Messages in this thread Patch in this message | | | From | Christian Göttsche <> | Subject | [RFC PATCH] f*xattr: allow O_PATH descriptors | Date | Tue, 7 Jun 2022 17:31:39 +0200 |
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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
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