From: Miklos Szeredi <mszeredi@xxxxxxxxxx> 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@xxxxxxxxxx> https://patchwork.kernel.org/project/linux-fsdevel/patch/20200505095915.11275-6-mszeredi@xxxxxxxxxx/ > 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@xxxxxxxxxxxxxxx CC: linux-man@xxxxxxxxxxxxxxx Signed-off-by: Christian Göttsche <cgzones@xxxxxxxxxxxxxx> --- 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
