This patch fixes a bug in the freelist randomization code. When a high
random number is used, the freelist will contain duplicate entries. It
will result in different allocations sharing the same chunk.
Fixes: c7ce4f60ac19 ("mm: SLAB freelist randomization")
Signed-off-by: John Sperbeck <jsperb...@google.com>
Reviewed-by: Thomas Garnier <thgar...@google.com>
---
mm/slab.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/mm/slab.c b/mm/slab.c
index 29bc6c0dedd0..4f2ec6bb46eb 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -2457,7 +2457,6 @@ union freelist_init_state {
unsigned int pos;
unsigned int *list;
unsigned int count;
- unsigned int rand;
};
struct rnd_state rnd_state;
};
@@ -2483,8 +2482,7 @@ static bool freelist_state_initialize(union
freelist_init_state *state,
} else {
state->list = cachep->random_seq;
state->count = count;
- state->pos = 0;
- state->rand = rand;
+ state->pos = rand % count;
ret = true;
}
return ret;
@@ -2493,7 +2491,9 @@ static bool freelist_state_initialize(union
freelist_init_state *state,
/* Get the next entry on the list and randomize it using a random shift */
static freelist_idx_t next_random_slot(union freelist_init_state *state)
{
- return (state->list[state->pos++] + state->rand) % state->count;
+ if (state->pos >= state->count)
+ state->pos = 0;
+ return state->list[state->pos++];
}
/* Swap two freelist entries */
--
2.11.0.390.gc69c2f50cf-goog
