The patch below does not apply to the 5.15-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
Thanks, Sasha
------------------ original commit in Linus's tree ------------------
From dfd2bf436709b2bccb78c2dda550dde93700efa7 Mon Sep 17 00:00:00 2001 From: Gui-Dong Han 2045gemini@gmail.com Date: Fri, 12 Jan 2024 15:10:17 +0800 Subject: [PATCH] md/raid5: fix atomicity violation in raid5_cache_count
In raid5_cache_count(): if (conf->max_nr_stripes < conf->min_nr_stripes) return 0; return conf->max_nr_stripes - conf->min_nr_stripes; The current check is ineffective, as the values could change immediately after being checked.
In raid5_set_cache_size(): ... conf->min_nr_stripes = size; ... while (size > conf->max_nr_stripes) conf->min_nr_stripes = conf->max_nr_stripes; ...
Due to intermediate value updates in raid5_set_cache_size(), concurrent execution of raid5_cache_count() and raid5_set_cache_size() may lead to inconsistent reads of conf->max_nr_stripes and conf->min_nr_stripes. The current checks are ineffective as values could change immediately after being checked, raising the risk of conf->min_nr_stripes exceeding conf->max_nr_stripes and potentially causing an integer overflow.
This possible bug is found by an experimental static analysis tool developed by our team. This tool analyzes the locking APIs to extract function pairs that can be concurrently executed, and then analyzes the instructions in the paired functions to identify possible concurrency bugs including data races and atomicity violations. The above possible bug is reported when our tool analyzes the source code of Linux 6.2.
To resolve this issue, it is suggested to introduce local variables 'min_stripes' and 'max_stripes' in raid5_cache_count() to ensure the values remain stable throughout the check. Adding locks in raid5_cache_count() fails to resolve atomicity violations, as raid5_set_cache_size() may hold intermediate values of conf->min_nr_stripes while unlocked. With this patch applied, our tool no longer reports the bug, with the kernel configuration allyesconfig for x86_64. Due to the lack of associated hardware, we cannot test the patch in runtime testing, and just verify it according to the code logic.
Fixes: edbe83ab4c27 ("md/raid5: allow the stripe_cache to grow and shrink.") Cc: stable@vger.kernel.org Signed-off-by: Gui-Dong Han 2045gemini@gmail.com Reviewed-by: Yu Kuai yukuai3@huawei.com Signed-off-by: Song Liu song@kernel.org Link: https://lore.kernel.org/r/20240112071017.16313-1-2045gemini@gmail.com Signed-off-by: Song Liu song@kernel.org --- drivers/md/raid5.c | 14 ++++++++------ 1 file changed, 8 insertions(+), 6 deletions(-)
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c index 14f2cf75abbd7..7ec445f49f1c3 100644 --- a/drivers/md/raid5.c +++ b/drivers/md/raid5.c @@ -2412,7 +2412,7 @@ static int grow_one_stripe(struct r5conf *conf, gfp_t gfp) atomic_inc(&conf->active_stripes);
raid5_release_stripe(sh); - conf->max_nr_stripes++; + WRITE_ONCE(conf->max_nr_stripes, conf->max_nr_stripes + 1); return 1; }
@@ -2707,7 +2707,7 @@ static int drop_one_stripe(struct r5conf *conf) shrink_buffers(sh); free_stripe(conf->slab_cache, sh); atomic_dec(&conf->active_stripes); - conf->max_nr_stripes--; + WRITE_ONCE(conf->max_nr_stripes, conf->max_nr_stripes - 1); return 1; }
@@ -6820,7 +6820,7 @@ raid5_set_cache_size(struct mddev *mddev, int size) if (size <= 16 || size > 32768) return -EINVAL;
- conf->min_nr_stripes = size; + WRITE_ONCE(conf->min_nr_stripes, size); mutex_lock(&conf->cache_size_mutex); while (size < conf->max_nr_stripes && drop_one_stripe(conf)) @@ -6832,7 +6832,7 @@ raid5_set_cache_size(struct mddev *mddev, int size) mutex_lock(&conf->cache_size_mutex); while (size > conf->max_nr_stripes) if (!grow_one_stripe(conf, GFP_KERNEL)) { - conf->min_nr_stripes = conf->max_nr_stripes; + WRITE_ONCE(conf->min_nr_stripes, conf->max_nr_stripes); result = -ENOMEM; break; } @@ -7388,11 +7388,13 @@ static unsigned long raid5_cache_count(struct shrinker *shrink, struct shrink_control *sc) { struct r5conf *conf = shrink->private_data; + int max_stripes = READ_ONCE(conf->max_nr_stripes); + int min_stripes = READ_ONCE(conf->min_nr_stripes);
- if (conf->max_nr_stripes < conf->min_nr_stripes) + if (max_stripes < min_stripes) /* unlikely, but not impossible */ return 0; - return conf->max_nr_stripes - conf->min_nr_stripes; + return max_stripes - min_stripes; }
static struct r5conf *setup_conf(struct mddev *mddev)