linux-kernel - [PATCH] nilfs2: protect references to superblock parameters exposed in sysfs

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Message-Id: <20240811100320.9913-1-konishi.ryusuke@gmail.com>
Date: Sun, 11 Aug 2024 19:03:20 +0900
From: Ryusuke Konishi <konishi.ryusuke@...il.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-nilfs@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] nilfs2: protect references to superblock parameters exposed in sysfs

The superblock buffers of nilfs2 can not only be overwritten at
runtime for modifications/repairs, but they are also regularly
swapped, replaced during resizing, and even abandoned when degrading
to one side due to backing device issues.  So, accessing them requires
mutual exclusion using the reader/writer semaphore "nilfs->ns_sem".

Some sysfs attribute show methods read this superblock buffer without
the necessary mutual exclusion, which can cause problems with pointer
dereferencing and memory access, so fix it.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@...il.com>
Fixes: da7141fb78db ("nilfs2: add /sys/fs/nilfs2/<device> group")
Cc: stable@...r.kernel.org
---
Andrew, please apply this as a bug fix.

This fixes possible memory access problem when retrieving superblock
information from the sysfs interface.

Thanks,
Ryusuke Konishi

 fs/nilfs2/sysfs.c | 43 +++++++++++++++++++++++++++++++++----------
 1 file changed, 33 insertions(+), 10 deletions(-)

diff --git a/fs/nilfs2/sysfs.c b/fs/nilfs2/sysfs.c
index a5569b7f47a3..14868a3dd592 100644
--- a/fs/nilfs2/sysfs.c
+++ b/fs/nilfs2/sysfs.c
@@ -836,9 +836,15 @@ ssize_t nilfs_dev_revision_show(struct nilfs_dev_attr *attr,
 				struct the_nilfs *nilfs,
 				char *buf)
 {
-	struct nilfs_super_block **sbp = nilfs->ns_sbp;
-	u32 major = le32_to_cpu(sbp[0]->s_rev_level);
-	u16 minor = le16_to_cpu(sbp[0]->s_minor_rev_level);
+	struct nilfs_super_block *raw_sb;
+	u32 major;
+	u16 minor;
+
+	down_read(&nilfs->ns_sem);
+	raw_sb = nilfs->ns_sbp[0];
+	major = le32_to_cpu(raw_sb->s_rev_level);
+	minor = le16_to_cpu(raw_sb->s_minor_rev_level);
+	up_read(&nilfs->ns_sem);
 
 	return sysfs_emit(buf, "%d.%d\n", major, minor);
 }
@@ -856,8 +862,13 @@ ssize_t nilfs_dev_device_size_show(struct nilfs_dev_attr *attr,
 				    struct the_nilfs *nilfs,
 				    char *buf)
 {
-	struct nilfs_super_block **sbp = nilfs->ns_sbp;
-	u64 dev_size = le64_to_cpu(sbp[0]->s_dev_size);
+	struct nilfs_super_block *raw_sb;
+	u64 dev_size;
+
+	down_read(&nilfs->ns_sem);
+	raw_sb = nilfs->ns_sbp[0];
+	dev_size = le64_to_cpu(raw_sb->s_dev_size);
+	up_read(&nilfs->ns_sem);
 
 	return sysfs_emit(buf, "%llu\n", dev_size);
 }
@@ -879,9 +890,15 @@ ssize_t nilfs_dev_uuid_show(struct nilfs_dev_attr *attr,
 			    struct the_nilfs *nilfs,
 			    char *buf)
 {
-	struct nilfs_super_block **sbp = nilfs->ns_sbp;
+	struct nilfs_super_block *raw_sb;
+	ssize_t len;
 
-	return sysfs_emit(buf, "%pUb\n", sbp[0]->s_uuid);
+	down_read(&nilfs->ns_sem);
+	raw_sb = nilfs->ns_sbp[0];
+	len = sysfs_emit(buf, "%pUb\n", raw_sb->s_uuid);
+	up_read(&nilfs->ns_sem);
+
+	return len;
 }
 
 static
@@ -889,10 +906,16 @@ ssize_t nilfs_dev_volume_name_show(struct nilfs_dev_attr *attr,
 				    struct the_nilfs *nilfs,
 				    char *buf)
 {
-	struct nilfs_super_block **sbp = nilfs->ns_sbp;
+	struct nilfs_super_block *raw_sb;
+	ssize_t len;
+
+	down_read(&nilfs->ns_sem);
+	raw_sb = nilfs->ns_sbp[0];
+	len = scnprintf(buf, sizeof(raw_sb->s_volume_name), "%s\n",
+			raw_sb->s_volume_name);
+	up_read(&nilfs->ns_sem);
 
-	return scnprintf(buf, sizeof(sbp[0]->s_volume_name), "%s\n",
-			 sbp[0]->s_volume_name);
+	return len;
 }
 
 static const char dev_readme_str[] =
-- 
2.34.1