From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8661F3803CD; Thu, 29 Jan 2026 12:33:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769690039; cv=none; b=bj5eI8dNN9pAX0s+5x3z4FH5/ZKLhYwoorQufj8U6YqaYrCyOxNTKeMTF10HcBT5On2nliPaiJJ+KcoLXrpyb4MNsT6rHSEsDeCZnHvuOtlaKfIDh3tlqsfGCllhpIWBEx9+v+fBdUx2hHyY7vQ2duihgt3NMvWJumvfxUIjy60= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769690039; c=relaxed/simple; bh=T8LVKAlG2mPj51Ja7GkX2ymwn24dcWsRdg6iMR6aEpI=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ZypCvGXuNzbhVm2nIjNqDGLnXgJ7NkqN4F44cexXXgoqMqCvFCIKXgIxlHRexvGvk1/D9jC4G/lCVQMXE9V3LjsojVmdAEOV45T53wplGBKQkYsE20QSFT0hFtWAEzBlkG0520pdQToru6KtI/kDdgyw4dKss59cgc+fGBPm+R4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=rEi2QULl; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="rEi2QULl" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A9C1FC4CEF7; Thu, 29 Jan 2026 12:33:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1769690039; bh=T8LVKAlG2mPj51Ja7GkX2ymwn24dcWsRdg6iMR6aEpI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=rEi2QULlowEU+wI8AfywhHuJvH3ONnbnSAgBNe7kreU6GeEsNv0kgjc3AtF5Q+41W IgQYqOpZnI5t/xYNE0DwlnijUPmtruFFPxVy6/rQSPW8EoFekSa+ks/X24DP5L09zM yXCco1hr5M9o3eZSc90njSV01KOMsthGqkvEOHBSt/U2do/+lr2cExf76CcxjfKSrf MUe38DjbYQkuh/3f+vjRv9IHz6TnPPdJquJ0OvVtXD+GMx4gXfCChIG9E5ECnNtzCV vFRLZ57Px/rUodxoay3MA7o+HGkhfSZU746nqyYT9dS54dJctRgB0gNUmybUlGEHKi 8Jb//y6dOQadw== Date: Thu, 29 Jan 2026 13:33:54 +0100 From: Christian Brauner To: Jeff Layton Cc: Dorjoy Chowdhury , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk, jack@suse.cz, chuck.lever@oracle.com, alex.aring@gmail.com, arnd@arndb.de, adilger@dilger.ca Subject: Re: [PATCH v3 1/4] open: new O_REGULAR flag support Message-ID: <20260129-tierwelt-wahlabend-2cb470bcb707@brauner> References: <20260127180109.66691-1-dorjoychy111@gmail.com> <20260127180109.66691-2-dorjoychy111@gmail.com> <1c6cccc3e058ef16fa8b296ef6126b76a12db136.camel@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Wed, Jan 28, 2026 at 10:51:07AM -0500, Jeff Layton wrote: > On Wed, 2026-01-28 at 21:36 +0600, Dorjoy Chowdhury wrote: > > On Wed, Jan 28, 2026 at 5:52 AM Jeff Layton wrote: > > > > > > On Tue, 2026-01-27 at 23:58 +0600, Dorjoy Chowdhury wrote: > > > > This flag indicates the path should be opened if it's a regular file. > > > > This is useful to write secure programs that want to avoid being tricked > > > > into opening device nodes with special semantics while thinking they > > > > operate on regular files. > > > > > > > > A corresponding error code ENOTREG has been introduced. For example, if > > > > open is called on path /dev/null with O_REGULAR in the flag param, it > > > > will return -ENOTREG. > > > > > > > > When used in combination with O_CREAT, either the regular file is > > > > created, or if the path already exists, it is opened if it's a regular > > > > file. Otherwise, -ENOTREG is returned. > > > > > > > > -EINVAL is returned when O_REGULAR is combined with O_DIRECTORY (not > > > > part of O_TMPFILE) because it doesn't make sense to open a path that > > > > is both a directory and a regular file. > > > > > > > > Signed-off-by: Dorjoy Chowdhury > > > > --- > > > > arch/alpha/include/uapi/asm/errno.h | 2 ++ > > > > arch/alpha/include/uapi/asm/fcntl.h | 1 + > > > > arch/mips/include/uapi/asm/errno.h | 2 ++ > > > > arch/parisc/include/uapi/asm/errno.h | 2 ++ > > > > arch/parisc/include/uapi/asm/fcntl.h | 1 + > > > > arch/sparc/include/uapi/asm/errno.h | 2 ++ > > > > arch/sparc/include/uapi/asm/fcntl.h | 1 + > > > > fs/fcntl.c | 2 +- > > > > fs/namei.c | 6 ++++++ > > > > fs/open.c | 4 +++- > > > > include/linux/fcntl.h | 2 +- > > > > include/uapi/asm-generic/errno.h | 2 ++ > > > > include/uapi/asm-generic/fcntl.h | 4 ++++ > > > > tools/arch/alpha/include/uapi/asm/errno.h | 2 ++ > > > > tools/arch/mips/include/uapi/asm/errno.h | 2 ++ > > > > tools/arch/parisc/include/uapi/asm/errno.h | 2 ++ > > > > tools/arch/sparc/include/uapi/asm/errno.h | 2 ++ > > > > tools/include/uapi/asm-generic/errno.h | 2 ++ > > > > 18 files changed, 38 insertions(+), 3 deletions(-) > > > > > > > > diff --git a/arch/alpha/include/uapi/asm/errno.h b/arch/alpha/include/uapi/asm/errno.h > > > > index 6791f6508632..8bbcaa9024f9 100644 > > > > --- a/arch/alpha/include/uapi/asm/errno.h > > > > +++ b/arch/alpha/include/uapi/asm/errno.h > > > > @@ -127,4 +127,6 @@ > > > > > > > > #define EHWPOISON 139 /* Memory page has hardware error */ > > > > > > > > +#define ENOTREG 140 /* Not a regular file */ > > > > + > > > > #endif > > > > diff --git a/arch/alpha/include/uapi/asm/fcntl.h b/arch/alpha/include/uapi/asm/fcntl.h > > > > index 50bdc8e8a271..4da5a64c23bd 100644 > > > > --- a/arch/alpha/include/uapi/asm/fcntl.h > > > > +++ b/arch/alpha/include/uapi/asm/fcntl.h > > > > @@ -34,6 +34,7 @@ > > > > > > > > #define O_PATH 040000000 > > > > #define __O_TMPFILE 0100000000 > > > > +#define O_REGULAR 0200000000 > > > > > > > > #define F_GETLK 7 > > > > #define F_SETLK 8 > > > > diff --git a/arch/mips/include/uapi/asm/errno.h b/arch/mips/include/uapi/asm/errno.h > > > > index c01ed91b1ef4..293c78777254 100644 > > > > --- a/arch/mips/include/uapi/asm/errno.h > > > > +++ b/arch/mips/include/uapi/asm/errno.h > > > > @@ -126,6 +126,8 @@ > > > > > > > > #define EHWPOISON 168 /* Memory page has hardware error */ > > > > > > > > +#define ENOTREG 169 /* Not a regular file */ > > > > + > > > > #define EDQUOT 1133 /* Quota exceeded */ > > > > > > > > > > > > diff --git a/arch/parisc/include/uapi/asm/errno.h b/arch/parisc/include/uapi/asm/errno.h > > > > index 8cbc07c1903e..442917484f99 100644 > > > > --- a/arch/parisc/include/uapi/asm/errno.h > > > > +++ b/arch/parisc/include/uapi/asm/errno.h > > > > @@ -124,4 +124,6 @@ > > > > > > > > #define EHWPOISON 257 /* Memory page has hardware error */ > > > > > > > > +#define ENOTREG 258 /* Not a regular file */ > > > > + > > > > #endif > > > > diff --git a/arch/parisc/include/uapi/asm/fcntl.h b/arch/parisc/include/uapi/asm/fcntl.h > > > > index 03dee816cb13..0cc3320fe326 100644 > > > > --- a/arch/parisc/include/uapi/asm/fcntl.h > > > > +++ b/arch/parisc/include/uapi/asm/fcntl.h > > > > @@ -19,6 +19,7 @@ > > > > > > > > #define O_PATH 020000000 > > > > #define __O_TMPFILE 040000000 > > > > +#define O_REGULAR 0100000000 > > > > > > > > #define F_GETLK64 8 > > > > #define F_SETLK64 9 > > > > diff --git a/arch/sparc/include/uapi/asm/errno.h b/arch/sparc/include/uapi/asm/errno.h > > > > index 4a41e7835fd5..8dce0bfeab74 100644 > > > > --- a/arch/sparc/include/uapi/asm/errno.h > > > > +++ b/arch/sparc/include/uapi/asm/errno.h > > > > @@ -117,4 +117,6 @@ > > > > > > > > #define EHWPOISON 135 /* Memory page has hardware error */ > > > > > > > > +#define ENOTREG 136 /* Not a regular file */ > > > > + > > > > #endif > > > > diff --git a/arch/sparc/include/uapi/asm/fcntl.h b/arch/sparc/include/uapi/asm/fcntl.h > > > > index 67dae75e5274..a93d18d2c23e 100644 > > > > --- a/arch/sparc/include/uapi/asm/fcntl.h > > > > +++ b/arch/sparc/include/uapi/asm/fcntl.h > > > > @@ -37,6 +37,7 @@ > > > > > > > > #define O_PATH 0x1000000 > > > > #define __O_TMPFILE 0x2000000 > > > > +#define O_REGULAR 0x4000000 > > > > > > > > #define F_GETOWN 5 /* for sockets. */ > > > > #define F_SETOWN 6 /* for sockets. */ > > > > diff --git a/fs/fcntl.c b/fs/fcntl.c > > > > index f93dbca08435..62ab4ad2b6f5 100644 > > > > --- a/fs/fcntl.c > > > > +++ b/fs/fcntl.c > > > > @@ -1169,7 +1169,7 @@ static int __init fcntl_init(void) > > > > * Exceptions: O_NONBLOCK is a two bit define on parisc; O_NDELAY > > > > * is defined as O_NONBLOCK on some platforms and not on others. > > > > */ > > > > - BUILD_BUG_ON(20 - 1 /* for O_RDONLY being 0 */ != > > > > + BUILD_BUG_ON(21 - 1 /* for O_RDONLY being 0 */ != > > > > HWEIGHT32( > > > > (VALID_OPEN_FLAGS & ~(O_NONBLOCK | O_NDELAY)) | > > > > __FMODE_EXEC)); > > > > diff --git a/fs/namei.c b/fs/namei.c > > > > index b28ecb699f32..f5504ae4b03c 100644 > > > > --- a/fs/namei.c > > > > +++ b/fs/namei.c > > > > @@ -4616,6 +4616,10 @@ static int do_open(struct nameidata *nd, > > > > if (unlikely(error)) > > > > return error; > > > > } > > > > + > > > > + if ((open_flag & O_REGULAR) && !d_is_reg(nd->path.dentry)) > > > > + return -ENOTREG; > > > > + > > > > if ((nd->flags & LOOKUP_DIRECTORY) && !d_can_lookup(nd->path.dentry)) > > > > return -ENOTDIR; > > > > > > > > @@ -4765,6 +4769,8 @@ static int do_o_path(struct nameidata *nd, unsigned flags, struct file *file) > > > > struct path path; > > > > int error = path_lookupat(nd, flags, &path); > > > > if (!error) { > > > > + if ((file->f_flags & O_REGULAR) && !d_is_reg(path.dentry)) > > > > + return -ENOTREG; > > > > audit_inode(nd->name, path.dentry, 0); > > > > error = vfs_open(&path, file); > > > > path_put(&path); > > > > diff --git a/fs/open.c b/fs/open.c > > > > index 74c4c1462b3e..82153e21907e 100644 > > > > --- a/fs/open.c > > > > +++ b/fs/open.c > > > > @@ -1173,7 +1173,7 @@ struct file *kernel_file_open(const struct path *path, int flags, > > > > EXPORT_SYMBOL_GPL(kernel_file_open); > > > > > > > > #define WILL_CREATE(flags) (flags & (O_CREAT | __O_TMPFILE)) > > > > -#define O_PATH_FLAGS (O_DIRECTORY | O_NOFOLLOW | O_PATH | O_CLOEXEC) > > > > +#define O_PATH_FLAGS (O_DIRECTORY | O_NOFOLLOW | O_PATH | O_CLOEXEC | O_REGULAR) > > > > > > > > inline struct open_how build_open_how(int flags, umode_t mode) > > > > { > > > > @@ -1250,6 +1250,8 @@ inline int build_open_flags(const struct open_how *how, struct open_flags *op) > > > > return -EINVAL; > > > > if (!(acc_mode & MAY_WRITE)) > > > > return -EINVAL; > > > > + } else if ((flags & O_DIRECTORY) && (flags & O_REGULAR)) { > > > > + return -EINVAL; > > > > } > > > > if (flags & O_PATH) { > > > > /* O_PATH only permits certain other flags to be set. */ > > > > diff --git a/include/linux/fcntl.h b/include/linux/fcntl.h > > > > index a332e79b3207..4fd07b0e0a17 100644 > > > > --- a/include/linux/fcntl.h > > > > +++ b/include/linux/fcntl.h > > > > @@ -10,7 +10,7 @@ > > > > (O_RDONLY | O_WRONLY | O_RDWR | O_CREAT | O_EXCL | O_NOCTTY | O_TRUNC | \ > > > > O_APPEND | O_NDELAY | O_NONBLOCK | __O_SYNC | O_DSYNC | \ > > > > FASYNC | O_DIRECT | O_LARGEFILE | O_DIRECTORY | O_NOFOLLOW | \ > > > > - O_NOATIME | O_CLOEXEC | O_PATH | __O_TMPFILE) > > > > + O_NOATIME | O_CLOEXEC | O_PATH | __O_TMPFILE | O_REGULAR) > > > > > > > > /* List of all valid flags for the how->resolve argument: */ > > > > #define VALID_RESOLVE_FLAGS \ > > > > diff --git a/include/uapi/asm-generic/errno.h b/include/uapi/asm-generic/errno.h > > > > index 92e7ae493ee3..2216ab9aa32e 100644 > > > > --- a/include/uapi/asm-generic/errno.h > > > > +++ b/include/uapi/asm-generic/errno.h > > > > @@ -122,4 +122,6 @@ > > > > > > > > #define EHWPOISON 133 /* Memory page has hardware error */ > > > > > > > > +#define ENOTREG 134 /* Not a regular file */ > > > > + > > > > #endif > > > > diff --git a/include/uapi/asm-generic/fcntl.h b/include/uapi/asm-generic/fcntl.h > > > > index 613475285643..3468b352a575 100644 > > > > --- a/include/uapi/asm-generic/fcntl.h > > > > +++ b/include/uapi/asm-generic/fcntl.h > > > > @@ -88,6 +88,10 @@ > > > > #define __O_TMPFILE 020000000 > > > > #endif > > > > > > > > +#ifndef O_REGULAR > > > > +#define O_REGULAR 040000000 > > > > +#endif > > > > + > > > > /* a horrid kludge trying to make sure that this will fail on old kernels */ > > > > #define O_TMPFILE (__O_TMPFILE | O_DIRECTORY) > > > > > > > > diff --git a/tools/arch/alpha/include/uapi/asm/errno.h b/tools/arch/alpha/include/uapi/asm/errno.h > > > > index 6791f6508632..8bbcaa9024f9 100644 > > > > --- a/tools/arch/alpha/include/uapi/asm/errno.h > > > > +++ b/tools/arch/alpha/include/uapi/asm/errno.h > > > > @@ -127,4 +127,6 @@ > > > > > > > > #define EHWPOISON 139 /* Memory page has hardware error */ > > > > > > > > +#define ENOTREG 140 /* Not a regular file */ > > > > + > > > > #endif > > > > diff --git a/tools/arch/mips/include/uapi/asm/errno.h b/tools/arch/mips/include/uapi/asm/errno.h > > > > index c01ed91b1ef4..293c78777254 100644 > > > > --- a/tools/arch/mips/include/uapi/asm/errno.h > > > > +++ b/tools/arch/mips/include/uapi/asm/errno.h > > > > @@ -126,6 +126,8 @@ > > > > > > > > #define EHWPOISON 168 /* Memory page has hardware error */ > > > > > > > > +#define ENOTREG 169 /* Not a regular file */ > > > > + > > > > #define EDQUOT 1133 /* Quota exceeded */ > > > > > > > > > > > > diff --git a/tools/arch/parisc/include/uapi/asm/errno.h b/tools/arch/parisc/include/uapi/asm/errno.h > > > > index 8cbc07c1903e..442917484f99 100644 > > > > --- a/tools/arch/parisc/include/uapi/asm/errno.h > > > > +++ b/tools/arch/parisc/include/uapi/asm/errno.h > > > > @@ -124,4 +124,6 @@ > > > > > > > > #define EHWPOISON 257 /* Memory page has hardware error */ > > > > > > > > +#define ENOTREG 258 /* Not a regular file */ > > > > + > > > > #endif > > > > diff --git a/tools/arch/sparc/include/uapi/asm/errno.h b/tools/arch/sparc/include/uapi/asm/errno.h > > > > index 4a41e7835fd5..8dce0bfeab74 100644 > > > > --- a/tools/arch/sparc/include/uapi/asm/errno.h > > > > +++ b/tools/arch/sparc/include/uapi/asm/errno.h > > > > @@ -117,4 +117,6 @@ > > > > > > > > #define EHWPOISON 135 /* Memory page has hardware error */ > > > > > > > > +#define ENOTREG 136 /* Not a regular file */ > > > > + > > > > #endif > > > > diff --git a/tools/include/uapi/asm-generic/errno.h b/tools/include/uapi/asm-generic/errno.h > > > > index 92e7ae493ee3..2216ab9aa32e 100644 > > > > --- a/tools/include/uapi/asm-generic/errno.h > > > > +++ b/tools/include/uapi/asm-generic/errno.h > > > > @@ -122,4 +122,6 @@ > > > > > > > > #define EHWPOISON 133 /* Memory page has hardware error */ > > > > > > > > +#define ENOTREG 134 /* Not a regular file */ > > > > + > > > > #endif > > > > > > One thing this patch is missing is handling for ->atomic_open(). I > > > imagine most of the filesystems that provide that op can't support > > > O_REGULAR properly (maybe cifs can? idk). What you probably want to do > > > is add in some patches that make all of the atomic_open operations in > > > the kernel return -EINVAL if O_REGULAR is set. > > > > > > Then, once the basic support is in, you or someone else can go back and > > > implement support for O_REGULAR where possible. > > > > Thank you for the feedback. I don't quite understand what I need to > > fix. I thought open system calls always create regular files, so > > atomic_open probably always creates regular files? Can you please give > > me some more details as to where I need to fix this and what the > > actual bug here is that is related to atomic_open? I think I had done > > some normal testing and when using O_CREAT | O_REGULAR, if the file > > doesn't exist, the file gets created and the file that gets created is > > a regular file, so it probably makes sense? Or should the behavior be > > that if file doesn't exist, -EINVAL is returned and if file exists it > > is opened if regular, otherwise -ENOTREG is returned? > > > > atomic_open() is a combination lookup+open for when the dentry isn't > present in the dcache. The normal open codepath that you're patching > does not get called in this case when ->atomic_open is set for the > filesystem. It's mostly used by network filesystems that need to > optimize away the lookup since it's wasted round trip, and is often > racy anyway. Your patchset doesn't address those filesystems. They will > likely end up ignoring O_REGULAR in that case, which is not what you > want. > > What I was suggesting is that, as an interim step, you find all of the > atomic_open operations in the kernel (there are maybe a dozen or so), > and just make them return -EINVAL if someone sets O_DIRECTORY. Later, > you or someone else can then go back and do a proper implementation of > O_REGULAR handling on those filesystems, at least on the ones where > it's possible. You will probably also need to similarly patch the > open() routines for those filesystems too. Otherwise you'll get > inconsistent behavior vs. when the dentry is in the cache. > > One note: I think NFS probably can support O_DIRECTORY, since its OPEN > call only works on files. We'll need to change how we handle errors > from the server when it's set though. So I think you're proposing two separate things or there's a typo: (1) blocking O_DIRECTORY for ->atomic_open:: (2) blocking O_REGULAR for ->atomic_open:: The (1) point implies that O_DIRECTORY currently doesn't work correctly with atomic open for all filesystems. Ever since 43b450632676 ("open: return EINVAL for O_DIRECTORY | O_CREAT") O_DIRECTORY with O_CREAT is blocked. It was accidently allowed and completely broken before that. For O_DIRECTORY without O_CREAT the kernel will pass that down through ->atomic_open:: to the filesystem. The worry that I see is that a network filesystem via ->atomic_open:: somehow already called open on the server side on something that wasn't a directory. At that point the damage such as side-effects from device opening is already done. But I suspect that every filesystem implementing ->atomic_open:: just does finish_no_open() and punts to the VFS for the actual open. And the VFS will catch it in do_open() for it actually opens the file. So the only real worry for O_DIRECTORY I see is that there's an fs that handles it wrong. For (2) it is problematic as there surely are filesystems with ->atomic_open:: that do handle the ~O_CREAT case and return with FMODE_OPENED. So that'll be problematic if the intention is to not trigger an actual open on a non-regular file such as a device/socket/fifo etc. before the VFS had a chance to validate what's going on. So I'm not excited about having this 70% working and punting on ->atomic_open:: waiting for someone to fix this. One option would be to bypass ->atomic_open:: for OPENAT2_REGULAR without O_CREAT and fallback to racy and pricy lookup + open for now. How problematic would that be? If possible I'd prefer this a lot over merging something that works half-way. I guess to make that really work you'd need some protocol extension?