linux-kernel - [PATCH v2] erofs: avoid using multiple devices with different type

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Message-ID: <20250515014837.3315886-1-shengyong1@xiaomi.com>
Date: Thu, 15 May 2025 09:48:37 +0800
From: Sheng Yong <shengyong2021@...il.com>
To: xiang@...nel.org,
	hsiangkao@...ux.alibaba.com,
	chao@...nel.org,
	zbestahu@...il.com,
	jefflexu@...ux.alibaba.com,
	dhavale@...gle.com,
	lihongbo22@...wei.com
Cc: linux-erofs@...ts.ozlabs.org,
	linux-kernel@...r.kernel.org,
	Sheng Yong <shengyong1@...omi.com>
Subject: [PATCH v2] erofs: avoid using multiple devices with different type

From: Sheng Yong <shengyong1@...omi.com>

For multiple devices, both primary and extra devices should be the
same type. `erofs_init_device` has already guaranteed that if the
primary is a file-backed device, extra devices should also be
regular files.

However, if the primary is a block device while the extra device
is a file-backed device, `erofs_init_device` will get an ENOTBLK,
which is not treated as an error in `erofs_fc_get_tree`, and that
leads to an UAF:

  erofs_fc_get_tree
    get_tree_bdev_flags(erofs_fc_fill_super)
      erofs_read_superblock
        erofs_init_device  // sbi->dif0 is not inited yet,
                           // return -ENOTBLK
      deactivate_locked_super
        free(sbi)
    if (err is -ENOTBLK)
      sbi->dif0.file = filp_open()  // sbi UAF

So if -ENOTBLK is hitted in `erofs_init_device`, it means the
primary device must be a block device, and the extra device
is not a block device. The error can be converted to -EINVAL.

Fixes: fb176750266a ("erofs: add file-backed mount support")
Signed-off-by: Sheng Yong <shengyong1@...omi.com>
---
 fs/erofs/super.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/erofs/super.c b/fs/erofs/super.c
index 512877d7d855..6b998a49b61e 100644
--- a/fs/erofs/super.c
+++ b/fs/erofs/super.c
@@ -165,8 +165,11 @@ static int erofs_init_device(struct erofs_buf *buf, struct super_block *sb,
 				filp_open(dif->path, O_RDONLY | O_LARGEFILE, 0) :
 				bdev_file_open_by_path(dif->path,
 						BLK_OPEN_READ, sb->s_type, NULL);
-		if (IS_ERR(file))
+		if (IS_ERR(file)) {
+			if (file == ERR_PTR(-ENOTBLK))
+				return -EINVAL;
 			return PTR_ERR(file);
+		}
 
 		if (!erofs_is_fileio_mode(sbi)) {
 			dif->dax_dev = fs_dax_get_by_bdev(file_bdev(file),
-- 
2.43.0