From: Aleksa Sarai <cyphar@cyphar.com>
To: Al Viro <viro@zeniv.linux.org.uk>,
Jeff Layton <jlayton@kernel.org>,
"J. Bruce Fields" <bfields@fieldses.org>,
Arnd Bergmann <arnd@arndb.de>,
David Howells <dhowells@redhat.com>,
Shuah Khan <shuah@kernel.org>,
Shuah Khan <skhan@linuxfoundation.org>
Cc: Aleksa Sarai <cyphar@cyphar.com>,
Eric Biederman <ebiederm@xmission.com>,
Andy Lutomirski <luto@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Alexei Starovoitov <ast@kernel.org>,
Kees Cook <keescook@chromium.org>, Jann Horn <jannh@google.com>,
Christian Brauner <christian@brauner.io>,
Tycho Andersen <tycho@tycho.ws>,
David Drysdale <drysdale@google.com>,
Chanho Min <chanho.min@lge.com>, Oleg Nesterov <oleg@redhat.com>,
Aleksa Sarai <asarai@suse.de>,
Linus Torvalds <torvalds@linux-foundation.org>,
containers@lists.linux-foundation.org,
linux-alpha@vger.kernel.org, linux-api@vger.kernel.org,
linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
linux-fsdevel@vger.kernel.org, linux-ia64@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org,
linux-m68k@lists.linux-m68k.org, linux-mips@vger.kernel.org,
linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
linux-s390@vger.kernel.org, linux-sh@vger.kernel.org,
linux-xtensa@linux-xtensa.org, sparclinux@vger.kernel.org
Subject: [PATCH v9 03/10] open: O_EMPTYPATH: procfs-less file descriptor re-opening
Date: Sun, 7 Jul 2019 00:57:30 +1000 [thread overview]
Message-ID: <20190706145737.5299-4-cyphar@cyphar.com> (raw)
In-Reply-To: <20190706145737.5299-1-cyphar@cyphar.com>
Userspace has made use of /proc/self/fd very liberally to allow for
descriptors to be re-opened. There are a wide variety of uses for this
feature, but it has always required constructing a pathname and could
not be done without procfs mounted. The obvious solution for this is to
extend openat(2) to have an AT_EMPTY_PATH-equivalent -- O_EMPTYPATH.
Now that descriptor re-opening has been made safe through the new
magic-link resolution restrictions, we can replicate these restrictions
for O_EMPTYPATH. In particular, we only allow "upgrading" the file
descriptor if the corresponding FMODE_PATH_* bit is set (or the
FMODE_{READ,WRITE} cases for non-O_PATH file descriptors).
When doing openat(O_EMPTYPATH|O_PATH), O_PATH takes precedence and
O_EMPTYPATH is ignored. Very few users ever have a need to O_PATH
re-open an existing file descriptor, and so accommodating them at the
expense of further complicating O_PATH makes little sense. Ultimately,
if users ask for this we can always add RESOLVE_EMPTY_PATH to
resolveat(2) in the future.
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
---
fs/fcntl.c | 2 +-
fs/namei.c | 27 +++++++++++++++++++++++++++
fs/open.c | 7 ++++++-
include/linux/fcntl.h | 2 +-
include/uapi/asm-generic/fcntl.h | 5 +++++
5 files changed, 40 insertions(+), 3 deletions(-)
diff --git a/fs/fcntl.c b/fs/fcntl.c
index 3d40771e8e7c..4cf05a2fd162 100644
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -1031,7 +1031,7 @@ 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(21 - 1 /* for O_RDONLY being 0 */ !=
+ BUILD_BUG_ON(22 - 1 /* for O_RDONLY being 0 */ !=
HWEIGHT32(
(VALID_OPEN_FLAGS & ~(O_NONBLOCK | O_NDELAY)) |
__FMODE_EXEC | __FMODE_NONOTIFY));
diff --git a/fs/namei.c b/fs/namei.c
index 4ec6168762db..4895717d2760 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -3605,6 +3605,31 @@ static int do_o_path(struct nameidata *nd, unsigned flags, struct file *file)
return error;
}
+static int do_o_emptypath(struct nameidata *nd, struct file *newfile)
+{
+ int error;
+ struct fd f;
+
+ /* We don't support AT_FDCWD since O_PATH cannot be set here. */
+ f = fdget_raw(nd->dfd);
+ if (!f.file)
+ return -EBADF;
+
+ /* Update opath_mask as though we went through trailing_symlink(). */
+ if (!(f.file->f_mode & (FMODE_READ | FMODE_PATH_READ)))
+ nd->opath_mask &= ~FMODE_PATH_READ;
+ if (!(f.file->f_mode & (FMODE_WRITE | FMODE_PATH_WRITE)))
+ nd->opath_mask &= ~FMODE_PATH_WRITE;
+
+ /* Obey the same restrictions as magic-links. */
+ error = may_open_magiclink(f.file->f_mode, nd->acc_mode);
+ if (!error)
+ error = vfs_open(&f.file->f_path, newfile);
+
+ fdput(f);
+ return error;
+}
+
static struct file *path_openat(struct nameidata *nd,
const struct open_flags *op, unsigned flags)
{
@@ -3620,6 +3645,8 @@ static struct file *path_openat(struct nameidata *nd,
if (unlikely(file->f_flags & __O_TMPFILE)) {
error = do_tmpfile(nd, flags, op, file);
+ } else if (unlikely(file->f_flags & O_EMPTYPATH)) {
+ error = do_o_emptypath(nd, file);
} else if (unlikely(file->f_flags & O_PATH)) {
error = do_o_path(nd, flags, file);
} else {
diff --git a/fs/open.c b/fs/open.c
index ab20eae39df7..bdca45528524 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -996,6 +996,8 @@ static inline int build_open_flags(int flags, umode_t mode, struct open_flags *o
lookup_flags |= LOOKUP_DIRECTORY;
if (!(flags & O_NOFOLLOW))
lookup_flags |= LOOKUP_FOLLOW;
+ if (flags & O_EMPTYPATH)
+ lookup_flags |= LOOKUP_EMPTY;
op->lookup_flags = lookup_flags;
return 0;
}
@@ -1057,14 +1059,17 @@ long do_sys_open(int dfd, const char __user *filename, int flags, umode_t mode)
{
struct open_flags op;
int fd = build_open_flags(flags, mode, &op);
+ int empty = 0;
struct filename *tmp;
if (fd)
return fd;
- tmp = getname(filename);
+ tmp = getname_flags(filename, op.lookup_flags, &empty);
if (IS_ERR(tmp))
return PTR_ERR(tmp);
+ if (!empty)
+ op.open_flag &= ~O_EMPTYPATH;
fd = get_unused_fd_flags(flags);
if (fd >= 0) {
diff --git a/include/linux/fcntl.h b/include/linux/fcntl.h
index d019df946cb2..2868ae6c8fc1 100644
--- a/include/linux/fcntl.h
+++ b/include/linux/fcntl.h
@@ -9,7 +9,7 @@
(O_RDONLY | O_WRONLY | O_RDWR | O_CREAT | O_EXCL | O_NOCTTY | O_TRUNC | \
O_APPEND | O_NDELAY | O_NONBLOCK | O_NDELAY | __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_EMPTYPATH)
#ifndef force_o_largefile
#define force_o_largefile() (!IS_ENABLED(CONFIG_ARCH_32BIT_OFF_T))
diff --git a/include/uapi/asm-generic/fcntl.h b/include/uapi/asm-generic/fcntl.h
index 9dc0bf0c5a6e..307f7c414a51 100644
--- a/include/uapi/asm-generic/fcntl.h
+++ b/include/uapi/asm-generic/fcntl.h
@@ -89,6 +89,11 @@
#define __O_TMPFILE 020000000
#endif
+#ifndef O_EMPTYPATH
+#define O_EMPTYPATH 040000000
+#endif
+
+
/* a horrid kludge trying to make sure that this will fail on old kernels */
#define O_TMPFILE (__O_TMPFILE | O_DIRECTORY)
#define O_TMPFILE_MASK (__O_TMPFILE | O_DIRECTORY | O_CREAT)
--
2.22.0
next prev parent reply other threads:[~2019-07-06 14:59 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-06 14:57 [PATCH v9 00/10] namei: openat2(2) path resolution restrictions Aleksa Sarai
2019-07-06 14:57 ` [PATCH v9 01/10] namei: obey trailing magic-link DAC permissions Aleksa Sarai
2019-07-12 4:14 ` Al Viro
2019-07-12 6:36 ` Al Viro
2019-07-12 12:20 ` Aleksa Sarai
2019-07-12 13:10 ` Al Viro
2019-07-14 7:11 ` Aleksa Sarai
2019-07-06 14:57 ` [PATCH v9 02/10] procfs: switch magic-link modes to be more sane Aleksa Sarai
2019-07-06 14:57 ` Aleksa Sarai [this message]
2019-07-06 14:57 ` [PATCH v9 04/10] namei: split out nd->dfd handling to dirfd_path_init Aleksa Sarai
2019-07-12 4:20 ` Al Viro
2019-07-12 12:07 ` Aleksa Sarai
2019-07-12 12:12 ` Aleksa Sarai
2019-07-06 14:57 ` [PATCH v9 05/10] namei: O_BENEATH-style path resolution flags Aleksa Sarai
2019-07-12 4:33 ` Al Viro
2019-07-12 10:57 ` Aleksa Sarai
2019-07-12 12:39 ` Al Viro
2019-07-12 12:55 ` Al Viro
2019-07-12 13:25 ` Al Viro
2019-07-12 15:00 ` Al Viro
2019-07-13 2:41 ` Al Viro
2019-07-14 3:58 ` Al Viro
2019-07-16 8:03 ` Aleksa Sarai
2019-07-14 7:00 ` Aleksa Sarai
2019-07-14 14:36 ` Al Viro
2019-07-18 3:17 ` Aleksa Sarai
2019-07-14 10:31 ` Aleksa Sarai
2019-07-06 14:57 ` [PATCH v9 06/10] namei: LOOKUP_IN_ROOT: chroot-like path resolution Aleksa Sarai
2019-07-06 14:57 ` [PATCH v9 07/10] namei: aggressively check for nd->root escape on ".." resolution Aleksa Sarai
2019-07-06 14:57 ` [PATCH v9 08/10] open: openat2(2) syscall Aleksa Sarai
2019-07-18 14:48 ` Rasmus Villemoes
2019-07-18 15:21 ` Aleksa Sarai
2019-07-18 15:10 ` Arnd Bergmann
2019-07-18 16:12 ` Aleksa Sarai
2019-07-18 21:29 ` Arnd Bergmann
2019-07-19 2:12 ` Dmitry V. Levin
2019-07-19 10:29 ` Christian Brauner
2019-07-19 1:59 ` Dmitry V. Levin
2019-07-19 2:19 ` Aleksa Sarai
2019-07-06 14:57 ` [PATCH v9 09/10] kselftest: save-and-restore errno to allow for %m formatting Aleksa Sarai
2019-07-06 14:57 ` [PATCH v9 10/10] selftests: add openat2(2) selftests Aleksa Sarai
2019-07-08 1:15 ` Michael Ellerman
2019-07-08 5:47 ` Aleksa Sarai
2019-07-12 15:11 ` [PATCH v9 00/10] namei: openat2(2) path resolution restrictions Al Viro
2019-07-12 15:32 ` Aleksa Sarai
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