Commit a21b0b35 authored Jan 05, 2014 by Yann Droneaud Committed by Ingo Molnar Jan 12, 2014

perf: Introduce a flag to enable close-on-exec in perf_event_open()

Unlike recent modern userspace API such as:

  epoll_create1 (EPOLL_CLOEXEC), eventfd (EFD_CLOEXEC),
  fanotify_init (FAN_CLOEXEC), inotify_init1 (IN_CLOEXEC),
  signalfd (SFD_CLOEXEC), timerfd_create (TFD_CLOEXEC),
  or the venerable general purpose open (O_CLOEXEC),

perf_event_open() syscall lack a flag to atomically set FD_CLOEXEC
(eg. close-on-exec) flag on file descriptor it returns to userspace.

The present patch adds a PERF_FLAG_FD_CLOEXEC flag to allow
perf_event_open() syscall to atomically set close-on-exec.

Having this flag will enable userspace to remove the file descriptor
from the list of file descriptors being inherited across exec,
without the need to call fcntl(fd, F_SETFD, FD_CLOEXEC) and the
associated race condition between the current thread and another
thread calling fork(2) then execve(2).

Links:

 - Secure File Descriptor Handling (Ulrich Drepper, 2008)
   http://udrepper.livejournal.com/20407.html

 - Excuse me son, but your code is leaking !!! (Dan Walsh, March 2012)
   http://danwalsh.livejournal.com/53603.html

 - Notes in DMA buffer sharing: leak and security hole
   http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/dma-buf-sharing.txt?id=v3.13-rc3#n428



Signed-off-by: Yann Droneaud <ydroneaud@opteya.com>
Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/8c03f54e1598b1727c19706f3af03f98685d9fe6.1388952061.git.ydroneaud@opteya.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent f228c5b8

include/uapi/linux/perf_event.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -724,6 +724,7 @@ enum perf_callchain_context {
		#define PERF_FLAG_FD_NO_GROUP (1U << 0)
		#define PERF_FLAG_FD_OUTPUT (1U << 1)
		#define PERF_FLAG_PID_CGROUP (1U << 2) /* pid=cgroup id, per-cpu mode only */
		#define PERF_FLAG_FD_CLOEXEC (1U << 3) /* O_CLOEXEC */

		union perf_mem_data_src {
		__u64 val;

kernel/events/core.c

+9 −3

Original line number	Diff line number	Diff line
		@@ -119,7 +119,8 @@ static int cpu_function_call(int cpu, int (func) (void info), void *info)

		#define PERF_FLAG_ALL (PERF_FLAG_FD_NO_GROUP \|\
		PERF_FLAG_FD_OUTPUT \|\
		PERF_FLAG_PID_CGROUP)
		PERF_FLAG_PID_CGROUP \|\
		PERF_FLAG_FD_CLOEXEC)

		/*
		* branch priv levels that need permission checks
		@@ -6982,6 +6983,7 @@ SYSCALL_DEFINE5(perf_event_open,
		int event_fd;
		int move_group = 0;
		int err;
		int f_flags = O_RDWR;

		/* for future expandability... */
		if (flags & ~PERF_FLAG_ALL)
		@@ -7010,7 +7012,10 @@ SYSCALL_DEFINE5(perf_event_open,
		if ((flags & PERF_FLAG_PID_CGROUP) && (pid == -1 \|\| cpu == -1))
		return -EINVAL;

		event_fd = get_unused_fd();
		if (flags & PERF_FLAG_FD_CLOEXEC)
		f_flags \|= O_CLOEXEC;

		event_fd = get_unused_fd_flags(f_flags);
		if (event_fd < 0)
		return event_fd;

		@@ -7132,7 +7137,8 @@ SYSCALL_DEFINE5(perf_event_open,
		goto err_context;
		}

		event_file = anon_inode_getfile("[perf_event]", &perf_fops, event, O_RDWR);
		event_file = anon_inode_getfile("[perf_event]", &perf_fops, event,
		f_flags);
		if (IS_ERR(event_file)) {
		err = PTR_ERR(event_file);
		goto err_context;