From: "Christian Göttsche" <cgzones@googlemail.com>
To: selinux@vger.kernel.org
Cc: Miklos Szeredi <mszeredi@redhat.com>,
linux-api@vger.kernel.org, linux-man@vger.kernel.org,
Alexander Viro <viro@zeniv.linux.org.uk>,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [RFC PATCH] f*xattr: allow O_PATH descriptors
Date: Tue, 7 Jun 2022 17:31:39 +0200 [thread overview]
Message-ID: <20220607153139.35588-1-cgzones@googlemail.com> (raw)
From: Miklos Szeredi <mszeredi@redhat.com>
Support file descriptors obtained via O_PATH for extended attribute
operations.
Extended attributes are for example used by SELinux for the security
context of file objects. To avoid time-of-check-time-of-use issues while
setting those contexts it is advisable to pin the file in question and
operate on a file descriptor instead of the path name. This can be
emulated in userspace via /proc/self/fd/NN [1] but requires a procfs,
which might not be mounted e.g. inside of chroots, see[2].
[1]: https://github.com/SELinuxProject/selinux/commit/7e979b56fd2cee28f647376a7233d2ac2d12ca50
[2]: https://github.com/SELinuxProject/selinux/commit/de285252a1801397306032e070793889c9466845
Original patch by Miklos Szeredi <mszeredi@redhat.com>
https://patchwork.kernel.org/project/linux-fsdevel/patch/20200505095915.11275-6-mszeredi@redhat.com/
> While this carries a minute risk of someone relying on the property of
> xattr syscalls rejecting O_PATH descriptors, it saves the trouble of
> introducing another set of syscalls.
>
> Only file->f_path and file->f_inode are accessed in these functions.
>
> Current versions return EBADF, hence easy to detect the presense of
> this feature and fall back in case it's missing.
CC: linux-api@vger.kernel.org
CC: linux-man@vger.kernel.org
Signed-off-by: Christian Göttsche <cgzones@googlemail.com>
---
fs/xattr.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/fs/xattr.c b/fs/xattr.c
index e8dd03e4561e..16360ac4eb1b 100644
--- a/fs/xattr.c
+++ b/fs/xattr.c
@@ -656,7 +656,7 @@ SYSCALL_DEFINE5(lsetxattr, const char __user *, pathname,
SYSCALL_DEFINE5(fsetxattr, int, fd, const char __user *, name,
const void __user *,value, size_t, size, int, flags)
{
- struct fd f = fdget(fd);
+ struct fd f = fdget_raw(fd);
int error = -EBADF;
if (!f.file)
@@ -768,7 +768,7 @@ SYSCALL_DEFINE4(lgetxattr, const char __user *, pathname,
SYSCALL_DEFINE4(fgetxattr, int, fd, const char __user *, name,
void __user *, value, size_t, size)
{
- struct fd f = fdget(fd);
+ struct fd f = fdget_raw(fd);
ssize_t error = -EBADF;
if (!f.file)
@@ -844,7 +844,7 @@ SYSCALL_DEFINE3(llistxattr, const char __user *, pathname, char __user *, list,
SYSCALL_DEFINE3(flistxattr, int, fd, char __user *, list, size_t, size)
{
- struct fd f = fdget(fd);
+ struct fd f = fdget_raw(fd);
ssize_t error = -EBADF;
if (!f.file)
@@ -910,7 +910,7 @@ SYSCALL_DEFINE2(lremovexattr, const char __user *, pathname,
SYSCALL_DEFINE2(fremovexattr, int, fd, const char __user *, name)
{
- struct fd f = fdget(fd);
+ struct fd f = fdget_raw(fd);
int error = -EBADF;
if (!f.file)
--
2.36.1
next reply other threads:[~2022-06-07 15:32 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-07 15:31 Christian Göttsche [this message]
2022-06-08 5:13 ` [RFC PATCH] f*xattr: allow O_PATH descriptors Amir Goldstein
2022-06-08 11:27 ` Christian Brauner
2022-06-08 12:28 ` Amir Goldstein
2022-06-08 12:48 ` Christian Brauner
2022-06-08 15:12 ` Amir Goldstein
2022-06-09 8:56 ` Christian Brauner
2022-06-18 3:18 ` Aleksa Sarai
2022-06-18 9:11 ` Amir Goldstein
2022-06-18 11:19 ` Christian Göttsche
2022-06-18 15:30 ` Amir Goldstein
2022-06-20 6:07 ` Aleksa Sarai
2022-06-20 7:45 ` Amir Goldstein
2022-06-22 2:57 ` Aleksa Sarai
2022-08-19 18:05 ` Christian Göttsche
2022-08-19 20:27 ` Amir Goldstein
2022-06-08 16:53 ` Andreas Dilger
2022-06-09 4:35 ` Amir Goldstein
2022-06-09 9:14 ` Christian Göttsche
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