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Wed, 26 Jun 2019 09:28:35 -0700 Date: Wed, 26 Jun 2019 09:28:31 -0700 From: "Darrick J. Wong" To: Al Viro Message-ID: <20190626162831.GF5171@magnolia> References: <156151637248.2283603.8458727861336380714.stgit@magnolia> <156151641177.2283603.7806026378321236401.stgit@magnolia> <20190626035151.GA10613@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20190626035151.GA10613@ZenIV.linux.org.uk> User-Agent: Mutt/1.9.4 (2018-02-28) X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9300 signatures=668687 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1906260193 X-Headers-End: 1hgApv-00B7pa-7U Subject: Re: [f2fs-dev] [PATCH 5/5] vfs: don't allow writes to swap files X-BeenThere: linux-f2fs-devel@lists.sourceforge.net X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-efi@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-mm@kvack.org, clm@fb.com, adilger.kernel@dilger.ca, matthew.garrett@nebula.com, linux-nilfs@vger.kernel.org, hch@infradead.org, linux-ext4@vger.kernel.org, devel@lists.orangefs.org, josef@toxicpanda.com, reiserfs-devel@vger.kernel.org, dsterba@suse.com, jaegeuk@kernel.org, tytso@mit.edu, ard.biesheuvel@linaro.org, linux-kernel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, linux-xfs@vger.kernel.org, jk@ozlabs.org, jack@suse.com, linux-fsdevel@vger.kernel.org, linux-mtd@lists.infradead.org, ocfs2-devel@oss.oracle.com Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: linux-f2fs-devel-bounces@lists.sourceforge.net On Wed, Jun 26, 2019 at 04:51:51AM +0100, Al Viro wrote: > On Tue, Jun 25, 2019 at 07:33:31PM -0700, Darrick J. Wong wrote: > > --- a/fs/attr.c > > +++ b/fs/attr.c > > @@ -236,6 +236,9 @@ int notify_change(struct dentry * dentry, struct iattr * attr, struct inode **de > > if (IS_IMMUTABLE(inode)) > > return -EPERM; > > > > + if (IS_SWAPFILE(inode)) > > + return -ETXTBSY; > > + > > if ((ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID | ATTR_TIMES_SET)) && > > IS_APPEND(inode)) > > return -EPERM; > > Er... So why exactly is e.g. chmod(2) forbidden for swapfiles? Or touch(1), > for that matter... Oops, that check is overly broad; I think the only attribute change we need to filter here is ATTR_SIZE.... which we could do unconditionally in inode_newsize_ok. What's the use case for allowing userspace to increase the size of an active swapfile? I don't see any; the kernel has a permanent lease on the file space mapping (at least until swapoff)... > > diff --git a/mm/swapfile.c b/mm/swapfile.c > > index 596ac98051c5..1ca4ee8c2d60 100644 > > --- a/mm/swapfile.c > > +++ b/mm/swapfile.c > > @@ -3165,6 +3165,19 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags) > > if (error) > > goto bad_swap; > > > > + /* > > + * Flush any pending IO and dirty mappings before we start using this > > + * swap file. > > + */ > > + if (S_ISREG(inode->i_mode)) { > > + inode->i_flags |= S_SWAPFILE; > > + error = inode_drain_writes(inode); > > + if (error) { > > + inode->i_flags &= ~S_SWAPFILE; > > + goto bad_swap; > > + } > > + } > > Why are swap partitions any less worthy of protection? Hmm, yeah, S_SWAPFILE should apply to block devices too. I figured that the mantra of "sane tools will open block devices with O_EXCL" should have sufficed, but there's really no reason to allow that either. --D _______________________________________________ Linux-f2fs-devel mailing list Linux-f2fs-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel