From b556db17b0e7c439bb6113b6dc7185bd0b1bbbb4 Mon Sep 17 00:00:00 2001
From: Masatake YAMATO <yamato@redhat.com>
Date: Tue, 14 May 2019 15:45:19 -0700
Subject: [PATCH] eventfd: present id to userspace via fdinfo
Finding endpoints of an IPC channel is one of essential task to
understand how a user program works. Procfs and netlink socket provide
enough hints to find endpoints for IPC channels like pipes, unix
sockets, and pseudo terminals. However, there is no simple way to find
endpoints for an eventfd file from userland. An inode number doesn't
hint. Unlike pipe, all eventfd files share the same inode object.
To provide the way to find endpoints of an eventfd file, this patch adds
"eventfd-id" field to /proc/PID/fdinfo of eventfd as identifier.
Integers managed by an IDA are used as ids.
A tool like lsof can utilize the information to print endpoints.
Link: http://lkml.kernel.org/r/20190327181823.20222-1-yamato@redhat.com
Signed-off-by: Masatake YAMATO <yamato@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
fs/eventfd.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/fs/eventfd.c b/fs/eventfd.c
index 08d3bd602f73d..ce8fa15cebe50 100644
--- a/fs/eventfd.c
+++ b/fs/eventfd.c
@@ -21,6 +21,9 @@
#include <linux/eventfd.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
+#include <linux/idr.h>
+
+DEFINE_IDA(eventfd_ida);
struct eventfd_ctx {
struct kref kref;
@@ -35,6 +38,7 @@ struct eventfd_ctx {
*/
__u64 count;
unsigned int flags;
+ int id;
};
/**
@@ -69,6 +73,8 @@ EXPORT_SYMBOL_GPL(eventfd_signal);
static void eventfd_free_ctx(struct eventfd_ctx *ctx)
{
+ if (ctx->id >= 0)
+ ida_simple_remove(&eventfd_ida, ctx->id);
kfree(ctx);
}
@@ -297,6 +303,7 @@ static void eventfd_show_fdinfo(struct seq_file *m, struct file *f)
seq_printf(m, "eventfd-count: %16llx\n",
(unsigned long long)ctx->count);
spin_unlock_irq(&ctx->wqh.lock);
+ seq_printf(m, "eventfd-id: %d\n", ctx->id);
}
#endif
@@ -400,6 +407,7 @@ static int do_eventfd(unsigned int count, int flags)
init_waitqueue_head(&ctx->wqh);
ctx->count = count;
ctx->flags = flags;
+ ctx->id = ida_simple_get(&eventfd_ida, 0, 0, GFP_KERNEL);
fd = anon_inode_getfd("[eventfd]", &eventfd_fops, ctx,
O_RDWR | (flags & EFD_SHARED_FCNTL_FLAGS));
--
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