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 B639D3C062; Thu, 1 Aug 2024 19:46:37 +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=1722541597; cv=none; b=kCjkz51GTeOToNh7DfXQ1wd5Uqxt8TL/Nrxl2AegHyH+F8Q+KHJ5ku1XnOvMAXOgADIjK6qPXBrQQ6D4M0GxjYEMw4NflzxBUb0yugyEQVaSQUqwWNrdA2NN81lVld/suhVU1I9lg+fGbrmqIwuCSNK5UL9nt2n5ZpvyoXif6ME= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722541597; c=relaxed/simple; bh=cvgVp/KFbBa9VY7EcJnmpHK375fkBr0I622XMeQskDI=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=rNN+g4OeZhnunhNaQ9LwP80FP54jzkcC71d2aBuxk1HPk5xV14JQ4JMgtEjMOPAqYnD++IjdJdMugrojlFDEBrbn/AYjno7DHIbOXkKZF9GVlRo1JqcjXvkwNe9mrtDhmzerKO5w6VECyB34sACWOIhQBgie12bs+uadmH+CGjk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ly2BxRyZ; 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="ly2BxRyZ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6D92EC4AF0B; Thu, 1 Aug 2024 19:46:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1722541597; bh=cvgVp/KFbBa9VY7EcJnmpHK375fkBr0I622XMeQskDI=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=ly2BxRyZPEA2WhuS5aeULjLcrVRgIQiQ/DX4zYpvRGtul/Be966RQUjgTIKVTzUqN DKGC8UcuiIv1V6A1Wgg+GOSo/+ZbxonDM+wbUOhM2/bNOtwZN176t2tozyaQ2hqaTB E2ycr4r9RSY2YSp1QodQC3/MhtVi1oca+LPEM+7wL3vArGY17OT7FMsSrlCbgGHO4c F5VxBygl3fncV/270frR2Kj7cgqZGpOYiSkmVFUcfhRdLac4ZkRdeCLo5LbJ/ldpEc e4EVoEWZn/4ofmD15/yELMcWCB1Sl+Ffch/8EpY/6i2YdCdQCpzsvKyckO5pv0SUAR mTd89DDib68tw== Message-ID: <9290a079840812e1e8616484ba0a9910d15fe730.camel@kernel.org> Subject: Re: [PATCH RFC v3 2/2] fhandle: expose u64 mount id to name_to_handle_at(2) From: Jeff Layton To: Aleksa Sarai , Alexander Viro , Christian Brauner , Jan Kara , Chuck Lever , Amir Goldstein , Alexander Aring , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Namhyung Kim , Mark Rutland , Alexander Shishkin , Jiri Olsa , Ian Rogers , Adrian Hunter Cc: linux-fsdevel@vger.kernel.org, linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, linux-perf-users@vger.kernel.org Date: Thu, 01 Aug 2024 15:46:34 -0400 In-Reply-To: <20240801-exportfs-u64-mount-id-v3-2-be5d6283144a@cyphar.com> References: <20240801-exportfs-u64-mount-id-v3-0-be5d6283144a@cyphar.com> <20240801-exportfs-u64-mount-id-v3-2-be5d6283144a@cyphar.com> Autocrypt: addr=jlayton@kernel.org; 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charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.50.4 (3.50.4-1.fc39) Precedence: bulk X-Mailing-List: linux-perf-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Thu, 2024-08-01 at 13:52 +1000, Aleksa Sarai wrote: > Now that we provide a unique 64-bit mount ID interface in statx(2), we > can now provide a race-free way for name_to_handle_at(2) to provide a > file handle and corresponding mount without needing to worry about > racing with /proc/mountinfo parsing or having to open a file just to do > statx(2). >=20 > While this is not necessary if you are using AT_EMPTY_PATH and don't > care about an extra statx(2) call, users that pass full paths into > name_to_handle_at(2) need to know which mount the file handle comes from > (to make sure they don't try to open_by_handle_at a file handle from a > different filesystem) and switching to AT_EMPTY_PATH would require > allocating a file for every name_to_handle_at(2) call, turning >=20 > =C2=A0 err =3D name_to_handle_at(-EBADF, "/foo/bar/baz", &handle, &mntid, > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0 AT_HANDLE_MNT_ID_UNIQUE); >=20 > into >=20 > =C2=A0 int fd =3D openat(-EBADF, "/foo/bar/baz", O_PATH | O_CLOEXEC); > =C2=A0 err1 =3D name_to_handle_at(fd, "", &handle, &unused_mntid, AT_EMPT= Y_PATH); > =C2=A0 err2 =3D statx(fd, "", AT_EMPTY_PATH, STATX_MNT_ID_UNIQUE, &statxb= uf); > =C2=A0 mntid =3D statxbuf.stx_mnt_id; > =C2=A0 close(fd); >=20 > Signed-off-by: Aleksa Sarai > --- > =C2=A0fs/fhandle.c=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0 | 29 ++++++++++++++++------ > =C2=A0include/linux/syscalls.h=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 |=C2=A0 2 +- > =C2=A0include/uapi/linux/fcntl.h=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 |=C2=A0 1 + > =C2=A0tools/perf/trace/beauty/include/uapi/linux/fcntl.h |=C2=A0 1 + > =C2=A04 files changed, 25 insertions(+), 8 deletions(-) >=20 > diff --git a/fs/fhandle.c b/fs/fhandle.c > index 6e8cea16790e..8cb665629f4a 100644 > --- a/fs/fhandle.c > +++ b/fs/fhandle.c > @@ -16,7 +16,8 @@ > =C2=A0 > =C2=A0static long do_sys_name_to_handle(const struct path *path, > =C2=A0 =C2=A0 struct file_handle __user *ufh, > - =C2=A0 int __user *mnt_id, int fh_flags) > + =C2=A0 void __user *mnt_id, bool unique_mntid, > + =C2=A0 int fh_flags) > =C2=A0{ > =C2=A0 long retval; > =C2=A0 struct file_handle f_handle; > @@ -69,9 +70,19 @@ static long do_sys_name_to_handle(const struct path *p= ath, > =C2=A0 } else > =C2=A0 retval =3D 0; > =C2=A0 /* copy the mount id */ > - if (put_user(real_mount(path->mnt)->mnt_id, mnt_id) || > - =C2=A0=C2=A0=C2=A0 copy_to_user(ufh, handle, > - struct_size(handle, f_handle, handle_bytes))) > + if (unique_mntid) { > + if (put_user(real_mount(path->mnt)->mnt_id_unique, > + =C2=A0=C2=A0=C2=A0=C2=A0 (u64 __user *) mnt_id)) > + retval =3D -EFAULT; > + } else { > + if (put_user(real_mount(path->mnt)->mnt_id, > + =C2=A0=C2=A0=C2=A0=C2=A0 (int __user *) mnt_id)) > + retval =3D -EFAULT; > + } > + /* copy the handle */ > + if (retval !=3D -EFAULT && > + copy_to_user(ufh, handle, > + =C2=A0=C2=A0=C2=A0=C2=A0 struct_size(handle, f_handle, handle_bytes))= ) > =C2=A0 retval =3D -EFAULT; > =C2=A0 kfree(handle); > =C2=A0 return retval; > @@ -83,6 +94,7 @@ static long do_sys_name_to_handle(const struct path *pa= th, > =C2=A0 * @name: name that should be converted to handle. > =C2=A0 * @handle: resulting file handle > =C2=A0 * @mnt_id: mount id of the file system containing the file > + *=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 (u64 if AT_HAND= LE_MNT_ID_UNIQUE, otherwise int) > =C2=A0 * @flag: flag value to indicate whether to follow symlink or not > =C2=A0 *=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 and whether a decodabl= e file handle is required. > =C2=A0 * > @@ -92,7 +104,7 @@ static long do_sys_name_to_handle(const struct path *p= ath, > =C2=A0 * value required. > =C2=A0 */ > =C2=A0SYSCALL_DEFINE5(name_to_handle_at, int, dfd, const char __user *, n= ame, > - struct file_handle __user *, handle, int __user *, mnt_id, > + struct file_handle __user *, handle, void __user *, mnt_id, > =C2=A0 int, flag) > =C2=A0{ > =C2=A0 struct path path; > @@ -100,7 +112,8 @@ SYSCALL_DEFINE5(name_to_handle_at, int, dfd, const ch= ar __user *, name, > =C2=A0 int fh_flags; > =C2=A0 int err; > =C2=A0 > - if (flag & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH | AT_HANDLE_FID)) > + if (flag & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH | AT_HANDLE_FID | > + =C2=A0=C2=A0=C2=A0=C2=A0 AT_HANDLE_MNT_ID_UNIQUE)) > =C2=A0 return -EINVAL; > =C2=A0 > =C2=A0 lookup_flags =3D (flag & AT_SYMLINK_FOLLOW) ? LOOKUP_FOLLOW : 0; > @@ -109,7 +122,9 @@ SYSCALL_DEFINE5(name_to_handle_at, int, dfd, const ch= ar __user *, name, > =C2=A0 lookup_flags |=3D LOOKUP_EMPTY; > =C2=A0 err =3D user_path_at(dfd, name, lookup_flags, &path); > =C2=A0 if (!err) { > - err =3D do_sys_name_to_handle(&path, handle, mnt_id, fh_flags); > + err =3D do_sys_name_to_handle(&path, handle, mnt_id, > + =C2=A0=C2=A0=C2=A0 flag & AT_HANDLE_MNT_ID_UNIQUE, > + =C2=A0=C2=A0=C2=A0 fh_flags); > =C2=A0 path_put(&path); > =C2=A0 } > =C2=A0 return err; > diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h > index 4bcf6754738d..5758104921e6 100644 > --- a/include/linux/syscalls.h > +++ b/include/linux/syscalls.h > @@ -870,7 +870,7 @@ asmlinkage long sys_fanotify_mark(int fanotify_fd, un= signed int flags, > =C2=A0#endif > =C2=A0asmlinkage long sys_name_to_handle_at(int dfd, const char __user *n= ame, > =C2=A0 =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 struct file_handle __user *handl= e, > - =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 int __user *mnt_id, int flag); > + =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 void __user *mnt_id, int flag); > =C2=A0asmlinkage long sys_open_by_handle_at(int mountdirfd, > =C2=A0 =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 struct file_handle __user *handl= e, > =C2=A0 =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 int flags); > diff --git a/include/uapi/linux/fcntl.h b/include/uapi/linux/fcntl.h > index 38a6d66d9e88..87e2dec79fea 100644 > --- a/include/uapi/linux/fcntl.h > +++ b/include/uapi/linux/fcntl.h > @@ -152,6 +152,7 @@ > =C2=A0#define AT_HANDLE_FID 0x200 /* File handle is needed to compare > =C2=A0 =C2=A0=C2=A0 object identity and may not be > =C2=A0 =C2=A0=C2=A0 usable with open_by_handle_at(2). */ > +#define AT_HANDLE_MNT_ID_UNIQUE 0x001 /* Return the u64 unique mount ID.= */ > =C2=A0 > =C2=A0#if defined(__KERNEL__) > =C2=A0#define AT_GETATTR_NOSEC 0x80000000 > diff --git a/tools/perf/trace/beauty/include/uapi/linux/fcntl.h b/tools/p= erf/trace/beauty/include/uapi/linux/fcntl.h > index 38a6d66d9e88..87e2dec79fea 100644 > --- a/tools/perf/trace/beauty/include/uapi/linux/fcntl.h > +++ b/tools/perf/trace/beauty/include/uapi/linux/fcntl.h > @@ -152,6 +152,7 @@ > =C2=A0#define AT_HANDLE_FID 0x200 /* File handle is needed to compare > =C2=A0 =C2=A0=C2=A0 object identity and may not be > =C2=A0 =C2=A0=C2=A0 usable with open_by_handle_at(2). */ > +#define AT_HANDLE_MNT_ID_UNIQUE 0x001 /* Return the u64 unique mount ID.= */ > =C2=A0 > =C2=A0#if defined(__KERNEL__) > =C2=A0#define AT_GETATTR_NOSEC 0x80000000 >=20 Reviewed-by: Jeff Layton