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author | Eric Biggers <ebiggers@google.com> | 2021-12-20 16:41:56 -0600 |
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committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2022-01-27 09:04:12 +0100 |
commit | a6f8ba674655f511bbf0e55d4f16c581f7a8a35a (patch) | |
tree | 268a99eca04222c548a2baa3fa93da99ce462596 | |
parent | 6332e925ee257e2362be5a6943b9e85b138a2fe9 (diff) | |
download | linux-stable-a6f8ba674655f511bbf0e55d4f16c581f7a8a35a.tar.gz linux-stable-a6f8ba674655f511bbf0e55d4f16c581f7a8a35a.tar.bz2 linux-stable-a6f8ba674655f511bbf0e55d4f16c581f7a8a35a.zip |
random: fix data race on crng_node_pool
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>
-rw-r--r-- | drivers/char/random.c | 42 |
1 files changed, 22 insertions, 20 deletions
diff --git a/drivers/char/random.c b/drivers/char/random.c index 297a716f5a56..5464b928d322 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -831,8 +831,8 @@ 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); @@ -845,8 +845,26 @@ 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 /* @@ -995,15 +1013,7 @@ 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); } /* @@ -1032,15 +1042,7 @@ 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) |