acct: block access to kernel internal filesystems

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

Link: https://lore.kernel.org/r/20250127091811.3183623-1-quzicheng@huawei.com
Link: https://lore.kernel.org/r/20250211-work-acct-v1-2-1c16aecab8b3@kernel.org
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Reported-by: Zicheng Qu <quzicheng@huawei.com>
Cc: stable@vger.kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/kernel/acct.c b/kernel/acct.c
index 48283efe8a1231512691146f76b0573b7fa35132..6520baa13669391174b4b86430649e4e90321834 100644 (file)
--- 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);