[PATCH 6.6 123/140] acct: block access to kernel internal filesystems

[Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>]

6.6-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Christian Brauner <brauner@xxxxxxxxxx>

commit 890ed45bde808c422c3c27d3285fc45affa0f930 upstream.

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

Link: https://lore.kernel.org/r/20250127091811.3183623-1-quzicheng@xxxxxxxxxx
Link: https://lore.kernel.org/r/20250211-work-acct-v1-2-1c16aecab8b3@xxxxxxxxxx
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reviewed-by: Amir Goldstein <amir73il@xxxxxxxxx>
Reported-by: Zicheng Qu <quzicheng@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Christian Brauner <brauner@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 kernel/acct.c |   14 ++++++++++++++
 1 file changed, 14 insertions(+)

--- a/kernel/acct.c
+++ b/kernel/acct.c
@@ -244,6 +244,20 @@ static int acct_on(struct filename *path
 		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);