Received: by 2002:a25:8b91:0:0:0:0:0 with SMTP id j17csp3771516ybl; Fri, 20 Dec 2019 15:29:31 -0800 (PST) X-Google-Smtp-Source: APXvYqyEVoxMGPRG2MLrseIz8QId3Kxd5FPiz3PfCx9U06GVhKjez4R1UbeVNCLqoLl7QVdt5abO X-Received: by 2002:a05:6830:4a4:: with SMTP id l4mr17907351otd.91.1576884571038; Fri, 20 Dec 2019 15:29:31 -0800 (PST) ARC-Seal: i=1; a=rsa-sha256; t=1576884571; cv=none; d=google.com; s=arc-20160816; b=gaBKL12kufokdYnmTPcixE5W2SfPpxA8fEBauCE/WP4IPXiOvFVvzIOrt2SswmOIY1 88x+0roDb1WK5uPXxUMkqB1dlFk/wVsmN1GRyx4Sk6fmPF5qjWeXJIZAHJFTVTqntbC6 XmLDGH5oQD4W81qxn+4r0XCffpNf73KyHsOTBYirz3FEBYhFRU5rDJxOEdV5XMB+illr Z5ma84OabbGZ1fjKIQmzOxR6muf2lPOmU4tvOnYczvC2qI9BaAkrE+qICvLf2XusCvSC jWAcBTyYbpkR/zUqRtvy0/5xs9x55p0LfVUIy3kvTVzwfOJiR6cn/9pSqQ+/eeVFPYhB 6pFw== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:sender:user-agent:content-disposition :mime-version:message-id:subject:cc:to:from:date:dkim-signature; bh=kxHJTJjVCyhCiL727OkEZRZ43OQtsu2M3mcaBbYHQdc=; b=yMkf8wk9i2CwQYzCa15Irq5XUCyi23rufMWncwhBhScj9x1Vodv/NbWjViNk7/KHwu inA98hptr4AeoPpiRwrJTuwHJorztKWKtQXh9l62iCSHH7lLGcWhmRXQHBN2hH9fKVpA a6iUXTTShaKap8NivAxpcVaFDjnHYbZGwx1IjIGKxdXgCCENam7om3sEnMWx4xq1b0yU aIflf9b6/AqADYXaVuwIymc+mtt8SIU7CmzppUo0SS2Q0AfrNB1tE5O93qEQWrNMnqXU yb7lOUkaUS6k0/cpDHmhNzq2QgrLZMZCvswYGL1UfAjqDygUAqLIKCh1xxu4E3maYj4p 3kXA== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@sargun.me header.s=google header.b=UChnFr9Z; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Return-Path: Received: from vger.kernel.org (vger.kernel.org. [209.132.180.67]) by mx.google.com with ESMTP id m17si4326415otr.17.2019.12.20.15.29.19; Fri, 20 Dec 2019 15:29:31 -0800 (PST) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; dkim=pass header.i=@sargun.me header.s=google header.b=UChnFr9Z; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726786AbfLTX2R (ORCPT + 99 others); Fri, 20 Dec 2019 18:28:17 -0500 Received: from mail-io1-f68.google.com ([209.85.166.68]:46899 "EHLO mail-io1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726741AbfLTX2R (ORCPT ); Fri, 20 Dec 2019 18:28:17 -0500 Received: by mail-io1-f68.google.com with SMTP id t26so11026625ioi.13 for ; Fri, 20 Dec 2019 15:28:16 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sargun.me; s=google; h=date:from:to:cc:subject:message-id:mime-version:content-disposition :user-agent; bh=kxHJTJjVCyhCiL727OkEZRZ43OQtsu2M3mcaBbYHQdc=; b=UChnFr9ZV27wTdAuMUPmfv43PiMUhXrdziHHrL+VNiSNSjzKdwMDrqxPXXuFHUP8Eq 64nUoCssNpp3PFlSwO39jWdyY5O/jiMF8ORIZw3rRgKOYQNGAtEyCQpt82s+sHN2c/ue ai5qPz5cDl/cOLJ24XKPf6Pm1n8tdDPbY+xgc= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:mime-version :content-disposition:user-agent; bh=kxHJTJjVCyhCiL727OkEZRZ43OQtsu2M3mcaBbYHQdc=; b=ghkvqrgmhyUDra+5evpmRyto0q/o88LsDLyfYa/61xF9Rown28p6smLQSIFWGDQ/6F Zz7ws4+OVLsxESRFyIImV43dbKXpIEHNKqhYwDjryWb8hMldGDF5kpKFzA5/kzS1UoN6 kr9NhlqaebeEo0NSusUiS3QAvDfYv32kRyEq32IZKgirrRJPHcOKZCvj8RjAu2hM37ys yU6ORF6xOxsziQ6cGQlAGMj8Ge1EJ1hxIzjkOK6OfafhN57QEx+6g6173LdqURtjPKX6 m3AcVy97I15GVeccvYpGTNGOAQDMpgz57wABBi4ZbnNMdat+SAuiBB2lm/m9em+zxrmD 4AqA== X-Gm-Message-State: APjAAAUcPgdAm55SrM72OjgjQwxzzhBL1xyhFv4tEJel/lpyYtdolOC9 dnMI0eLzKesfatkwGFDzTxnRoKoYniUHVQ== X-Received: by 2002:a6b:b297:: with SMTP id b145mr12410260iof.19.1576884495205; Fri, 20 Dec 2019 15:28:15 -0800 (PST) Received: from ircssh-2.c.rugged-nimbus-611.internal (80.60.198.104.bc.googleusercontent.com. [104.198.60.80]) by smtp.gmail.com with ESMTPSA id s10sm3914224ioc.4.2019.12.20.15.28.14 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 20 Dec 2019 15:28:14 -0800 (PST) Date: Fri, 20 Dec 2019 23:28:13 +0000 From: Sargun Dhillon To: linux-kernel@vger.kernel.org, containers@lists.linux-foundation.org, linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org Cc: tycho@tycho.ws, jannh@google.com, cyphar@cyphar.com, christian.brauner@ubuntu.com, oleg@redhat.com, luto@amacapital.net, viro@zeniv.linux.org.uk, gpascutto@mozilla.com, ealvarez@mozilla.com, fweimer@redhat.com, jld@mozilla.com, arnd@arndb.de Subject: [PATCH v5 2/3] pid: Introduce pidfd_getfd syscall Message-ID: <20191220232810.GA20233@ircssh-2.c.rugged-nimbus-611.internal> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This syscall allows for the retrieval of file descriptors from other processes, based on their pidfd. This is possible using ptrace, and injection of parasitic code along with using SCM_RIGHTS to move file descriptors between a tracee and a tracer. Unfortunately, ptrace comes with a high cost of requiring the process to be stopped, and breaks debuggers. This does not require stopping the process under manipulation. One reason to use this is to allow sandboxers to take actions on file descriptors on the behalf of another process. For example, this can be combined with seccomp-bpf's user notification to do on-demand fd extraction and take privileged actions. For example, it can be used to bind a socket to a privileged port. /* prototype */ /* * pidfd_getfd_options is an extensible struct which can have options * added to it. If options is NULL, size, and it will be ignored be * ignored, otherwise, size should be set to sizeof(*options). If * option is newer than the current kernel version, E2BIG will be * returned. */ struct pidfd_getfd_options {}; long pidfd_getfd(int pidfd, int fd, unsigned int flags, struct pidfd_getfd_options *options, size_t size); /* testing */ Ran self-test suite on x86_64 Signed-off-by: Sargun Dhillon --- MAINTAINERS | 1 + arch/alpha/kernel/syscalls/syscall.tbl | 1 + arch/arm/tools/syscall.tbl | 1 + arch/arm64/include/asm/unistd.h | 2 +- arch/arm64/include/asm/unistd32.h | 2 + arch/ia64/kernel/syscalls/syscall.tbl | 1 + arch/m68k/kernel/syscalls/syscall.tbl | 1 + arch/microblaze/kernel/syscalls/syscall.tbl | 1 + arch/mips/kernel/syscalls/syscall_n32.tbl | 1 + arch/mips/kernel/syscalls/syscall_n64.tbl | 1 + arch/mips/kernel/syscalls/syscall_o32.tbl | 1 + arch/parisc/kernel/syscalls/syscall.tbl | 1 + arch/powerpc/kernel/syscalls/syscall.tbl | 1 + arch/s390/kernel/syscalls/syscall.tbl | 1 + arch/sh/kernel/syscalls/syscall.tbl | 1 + arch/sparc/kernel/syscalls/syscall.tbl | 1 + arch/x86/entry/syscalls/syscall_32.tbl | 1 + arch/x86/entry/syscalls/syscall_64.tbl | 1 + arch/xtensa/kernel/syscalls/syscall.tbl | 1 + include/linux/syscalls.h | 4 + include/uapi/asm-generic/unistd.h | 3 +- include/uapi/linux/pidfd.h | 10 ++ kernel/pid.c | 115 ++++++++++++++++++++ 23 files changed, 151 insertions(+), 2 deletions(-) create mode 100644 include/uapi/linux/pidfd.h diff --git a/MAINTAINERS b/MAINTAINERS index cc0a4a8ae06a..bc370ff59dbf 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -13014,6 +13014,7 @@ M: Christian Brauner L: linux-kernel@vger.kernel.org S: Maintained T: git git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux.git +F: include/uapi/linux/pidfd.h F: samples/pidfd/ F: tools/testing/selftests/pidfd/ F: tools/testing/selftests/clone3/ diff --git a/arch/alpha/kernel/syscalls/syscall.tbl b/arch/alpha/kernel/syscalls/syscall.tbl index 8e13b0b2928d..d1cac0d657b7 100644 --- a/arch/alpha/kernel/syscalls/syscall.tbl +++ b/arch/alpha/kernel/syscalls/syscall.tbl @@ -475,3 +475,4 @@ 543 common fspick sys_fspick 544 common pidfd_open sys_pidfd_open # 545 reserved for clone3 +548 common pidfd_getfd sys_pidfd diff --git a/arch/arm/tools/syscall.tbl b/arch/arm/tools/syscall.tbl index 6da7dc4d79cc..ba045e2f3a60 100644 --- a/arch/arm/tools/syscall.tbl +++ b/arch/arm/tools/syscall.tbl @@ -449,3 +449,4 @@ 433 common fspick sys_fspick 434 common pidfd_open sys_pidfd_open 435 common clone3 sys_clone3 +438 common pidfd_getfd sys_pidfd_getfd diff --git a/arch/arm64/include/asm/unistd.h b/arch/arm64/include/asm/unistd.h index 2629a68b8724..b722e47377a5 100644 --- a/arch/arm64/include/asm/unistd.h +++ b/arch/arm64/include/asm/unistd.h @@ -38,7 +38,7 @@ #define __ARM_NR_compat_set_tls (__ARM_NR_COMPAT_BASE + 5) #define __ARM_NR_COMPAT_END (__ARM_NR_COMPAT_BASE + 0x800) -#define __NR_compat_syscalls 436 +#define __NR_compat_syscalls 439 #endif #define __ARCH_WANT_SYS_CLONE diff --git a/arch/arm64/include/asm/unistd32.h b/arch/arm64/include/asm/unistd32.h index 94ab29cf4f00..a8da97a2de41 100644 --- a/arch/arm64/include/asm/unistd32.h +++ b/arch/arm64/include/asm/unistd32.h @@ -879,6 +879,8 @@ __SYSCALL(__NR_fspick, sys_fspick) __SYSCALL(__NR_pidfd_open, sys_pidfd_open) #define __NR_clone3 435 __SYSCALL(__NR_clone3, sys_clone3) +#define __NR_pidfd_getfd 438 +__SYSCALL(__NR_pidfd_getfd, sys_pidfd_getfd) /* * Please add new compat syscalls above this comment and update diff --git a/arch/ia64/kernel/syscalls/syscall.tbl b/arch/ia64/kernel/syscalls/syscall.tbl index 36d5faf4c86c..2b11adfc860c 100644 --- a/arch/ia64/kernel/syscalls/syscall.tbl +++ b/arch/ia64/kernel/syscalls/syscall.tbl @@ -356,3 +356,4 @@ 433 common fspick sys_fspick 434 common pidfd_open sys_pidfd_open # 435 reserved for clone3 +438 common pidfd_getfd sys_pidfd_getfd diff --git a/arch/m68k/kernel/syscalls/syscall.tbl b/arch/m68k/kernel/syscalls/syscall.tbl index a88a285a0e5f..44e879e98459 100644 --- a/arch/m68k/kernel/syscalls/syscall.tbl +++ b/arch/m68k/kernel/syscalls/syscall.tbl @@ -435,3 +435,4 @@ 433 common fspick sys_fspick 434 common pidfd_open sys_pidfd_open # 435 reserved for clone3 +438 common pidfd_getfd sys_pidfd_getfd diff --git a/arch/microblaze/kernel/syscalls/syscall.tbl b/arch/microblaze/kernel/syscalls/syscall.tbl index 09b0cd7dab0a..7afa00125cc4 100644 --- a/arch/microblaze/kernel/syscalls/syscall.tbl +++ b/arch/microblaze/kernel/syscalls/syscall.tbl @@ -441,3 +441,4 @@ 433 common fspick sys_fspick 434 common pidfd_open sys_pidfd_open 435 common clone3 sys_clone3 +438 common pidfd_getfd sys_pidfd_getfd diff --git a/arch/mips/kernel/syscalls/syscall_n32.tbl b/arch/mips/kernel/syscalls/syscall_n32.tbl index e7c5ab38e403..856d5ba34461 100644 --- a/arch/mips/kernel/syscalls/syscall_n32.tbl +++ b/arch/mips/kernel/syscalls/syscall_n32.tbl @@ -374,3 +374,4 @@ 433 n32 fspick sys_fspick 434 n32 pidfd_open sys_pidfd_open 435 n32 clone3 __sys_clone3 +438 n32 pidfd_getfd sys_pidfd_getfd diff --git a/arch/mips/kernel/syscalls/syscall_n64.tbl b/arch/mips/kernel/syscalls/syscall_n64.tbl index 13cd66581f3b..2db6075352f3 100644 --- a/arch/mips/kernel/syscalls/syscall_n64.tbl +++ b/arch/mips/kernel/syscalls/syscall_n64.tbl @@ -350,3 +350,4 @@ 433 n64 fspick sys_fspick 434 n64 pidfd_open sys_pidfd_open 435 n64 clone3 __sys_clone3 +438 n64 pidfd_getfd sys_pidfd_getfd diff --git a/arch/mips/kernel/syscalls/syscall_o32.tbl b/arch/mips/kernel/syscalls/syscall_o32.tbl index 353539ea4140..e9f9d4a9b105 100644 --- a/arch/mips/kernel/syscalls/syscall_o32.tbl +++ b/arch/mips/kernel/syscalls/syscall_o32.tbl @@ -423,3 +423,4 @@ 433 o32 fspick sys_fspick 434 o32 pidfd_open sys_pidfd_open 435 o32 clone3 __sys_clone3 +438 o32 pidfd_getfd sys_pidfd_getfd diff --git a/arch/parisc/kernel/syscalls/syscall.tbl b/arch/parisc/kernel/syscalls/syscall.tbl index 285ff516150c..c58c7eb144ca 100644 --- a/arch/parisc/kernel/syscalls/syscall.tbl +++ b/arch/parisc/kernel/syscalls/syscall.tbl @@ -433,3 +433,4 @@ 433 common fspick sys_fspick 434 common pidfd_open sys_pidfd_open 435 common clone3 sys_clone3_wrapper +438 common pidfd_getfd sys_pidfd_getfd diff --git a/arch/powerpc/kernel/syscalls/syscall.tbl b/arch/powerpc/kernel/syscalls/syscall.tbl index 43f736ed47f2..707609bfe3ea 100644 --- a/arch/powerpc/kernel/syscalls/syscall.tbl +++ b/arch/powerpc/kernel/syscalls/syscall.tbl @@ -517,3 +517,4 @@ 433 common fspick sys_fspick 434 common pidfd_open sys_pidfd_open 435 nospu clone3 ppc_clone3 +438 common pidfd_getfd sys_pidfd_getfd diff --git a/arch/s390/kernel/syscalls/syscall.tbl b/arch/s390/kernel/syscalls/syscall.tbl index 3054e9c035a3..185cd624face 100644 --- a/arch/s390/kernel/syscalls/syscall.tbl +++ b/arch/s390/kernel/syscalls/syscall.tbl @@ -438,3 +438,4 @@ 433 common fspick sys_fspick sys_fspick 434 common pidfd_open sys_pidfd_open sys_pidfd_open 435 common clone3 sys_clone3 sys_clone3 +438 common pidfd_getfd sys_pidfd_getfd sys_pidfd_getfd diff --git a/arch/sh/kernel/syscalls/syscall.tbl b/arch/sh/kernel/syscalls/syscall.tbl index b5ed26c4c005..88f90895aad8 100644 --- a/arch/sh/kernel/syscalls/syscall.tbl +++ b/arch/sh/kernel/syscalls/syscall.tbl @@ -438,3 +438,4 @@ 433 common fspick sys_fspick 434 common pidfd_open sys_pidfd_open # 435 reserved for clone3 +438 common pidfd_getfd sys_pidfd_getfd diff --git a/arch/sparc/kernel/syscalls/syscall.tbl b/arch/sparc/kernel/syscalls/syscall.tbl index 8c8cc7537fb2..218df6a2326e 100644 --- a/arch/sparc/kernel/syscalls/syscall.tbl +++ b/arch/sparc/kernel/syscalls/syscall.tbl @@ -481,3 +481,4 @@ 433 common fspick sys_fspick 434 common pidfd_open sys_pidfd_open # 435 reserved for clone3 +438 common pidfd_getfd sys_pidfd_getfd diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl index 15908eb9b17e..9c3101b65e0f 100644 --- a/arch/x86/entry/syscalls/syscall_32.tbl +++ b/arch/x86/entry/syscalls/syscall_32.tbl @@ -440,3 +440,4 @@ 433 i386 fspick sys_fspick __ia32_sys_fspick 434 i386 pidfd_open sys_pidfd_open __ia32_sys_pidfd_open 435 i386 clone3 sys_clone3 __ia32_sys_clone3 +438 i386 pidfd_getfd sys_pidfd_getfd __ia32_sys_pidfd_getfd diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl index c29976eca4a8..cef85db75a62 100644 --- a/arch/x86/entry/syscalls/syscall_64.tbl +++ b/arch/x86/entry/syscalls/syscall_64.tbl @@ -357,6 +357,7 @@ 433 common fspick __x64_sys_fspick 434 common pidfd_open __x64_sys_pidfd_open 435 common clone3 __x64_sys_clone3/ptregs +438 common pidfd_getfd __x64_sys_pidfd_getfd # # x32-specific system call numbers start at 512 to avoid cache impact diff --git a/arch/xtensa/kernel/syscalls/syscall.tbl b/arch/xtensa/kernel/syscalls/syscall.tbl index 25f4de729a6d..ae15183def12 100644 --- a/arch/xtensa/kernel/syscalls/syscall.tbl +++ b/arch/xtensa/kernel/syscalls/syscall.tbl @@ -406,3 +406,4 @@ 433 common fspick sys_fspick 434 common pidfd_open sys_pidfd_open 435 common clone3 sys_clone3 +438 common pidfd_getfd sys_pidfd_getfd diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h index 2960dedcfde8..62fe706329d1 100644 --- a/include/linux/syscalls.h +++ b/include/linux/syscalls.h @@ -69,6 +69,7 @@ struct rseq; union bpf_attr; struct io_uring_params; struct clone_args; +struct pidfd_getfd_options; #include #include @@ -1000,6 +1001,9 @@ asmlinkage long sys_fspick(int dfd, const char __user *path, unsigned int flags) asmlinkage long sys_pidfd_send_signal(int pidfd, int sig, siginfo_t __user *info, unsigned int flags); +asmlinkage long sys_pidfd_getfd(int pidfd, int fd, + struct pidfd_getfd_options __user *options, + size_t, usize); /* * Architecture-specific system calls diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h index 1fc8faa6e973..f358488366f6 100644 --- a/include/uapi/asm-generic/unistd.h +++ b/include/uapi/asm-generic/unistd.h @@ -850,9 +850,10 @@ __SYSCALL(__NR_pidfd_open, sys_pidfd_open) #define __NR_clone3 435 __SYSCALL(__NR_clone3, sys_clone3) #endif +#define __NR_pidfd_getfd 438 #undef __NR_syscalls -#define __NR_syscalls 436 +#define __NR_syscalls 439 /* * 32 bit systems traditionally used different diff --git a/include/uapi/linux/pidfd.h b/include/uapi/linux/pidfd.h new file mode 100644 index 000000000000..0a3fc922661d --- /dev/null +++ b/include/uapi/linux/pidfd.h @@ -0,0 +1,10 @@ +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */ +#ifndef _UAPI_LINUX_PIDFD_H +#define _UAPI_LINUX_PIDFD_H + +struct pidfd_getfd_options {}; + +#define PIDFD_GETFD_OPTIONS_SIZE_VER0 0 +#define PIDFD_GETFD_OPTIONS_SIZE_LATEST PIDFD_GETFD_OPTIONS_SIZE_VER0 + +#endif /* _UAPI_LINUX_PIDFD_H */ diff --git a/kernel/pid.c b/kernel/pid.c index 2278e249141d..2a9cb4be383f 100644 --- a/kernel/pid.c +++ b/kernel/pid.c @@ -42,6 +42,7 @@ #include #include #include +#include struct pid init_struct_pid = { .count = REFCOUNT_INIT(1), @@ -578,3 +579,117 @@ void __init pid_idr_init(void) init_pid_ns.pid_cachep = KMEM_CACHE(pid, SLAB_HWCACHE_ALIGN | SLAB_PANIC | SLAB_ACCOUNT); } + +static struct file *__pidfd_getfd_fget_task(struct task_struct *task, u32 fd) +{ + struct file *file; + int ret; + + ret = mutex_lock_killable(&task->signal->cred_guard_mutex); + if (ret) + return ERR_PTR(ret); + + if (!ptrace_may_access(task, PTRACE_MODE_ATTACH_REALCREDS)) { + file = ERR_PTR(-EPERM); + goto out; + } + + file = fget_task(task, fd); + if (!file) + file = ERR_PTR(-EBADF); + +out: + mutex_unlock(&task->signal->cred_guard_mutex); + return file; +} + +static long pidfd_getfd(struct pid *pid, u32 fd) +{ + struct task_struct *task; + struct file *file; + int ret, retfd; + + task = get_pid_task(pid, PIDTYPE_PID); + if (!task) + return -ESRCH; + + file = __pidfd_getfd_fget_task(task, fd); + put_task_struct(task); + if (IS_ERR(file)) + return PTR_ERR(file); + + retfd = get_unused_fd_flags(O_CLOEXEC); + if (retfd < 0) { + ret = retfd; + goto out; + } + + /* + * security_file_receive must come last since it may have side effects + * and cannot be reversed. + */ + ret = security_file_receive(file); + if (ret) + goto out_put_fd; + + fd_install(retfd, file); + return retfd; + +out_put_fd: + put_unused_fd(retfd); +out: + fput(file); + return ret; +} + +/** + * sys_pidfd_getfd() - Get a file descriptor from another process + * + * @pidfd: file descriptor of the process + * @fd: the file descriptor number to get + * @options: options on how to get the fd + * @usize: the size of options + * + * This syscall requires that the process has the ability to ptrace the + * process represented by the pidfd. It will return a duplicated version + * of the file descriptor on success. The process who which is having + * its file descriptor taken is otherwise unaffected. If options is NULL + * it is ignored along with usize. + * + * Return: On success, a file descriptor with cloexec is returned. + * On error, a negative errno number will be returned. + */ +SYSCALL_DEFINE4(pidfd_getfd, int, pidfd, int, fd, + struct pidfd_getfd_options __user *, options, size_t, usize) +{ + struct pid *pid; + struct fd f; + int ret; + + BUILD_BUG_ON(sizeof(struct pidfd_getfd_options) != PIDFD_GETFD_OPTIONS_SIZE_LATEST); + + /* + * options is currently unused, verify it's unset or if it is set, + * ensure that size is 0. + * + * In the future, this will need to adopt copy_struct_from_user. + */ + if (options && usize > PIDFD_GETFD_OPTIONS_SIZE_VER0) + return -E2BIG; + + f = fdget(pidfd); + if (!f.file) + return -EBADF; + + pid = pidfd_pid(f.file); + if (IS_ERR(pid)) { + ret = PTR_ERR(pid); + goto out; + } + + ret = pidfd_getfd(pid, fd); + +out: + fdput(f); + return ret; +} -- 2.20.1