From: Eric Biggers ebiggers@google.com
stable inclusion from stable-v4.19.226 commit a6f8ba674655f511bbf0e55d4f16c581f7a8a35a category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/I7BZ5U CVE: NA
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commit 5d73d1e320c3fd94ea15ba5f79301da9a8bcc7de upstream.
extract_crng() and crng_backtrack_protect() load crng_node_pool with a plain load, which causes undefined behavior if do_numa_crng_init() modifies it concurrently.
Fix this by using READ_ONCE(). Note: as per the previous discussion https://lore.kernel.org/lkml/20211219025139.31085-1-ebiggers@kernel.org/T/#u, READ_ONCE() is believed to be sufficient here, and it was requested that it be used here instead of smp_load_acquire().
Also change do_numa_crng_init() to set crng_node_pool using cmpxchg_release() instead of mb() + cmpxchg(), as the former is sufficient here but is more lightweight.
Fixes: 1e7f583af67b ("random: make /dev/urandom scalable for silly userspace programs") Cc: stable@vger.kernel.org Signed-off-by: Eric Biggers ebiggers@google.com Acked-by: Paul E. McKenney paulmck@kernel.org Signed-off-by: Jason A. Donenfeld Jason@zx2c4.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: GONG, Ruiqi gongruiqi@huaweicloud.com Reviewed-by: Wang Weiyang wangweiyang2@huawei.com Reviewed-by: Xiu Jianfeng xiujianfeng@huawei.com Signed-off-by: Yongqiang Liu liuyongqiang13@huawei.com --- drivers/char/random.c | 42 ++++++++++++++++++++++-------------------- 1 file changed, 22 insertions(+), 20 deletions(-)
diff --git a/drivers/char/random.c b/drivers/char/random.c index 05daadfbf1ed..a008d816cf2b 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -836,8 +836,8 @@ static void do_numa_crng_init(struct work_struct *work) crng_initialize(crng); pool[i] = crng; } - mb(); - if (cmpxchg(&crng_node_pool, NULL, pool)) { + /* pairs with READ_ONCE() in select_crng() */ + if (cmpxchg_release(&crng_node_pool, NULL, pool) != NULL) { for_each_node(i) kfree(pool[i]); kfree(pool); @@ -850,8 +850,26 @@ static void numa_crng_init(void) { schedule_work(&numa_crng_init_work); } + +static struct crng_state *select_crng(void) +{ + struct crng_state **pool; + int nid = numa_node_id(); + + /* pairs with cmpxchg_release() in do_numa_crng_init() */ + pool = READ_ONCE(crng_node_pool); + if (pool && pool[nid]) + return pool[nid]; + + return &primary_crng; +} #else static void numa_crng_init(void) {} + +static struct crng_state *select_crng(void) +{ + return &primary_crng; +} #endif
/* @@ -1000,15 +1018,7 @@ static void _extract_crng(struct crng_state *crng,
static void extract_crng(__u8 out[CHACHA20_BLOCK_SIZE]) { - struct crng_state *crng = NULL; - -#ifdef CONFIG_NUMA - if (crng_node_pool) - crng = crng_node_pool[numa_node_id()]; - if (crng == NULL) -#endif - crng = &primary_crng; - _extract_crng(crng, out); + _extract_crng(select_crng(), out); }
/* @@ -1037,15 +1047,7 @@ static void _crng_backtrack_protect(struct crng_state *crng,
static void crng_backtrack_protect(__u8 tmp[CHACHA20_BLOCK_SIZE], int used) { - struct crng_state *crng = NULL; - -#ifdef CONFIG_NUMA - if (crng_node_pool) - crng = crng_node_pool[numa_node_id()]; - if (crng == NULL) -#endif - crng = &primary_crng; - _crng_backtrack_protect(crng, tmp, used); + _crng_backtrack_protect(select_crng(), tmp, used); }
static ssize_t extract_crng_user(void __user *buf, size_t nbytes)