[PATCH 2/2] acct: block access to kernel internal filesystems

[Christian Brauner]

There's no point in allowing anything kernel internal nor procfs or
sysfs.

Reported-by: Zicheng Qu <quzicheng@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20250127091811.3183623-1-quzicheng@xxxxxxxxxx
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Christian Brauner <brauner@xxxxxxxxxx>
---
 kernel/acct.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/kernel/acct.c b/kernel/acct.c
index 48283efe8a12..6520baa13669 100644
--- a/kernel/acct.c
+++ b/kernel/acct.c
@@ -243,6 +243,20 @@ static int acct_on(struct filename *pathname)
 		return -EACCES;
 	}
 
+	/* Exclude kernel kernel internal filesystems. */
+	if (file_inode(file)->i_sb->s_flags & (SB_NOUSER | SB_KERNMOUNT)) {
+		kfree(acct);
+		filp_close(file, NULL);
+		return -EINVAL;
+	}
+
+	/* Exclude procfs and sysfs. */
+	if (file_inode(file)->i_sb->s_iflags & SB_I_USERNS_VISIBLE) {
+		kfree(acct);
+		filp_close(file, NULL);
+		return -EINVAL;
+	}
+
 	if (!(file->f_mode & FMODE_CAN_WRITE)) {
 		kfree(acct);
 		filp_close(file, NULL);

-- 
2.47.2