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Received: from willy by casper.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1vRrm9-00000007BhE-1GZr; Sat, 06 Dec 2025 12:52:37 +0000 Date: Sat, 6 Dec 2025 12:52:37 +0000 From: Matthew Wilcox To: Ahelenia =?utf-8?Q?Ziemia=C5=84ska?= Cc: Andrew Morton , Hugh Dickins , Baolin Wang , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] tmpfs: enforce the immutable flag on open files Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 51D56A000D X-Stat-Signature: m6xnp5pgkq4jmcbtf41j8b98761ibhgz X-Rspam-User: X-HE-Tag: 1765025563-563079 X-HE-Meta: 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 eIkKdmgU cPFaQGW0anQ0yXFziN9jXr9wlJm+3wLSBYevFjOoATUunvbHFmtH3Sw0pcxty1WXPxRGvQJ3XtSXNSuvfUTQKHaiV1yFQkl0GCziDWYyBfjmitgzUMZ4KinYy5GnBJkwSFl7hyalVBa7r0gS8YNZ55fIOLlwflkueOLuCPjm1L9GgXf+PiWVm1zP+RZ2RnJqSvLcfPr/rwM4GIYoAnf1tBnfjTUGqYJqc3FYXho/jdx0T/F9ud+TJJSpmM4C1FqNMrmwlg09zTR+QVxhmt6P0dGNprA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sat, Dec 06, 2025 at 01:03:35PM +0100, Ahelenia Ziemiańska wrote: > diff --git a/mm/filemap.c b/mm/filemap.c > index ebd75684cb0a..0b0d5cfbcd44 100644 > --- a/mm/filemap.c > +++ b/mm/filemap.c > @@ -3945,12 +3945,18 @@ EXPORT_SYMBOL(filemap_map_pages); > > vm_fault_t filemap_page_mkwrite(struct vm_fault *vmf) > { > - struct address_space *mapping = vmf->vma->vm_file->f_mapping; > + struct file *file = vmf->vma->vm_file; > + struct address_space *mapping = file->f_mapping; > struct folio *folio = page_folio(vmf->page); > vm_fault_t ret = VM_FAULT_LOCKED; > > + if (unlikely(IS_IMMUTABLE(file_inode(file)))) { > + ret = VM_FAULT_SIGBUS; > + goto out; I don't believe you tested this code path. It contains a rather obvious bug. > + } > + > sb_start_pagefault(mapping->host->i_sb); > - file_update_time(vmf->vma->vm_file); > + file_update_time(file); > folio_lock(folio); > if (folio->mapping != mapping) { > folio_unlock(folio); > diff --git a/mm/shmem.c b/mm/shmem.c > index d578d8e765d7..5d3fbf4efb3d 100644 > --- a/mm/shmem.c > +++ b/mm/shmem.c > @@ -1294,6 +1294,14 @@ static int shmem_setattr(struct mnt_idmap *idmap, > bool update_mtime = false; > bool update_ctime = true; > > + if (unlikely(IS_IMMUTABLE(inode))) > + return -EPERM; > + > + if (unlikely(IS_APPEND(inode) && > + (attr->ia_valid & (ATTR_MODE | ATTR_UID | > + ATTR_GID | ATTR_TIMES_SET)))) > + return -EPERM; > + > error = setattr_prepare(idmap, dentry, attr); > if (error) > return error; > @@ -3475,6 +3483,10 @@ static ssize_t shmem_file_write_iter(struct kiocb *iocb, struct iov_iter *from) > ret = generic_write_checks(iocb, from); > if (ret <= 0) > goto unlock; > + if (unlikely(IS_IMMUTABLE(inode))) { > + ret = -EPERM; > + goto unlock; > + } > ret = file_remove_privs(file); > if (ret) > goto unlock; > -- > 2.39.5