4.9-stable review patch. If anyone has any objections, please let me know.
------------------ From: John Sperbeck <[email protected]> commit c4e490cf148e85ead0d1b1c2caaba833f1d5b29f upstream. 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. It will result in odd behaviours and crashes. It should be uncommon but it depends on the machines. We saw it happening more often on some machines (every few hours of running tests). Fixes: c7ce4f60ac19 ("mm: SLAB freelist randomization") Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: John Sperbeck <[email protected]> Signed-off-by: Thomas Garnier <[email protected]> Cc: Christoph Lameter <[email protected]> Cc: Pekka Enberg <[email protected]> Cc: David Rientjes <[email protected]> Cc: Joonsoo Kim <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]> --- mm/slab.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) --- a/mm/slab.c +++ b/mm/slab.c @@ -2475,7 +2475,6 @@ union freelist_init_state { unsigned int pos; unsigned int *list; unsigned int count; - unsigned int rand; }; struct rnd_state rnd_state; }; @@ -2501,8 +2500,7 @@ static bool freelist_state_initialize(un } else { state->list = cachep->random_seq; state->count = count; - state->pos = 0; - state->rand = rand; + state->pos = rand % count; ret = true; } return ret; @@ -2511,7 +2509,9 @@ static bool freelist_state_initialize(un /* 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 */
