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Message-ID: <cdb047f0-c071-3263-0167-e9bce852b5d5@huawei.com>
Date: Thu, 6 Apr 2023 20:14:52 +0800
From: Zhihao Cheng <chengzhihao1@...wei.com>
To: ZhaoLong Wang <wangzhaolong1@...wei.com>, <richard@....at>,
<miquel.raynal@...tlin.com>, <vigneshr@...com>
CC: <linux-mtd@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
<yi.zhang@...wei.com>
Subject: Re: [PATCH 1/2] ubi: fix slab-out-of-bounds in
ubi_eba_get_ldesc+0xfb/0x130
HI,
> From: Guo Xuenan <guoxuenan@...wei.com>
>
> When using ioctl interface to resize ubi volume, ubi_resize_volume will
> resize eba table first, but not change vol->reserved_pebs in the same
> atomic context which may cause concurrency access eba table.
>
> For example, When user do shrink ubi volume A calling ubi_resize_volume,
> while the other thread is writing (volume B) and triggering wear-leveling,
> which may calling ubi_write_fastmap, under these circumstances, KASAN may
> report: slab-out-of-bounds in ubi_eba_get_ldesc+0xfb/0x130.
>
[...]
> diff --git a/drivers/mtd/ubi/vmt.c b/drivers/mtd/ubi/vmt.c
> index 2c867d16f89f..97294def01eb 100644
> --- a/drivers/mtd/ubi/vmt.c
> +++ b/drivers/mtd/ubi/vmt.c
> @@ -408,6 +408,7 @@ int ubi_resize_volume(struct ubi_volume_desc *desc, int reserved_pebs)
> struct ubi_device *ubi = vol->ubi;
> struct ubi_vtbl_record vtbl_rec;
> struct ubi_eba_table *new_eba_tbl = NULL;
> + struct ubi_eba_table *old_eba_tbl = NULL;
> int vol_id = vol->vol_id;
>
> if (ubi->ro_mode)
> @@ -453,10 +454,13 @@ int ubi_resize_volume(struct ubi_volume_desc *desc, int reserved_pebs)
> err = -ENOSPC;
> goto out_free;
> }
> +
> ubi->avail_pebs -= pebs;
> ubi->rsvd_pebs += pebs;
> ubi_eba_copy_table(vol, new_eba_tbl, vol->reserved_pebs);
> - ubi_eba_replace_table(vol, new_eba_tbl);
> + old_eba_tbl = vol->eba_tbl;
> + vol->eba_tbl = new_eba_tbl;
> + vol->reserved_pebs = reserved_pebs;
> spin_unlock(&ubi->volumes_lock);
> }
>
> @@ -471,7 +475,9 @@ int ubi_resize_volume(struct ubi_volume_desc *desc, int reserved_pebs)
> ubi->avail_pebs -= pebs;
> ubi_update_reserved(ubi);
> ubi_eba_copy_table(vol, new_eba_tbl, reserved_pebs);
> - ubi_eba_replace_table(vol, new_eba_tbl);
> + old_eba_tbl = vol->eba_tbl;
> + vol->eba_tbl = new_eba_tbl;
> + vol->reserved_pebs = reserved_pebs;
> spin_unlock(&ubi->volumes_lock);
> }
>
> @@ -493,7 +499,6 @@ int ubi_resize_volume(struct ubi_volume_desc *desc, int reserved_pebs)
> if (err)
> goto out_acc;
>
> - vol->reserved_pebs = reserved_pebs;
> if (vol->vol_type == UBI_DYNAMIC_VOLUME) {
> vol->used_ebs = reserved_pebs;
> vol->last_eb_bytes = vol->usable_leb_size;
> @@ -501,19 +506,24 @@ int ubi_resize_volume(struct ubi_volume_desc *desc, int reserved_pebs)
> (long long)vol->used_ebs * vol->usable_leb_size;
> }
>
> + /* destroy old table */
> + ubi_eba_destroy_table(old_eba_tbl);
> ubi_volume_notify(ubi, vol, UBI_VOLUME_RESIZED);
> self_check_volumes(ubi);
> return err;
>
> out_acc:
> + spin_lock(&ubi->volumes_lock);
> + vol->reserved_pebs = reserved_pebs - pebs;
> if (pebs > 0) {
> - spin_lock(&ubi->volumes_lock);
> ubi->rsvd_pebs -= pebs;
> ubi->avail_pebs += pebs;
> - spin_unlock(&ubi->volumes_lock);
> + ubi_eba_copy_table(vol, old_eba_tbl, vol->reserved_pebs);
> + } else {
> + ubi_eba_copy_table(vol, old_eba_tbl, reserved_pebs);
> }
> - return err;
> -
> + vol->eba_tbl = old_eba_tbl;
> + spin_unlock(&ubi->volumes_lock);
> out_free:
> ubi_eba_destroy_table(new_eba_tbl);
> return err;
>
Besides that, it's better to protect 'vol->eba_tbl->entries' assignment
like:
diff --git a/drivers/mtd/ubi/eba.c b/drivers/mtd/ubi/eba.c
index 403b79d6efd5..5ae0c1bc6f41 100644
--- a/drivers/mtd/ubi/eba.c
+++ b/drivers/mtd/ubi/eba.c
@@ -1450,7 +1450,9 @@ int ubi_eba_copy_leb(struct ubi_device *ubi, int
from, int to,
}
ubi_assert(vol->eba_tbl->entries[lnum].pnum == from);
+ spin_lock(&ubi->volumes_lock);
vol->eba_tbl->entries[lnum].pnum = to;
+ spin_unlock(&ubi->volumes_lock);
out_unlock_buf:
mutex_unlock(&ubi->buf_mutex);
Otherwise, a race between wear_leveling_work and shrinking volume could
happen:
ubi_resize_volume wear_leveling_worker
ubi_eba_copy_table(vol, new_eba_tbl, reserved_pebs);
vol->eba_tbl->entries[lnum].pnum = to; //
update old eba_tbl
vol->eba_tbl = new_eba_tbl
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