md/md-bitmap: Synchronize bitmap_get_stats() with bitmap lifetime

[ Upstream commit 8d28d0ddb986f56920ac97ae704cc3340a699a30 ]

After commit ec6bb299c7c3 ("md/md-bitmap: add 'sync_size' into struct
md_bitmap_stats"), following panic is reported:

Oops: general protection fault, probably for non-canonical address
RIP: 0010:bitmap_get_stats+0x2b/0xa0
Call Trace:
 <TASK>
 md_seq_show+0x2d2/0x5b0
 seq_read_iter+0x2b9/0x470
 seq_read+0x12f/0x180
 proc_reg_read+0x57/0xb0
 vfs_read+0xf6/0x380
 ksys_read+0x6c/0xf0
 do_syscall_64+0x82/0x170
 entry_SYSCALL_64_after_hwframe+0x76/0x7e

Root cause is that bitmap_get_stats() can be called at anytime if mddev
is still there, even if bitmap is destroyed, or not fully initialized.
Deferenceing bitmap in this case can crash the kernel. Meanwhile, the
above commit start to deferencing bitmap->storage, make the problem
easier to trigger.

Fix the problem by protecting bitmap_get_stats() with bitmap_info.mutex.

Cc: stable@vger.kernel.org # v6.12+
Fixes: 32a7627cf3a3 ("[PATCH] md: optimised resync using Bitmap based intent logging")
Reported-and-tested-by: Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>
Closes: https://lore.kernel.org/linux-raid/ca3a91a2-50ae-4f68-b317-abd9889f3907@oracle.com/T/#m6e5086c95201135e4941fe38f9efa76daf9666c5
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Link: https://lore.kernel.org/r/20250124092055.4050195-1-yukuai1@huaweicloud.com
Signed-off-by: Song Liu <song@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/md/md-bitmap.c b/drivers/md/md-bitmap.c
index 80b0cd7b88995c3667ae484be355bc2799460156..deb40a8ba3999501fba9c6d26cd1dda1e3669218 100644 (file)
--- a/drivers/md/md-bitmap.c
+++ b/drivers/md/md-bitmap.c
@@ -2119,7 +2119,10 @@ int md_bitmap_get_stats(struct bitmap *bitmap, struct md_bitmap_stats *stats)
 
        if (!bitmap)
                return -ENOENT;
-
+       if (bitmap->mddev->bitmap_info.external)
+               return -ENOENT;
+       if (!bitmap->storage.sb_page) /* no superblock */
+               return -EINVAL;
        sb = kmap_local_page(bitmap->storage.sb_page);
        stats->sync_size = le64_to_cpu(sb->sync_size);
        kunmap_local(sb);

diff --git a/drivers/md/md.c b/drivers/md/md.c
index b73649fd8e039e3081ab63e02516c4fdf3f06c80..534c4efd935f6cb97aaa01ebecfda859dfcc046c 100644 (file)
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -8327,6 +8327,10 @@ static int md_seq_show(struct seq_file *seq, void *v)
                return 0;
 
        spin_unlock(&all_mddevs_lock);
+
+       /* prevent bitmap to be freed after checking */
+       mutex_lock(&mddev->bitmap_info.mutex);
+
        spin_lock(&mddev->lock);
        if (mddev->pers || mddev->raid_disks || !list_empty(&mddev->disks)) {
                seq_printf(seq, "%s : %sactive", mdname(mddev),
@@ -8397,6 +8401,7 @@ static int md_seq_show(struct seq_file *seq, void *v)
                seq_printf(seq, "\n");
        }
        spin_unlock(&mddev->lock);
+       mutex_unlock(&mddev->bitmap_info.mutex);
        spin_lock(&all_mddevs_lock);
        if (atomic_dec_and_test(&mddev->active))
                __mddev_put(mddev);