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 D557D26158B; Mon, 30 Mar 2026 12:12:38 +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=1774872758; cv=none; b=lDGC8tNrSbJ6UrsPXs7tW6pboOg80qq+cOTblfgVXIkwUUUHrACSd0PSwwVhKwHMw/YeyxRa9Lv3o4AvZaQHd+NH2+ZhZvzg1dm0dRtoJtZUY3fMKpJv0rf3+MBWYGMzetAwGXa7f3VjtNNywCKdRWH+IviSkTtEhks0LDzH9T0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774872758; c=relaxed/simple; bh=yEmrf+JTnTJ95Cv0KoHwIbHQDWbrEQQdV+atXyjYZAc=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=Eu1Unf144NCmLTGEVUsB+aWtAbz7d367JDdVef5Pxryy4cyS/eA9Y0MSI0ihQBlhNtjdCBBLqI87MmqYvPbDWBsTPaub7sc1In7NGbEIfTi1zKcHlYJ4tW3T4OfBboPf8UKyx0YeoRZCtbAFo4dbPkG+L/Kz0RcRaIMeTUZHtSk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=iNdp4K5s; 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="iNdp4K5s" Received: by smtp.kernel.org (Postfix) with ESMTPSA id EAD6DC2BCB0; Mon, 30 Mar 2026 12:12:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1774872758; bh=yEmrf+JTnTJ95Cv0KoHwIbHQDWbrEQQdV+atXyjYZAc=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=iNdp4K5sHwmSPuSETaU/mDyHTxBtdE9IokRxKreRihak7yhcPRwalvjO3ygtPKQAI U2WyiRk7WVlFPEKyYzbSRNLEhIhPf/vHafrT5StPIwr7E9lDkH9c9N9m2yGsRW5G05 7ce8IabAAmaLGWX08lLGIuNEBDOL76KiyIxekzqPgmcjOaKXuuihkSM2VFxs1y7Ufu cWw0I816JIRGh6EYOWz25AX2yxFbdk+nEPa4qSMBHgIIRL8pWM67v4tpHQ4imGJpD+ uEjUh8KB4ClpavZehEPzSQqL9UNEjDHnndTkht1YEICElvrC/gKwYiBIJvDrqVhvl2 iFt8j9HhuUPWQ== Message-ID: Subject: Re: [RFC PATCH v2 1/3] vfs: add support for empty path to openat2(2) From: Jeff Layton To: Jori Koolstra , Chuck Lever , Alexander Aring , Alexander Viro , Christian Brauner , Jan Kara , Shuah Khan , Greg Kroah-Hartman , Aleksa Sarai Cc: Andrew Morton , Mike Rapoport , "Liam R . Howlett" , David Hildenbrand , Lorenzo Stoakes , Ethan Tidmore , NeilBrown , Oleg Nesterov , Penglei Jiang , Kees Cook , Suren Baghdasaryan , Vlastimil Babka , Amir Goldstein , Namjae Jeon , Mateusz Guzik , Wei Yang , Bala-Vignesh-Reddy , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kselftest@vger.kernel.org Date: Mon, 30 Mar 2026 08:12:33 -0400 In-Reply-To: <20260326182033.1809567-2-jkoolstra@xs4all.nl> References: <20260326182033.1809567-1-jkoolstra@xs4all.nl> <20260326182033.1809567-2-jkoolstra@xs4all.nl> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV T2h6v8i8YqsATFPwO4nuiTmL6I40ZofxVd+9wdRI4Db8yUNA4ZSP2nqLcLtFjClYRBoJvRWvsv4lm 0OX6MYPtv76hka8lW4mnRmZqqx3UtfHX/hF/zH24Gj7A6sYKYLCU3YrI2Ogiu7/ksKcl7goQjpvtV 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O_DIRECTORY) for directories, but other files > currently require going through open("/proc//fd/"), which > depends on a functioning procfs. >=20 > This patch adds the OPENAT2_EMPTY_PATH flag to openat2(2). If passed, > LOOKUP_EMPTY is set at path resolve time. >=20 > Note: This implies that you cannot rely anymore on disabling procfs from > being mounted (e.g. inside a container without procfs mounted and with > CAP_SYS_ADMIN dropped) to prevent O_PATH fds from being re-opened > read-write. >=20 > Signed-off-by: Jori Koolstra > --- > fs/fcntl.c | 4 ++-- > fs/open.c | 11 +++++------ > include/linux/fcntl.h | 5 ++++- > include/uapi/linux/openat2.h | 4 ++++ > 4 files changed, 15 insertions(+), 9 deletions(-) >=20 > diff --git a/fs/fcntl.c b/fs/fcntl.c > index beab8080badf..d9ae3c71edfe 100644 > --- a/fs/fcntl.c > +++ b/fs/fcntl.c > @@ -1169,8 +1169,8 @@ 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 */ !=3D > - HWEIGHT32( > + BUILD_BUG_ON(21 - 1 /* for O_RDONLY being 0 */ !=3D > + HWEIGHT64( > (VALID_OPEN_FLAGS & ~(O_NONBLOCK | O_NDELAY)) | > __FMODE_EXEC)); > =20 > diff --git a/fs/open.c b/fs/open.c > index 91f1139591ab..e019ddecc73c 100644 > --- a/fs/open.c > +++ b/fs/open.c > @@ -1160,12 +1160,12 @@ struct file *kernel_file_open(const struct path *= path, int flags, > EXPORT_SYMBOL_GPL(kernel_file_open); > =20 > #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= PENAT2_EMPTY_PATH) > =20 > inline struct open_how build_open_how(int flags, umode_t mode) > { > struct open_how how =3D { > - .flags =3D flags & VALID_OPEN_FLAGS, > + .flags =3D ((unsigned int) flags) & VALID_OPEN_FLAGS, > .mode =3D mode & S_IALLUGO, > }; > =20 > @@ -1185,9 +1185,6 @@ inline int build_open_flags(const struct open_how *= how, struct open_flags *op) > int lookup_flags =3D 0; > int acc_mode =3D ACC_MODE(flags); > =20 > - BUILD_BUG_ON_MSG(upper_32_bits(VALID_OPEN_FLAGS), > - "struct open_flags doesn't yet handle flags > 32 bits"); > - > /* > * Strip flags that aren't relevant in determining struct open_flags. > */ > @@ -1281,6 +1278,8 @@ inline int build_open_flags(const struct open_how *= how, struct open_flags *op) > lookup_flags |=3D LOOKUP_DIRECTORY; > if (!(flags & O_NOFOLLOW)) > lookup_flags |=3D LOOKUP_FOLLOW; > + if (flags & OPENAT2_EMPTY_PATH) > + lookup_flags |=3D LOOKUP_EMPTY; > =20 > if (how->resolve & RESOLVE_NO_XDEV) > lookup_flags |=3D LOOKUP_NO_XDEV; > @@ -1362,7 +1361,7 @@ static int do_sys_openat2(int dfd, const char __use= r *filename, > if (unlikely(err)) > return err; > =20 > - CLASS(filename, name)(filename); > + CLASS(filename_flags, name)(filename, op.lookup_flags); > return FD_ADD(how->flags, do_file_open(dfd, name, &op)); > } > =20 > diff --git a/include/linux/fcntl.h b/include/linux/fcntl.h > index a332e79b3207..d1bb87ff70e3 100644 > --- a/include/linux/fcntl.h > +++ b/include/linux/fcntl.h > @@ -7,10 +7,13 @@ > =20 > /* List of all valid flags for the open/openat flags argument: */ > #define VALID_OPEN_FLAGS \ > + /* lower 32-bit flags */ \ > (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 | \ > + /* upper 32-bit flags (openat2(2) only) */ \ > + OPENAT2_EMPTY_PATH) > =20 > /* List of all valid flags for the how->resolve argument: */ > #define VALID_RESOLVE_FLAGS \ > diff --git a/include/uapi/linux/openat2.h b/include/uapi/linux/openat2.h > index a5feb7604948..c34f32e6fa96 100644 > --- a/include/uapi/linux/openat2.h > +++ b/include/uapi/linux/openat2.h > @@ -40,4 +40,8 @@ struct open_how { > return -EAGAIN if that's not > possible. */ > =20 > +/* openat2(2) exclusive flags are defined in the upper 32 bits of > + open_how->flags */ > +#define OPENAT2_EMPTY_PATH 0x100000000 /* (1ULL << 32) */ > + > #endif /* _UAPI_LINUX_OPENAT2_H */ Looks sane to me. Can this be merged apart from the rest of the series? It doesn't seem like the transitive stuff is dependent on this. Reviewed-by: Jeff Layton