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Subject[PATCHv5 6/7] perf: introduce a flag to enable close-on-exec in perf_event_open()
Date
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

Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Yann Droneaud <ydroneaud@opteya.com>
Link: http://lkml.kernel.org/r/1383168950%2d8933-1-git-send-email-ydroneaud@opteya.com
Link: http://lkml.kernel.org/r/1383170413.9171.10.camel@dworkin
Link: http://lkml.kernel.org/r/cover.1388952061.git.ydroneaud@opteya.com
---
include/uapi/linux/perf_event.h | 1 +
kernel/events/core.c | 12 +++++++++---
2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index 959d454f76a1..e244ed412745 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -725,6 +725,7 @@ 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;
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 4b743b299124..86e6a49abf8e 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -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
@@ -6995,6 +6996,7 @@ 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)
@@ -7023,7 +7025,10 @@ 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;

@@ -7145,7 +7150,8 @@ 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;
--
1.8.4.2


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