ext4: enforce the immutable flag on open files

BugLink: https://bugs.launchpad.net/bugs/1839036
commit 02b016ca7f99229ae6227e7b2fc950c4e140d74a upstream.

According to the chattr man page, "a file with the 'i' attribute
cannot be modified..."  Historically, this was only enforced when the
file was opened, per the rest of the description, "... and the file
can not be opened in write mode".

There is general agreement that we should standardize all file systems
to prevent modifications even for files that were opened at the time
the immutable flag is set.  Eventually, a change to enforce this at
the VFS layer should be landing in mainline.  Until then, enforce this
at the ext4 level to prevent xfstests generic/553 from failing.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: "Darrick J. Wong" <darrick.wong@oracle.com>
Cc: stable@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index 5a6a503a952375b9d9c0fe014e2f3e8ac660cece..8d8558e570e0496a3c4960052a2ca964e78bce77 100644 (file)
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -165,6 +165,10 @@ static ssize_t ext4_write_checks(struct kiocb *iocb, struct iov_iter *from)
        ret = generic_write_checks(iocb, from);
        if (ret <= 0)
                return ret;
+
+       if (unlikely(IS_IMMUTABLE(inode)))
+               return -EPERM;
+
        /*
         * If we have encountered a bitmap-format file, the size limit
         * is smaller than s_maxbytes, which is for extent-mapped files.

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index ba08864341c1068b59d9f7ff4fc41c66b1f7ac2c..89a418a53aa71cc815060c6f5813f3f6d93f6ae0 100644 (file)
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -5427,6 +5427,14 @@ int ext4_setattr(struct dentry *dentry, struct iattr *attr)
        if (unlikely(ext4_forced_shutdown(EXT4_SB(inode->i_sb))))
                return -EIO;
 
+       if (unlikely(IS_IMMUTABLE(inode)))
+               return -EPERM;
+
+       if (unlikely(IS_APPEND(inode) &&
+                    (ia_valid & (ATTR_MODE | ATTR_UID |
+                                 ATTR_GID | ATTR_TIMES_SET))))
+               return -EPERM;
+
        error = setattr_prepare(dentry, attr);
        if (error)
                return error;
@@ -6122,6 +6130,9 @@ int ext4_page_mkwrite(struct vm_fault *vmf)
        get_block_t *get_block;
        int retries = 0;
 
+       if (unlikely(IS_IMMUTABLE(inode)))
+               return VM_FAULT_SIGBUS;
+
        sb_start_pagefault(inode->i_sb);
        file_update_time(vma->vm_file);