > --- > mm/slab.c | 14 ++++++++++++-- > 1 file changed, 12 insertions(+), 2 deletions(-) > > diff --git a/mm/slab.c b/mm/slab.c > index ebac5e400ad0..bbff6705ab2b 100644 > --- a/mm/slab.c > +++ b/mm/slab.c > @@ -749,6 +749,16 @@ static void drain_alien_cache(struct kmem_cache *cachep, > } > } > > +/* &alien->lock must be held by alien callers. */ > +static __always_inline void __free_one(struct array_cache *ac, void *objp) > +{ > + /* Avoid trivial double-free. */ > + if (IS_ENABLED(CONFIG_SLAB_FREELIST_HARDENED) && > + WARN_ON_ONCE(ac->avail > 0 && ac->entry[ac->avail - 1] == objp)) > + return; > + ac->entry[ac->avail++] = objp; > +} > + > static int __cache_free_alien(struct kmem_cache *cachep, void *objp, > int node, int page_node) > { > @@ -767,7 +777,7 @@ static int __cache_free_alien(struct kmem_cache *cachep, void *objp, > STATS_INC_ACOVERFLOW(cachep); > __drain_alien_cache(cachep, ac, page_node, &list); > } > - ac->entry[ac->avail++] = objp; > + __free_one(ac, objp); > spin_unlock(&alien->lock); > slabs_destroy(cachep, &list); > } else { > @@ -3457,7 +3467,7 @@ void ___cache_free(struct kmem_cache *cachep, void *objp, > } > } > > - ac->entry[ac->avail++] = objp; > + __free_one(ac, objp); > } > > /** >
diff --git a/mm/slab.c b/mm/slab.c index ebac5e400ad0..bbff6705ab2b 100644 --- a/mm/slab.c +++ b/mm/slab.c @@ -749,6 +749,16 @@ static void drain_alien_cache(struct kmem_cache *cachep, } } +/* &alien->lock must be held by alien callers. */ +static __always_inline void __free_one(struct array_cache *ac, void *objp) +{ + /* Avoid trivial double-free. */ + if (IS_ENABLED(CONFIG_SLAB_FREELIST_HARDENED) && + WARN_ON_ONCE(ac->avail > 0 && ac->entry[ac->avail - 1] == objp)) + return; + ac->entry[ac->avail++] = objp; +} + static int __cache_free_alien(struct kmem_cache *cachep, void *objp, int node, int page_node) { @@ -767,7 +777,7 @@ static int __cache_free_alien(struct kmem_cache *cachep, void *objp, STATS_INC_ACOVERFLOW(cachep); __drain_alien_cache(cachep, ac, page_node, &list); } - ac->entry[ac->avail++] = objp; + __free_one(ac, objp); spin_unlock(&alien->lock); slabs_destroy(cachep, &list); } else { @@ -3457,7 +3467,7 @@ void ___cache_free(struct kmem_cache *cachep, void *objp, } } - ac->entry[ac->avail++] = objp; + __free_one(ac, objp); } /**
Similar to commit ce6fa91b9363 ("mm/slub.c: add a naive detection of double free or corruption"), add a very cheap double-free check for SLAB under CONFIG_SLAB_FREELIST_HARDENED. With this added, the "SLAB_FREE_DOUBLE" LKDTM test passes under SLAB: lkdtm: Performing direct entry SLAB_FREE_DOUBLE lkdtm: Attempting double slab free ... ------------[ cut here ]------------ WARNING: CPU: 2 PID: 2193 at mm/slab.c:757 ___cache _free+0x325/0x390 Signed-off-by: Kees Cook <keescook@chromium.org> --- mm/slab.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-)