[PATCH 5.10 30/37] io_uring: disable polling pollfree files

Greg Kroah-Hartman
2022-09-02T13:00:19Z

From: Pavel Begunkov <asml.silence@gmail.com>

Older kernels lack io_uring POLLFREE handling. As only affected files
are signalfd and android binder the safest option would be to disable
polling those files via io_uring and hope there are no users.

Fixes: 221c5eb233823 ("io_uring: add support for IORING_OP_POLL")
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/android/binder.c | 1 +
fs/io_uring.c | 5 +++++
fs/signalfd.c | 1 +
include/linux/fs.h | 1 +
4 files changed, 8 insertions(+)

--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -6069,6 +6069,7 @@ const struct file_operations binder_fops
.open = binder_open,
.flush = binder_flush,
.release = binder_release,
+ .may_pollfree = true,
};

static int __init init_binder_device(const char *name)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -5198,6 +5198,11 @@ static __poll_t __io_arm_poll_handler(st
struct io_ring_ctx *ctx = req->ctx;
bool cancel = false;

+ if (req->file->f_op->may_pollfree) {
+ spin_lock_irq(&ctx->completion_lock);
+ return -EOPNOTSUPP;
+ }
+
INIT_HLIST_NODE(&req->hash_node);
io_init_poll_iocb(poll, mask, wake_func);
poll->file = req->file;
--- a/fs/signalfd.c
+++ b/fs/signalfd.c
@@ -248,6 +248,7 @@ static const struct file_operations sign
.poll = signalfd_poll,
.read = signalfd_read,
.llseek = noop_llseek,
+ .may_pollfree = true,
};

static int do_signalfd4(int ufd, sigset_t *mask, int flags)
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1859,6 +1859,7 @@ struct file_operations {
struct file *file_out, loff_t pos_out,
loff_t len, unsigned int remap_flags);
int (*fadvise)(struct file *, loff_t, loff_t, int);
+ bool may_pollfree;
} __randomize_layout;

struct inode_operations {