This is a note to let you know that I've just added the patch titled
io_uring/kbuf: hold io_buffer_list reference over mmap
to the 6.8-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
io_uring-kbuf-hold-io_buffer_list-reference-over-mmap.patch
and it can be found in the queue-6.8 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 561e4f9451d65fc2f7eef564e0064373e3019793 Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe@xxxxxxxxx>
Date: Tue, 2 Apr 2024 16:16:03 -0600
Subject: io_uring/kbuf: hold io_buffer_list reference over mmap
From: Jens Axboe <axboe@xxxxxxxxx>
commit 561e4f9451d65fc2f7eef564e0064373e3019793 upstream.
If we look up the kbuf, ensure that it doesn't get unregistered until
after we're done with it. Since we're inside mmap, we cannot safely use
the io_uring lock. Rely on the fact that we can lookup the buffer list
under RCU now and grab a reference to it, preventing it from being
unregistered until we're done with it. The lookup returns the
io_buffer_list directly with it referenced.
Cc: stable@xxxxxxxxxxxxxxx # v6.4+
Fixes: 5cf4f52e6d8a ("io_uring: free io_buffer_list entries via RCU")
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
io_uring/io_uring.c | 11 ++++++-----
io_uring/kbuf.c | 31 +++++++++++++++++++++++++------
io_uring/kbuf.h | 4 +++-
3 files changed, 34 insertions(+), 12 deletions(-)
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -3422,14 +3422,15 @@ static void *io_uring_validate_mmap_requ
ptr = ctx->sq_sqes;
break;
case IORING_OFF_PBUF_RING: {
+ struct io_buffer_list *bl;
unsigned int bgid;
bgid = (offset & ~IORING_OFF_MMAP_MASK) >> IORING_OFF_PBUF_SHIFT;
- rcu_read_lock();
- ptr = io_pbuf_get_address(ctx, bgid);
- rcu_read_unlock();
- if (!ptr)
- return ERR_PTR(-EINVAL);
+ bl = io_pbuf_get_bl(ctx, bgid);
+ if (IS_ERR(bl))
+ return bl;
+ ptr = bl->buf_ring;
+ io_put_bl(ctx, bl);
break;
}
default:
--- a/io_uring/kbuf.c
+++ b/io_uring/kbuf.c
@@ -275,7 +275,7 @@ static int __io_remove_buffers(struct io
return i;
}
-static void io_put_bl(struct io_ring_ctx *ctx, struct io_buffer_list *bl)
+void io_put_bl(struct io_ring_ctx *ctx, struct io_buffer_list *bl)
{
if (atomic_dec_and_test(&bl->refs)) {
__io_remove_buffers(ctx, bl, -1U);
@@ -728,16 +728,35 @@ int io_register_pbuf_status(struct io_ri
return 0;
}
-void *io_pbuf_get_address(struct io_ring_ctx *ctx, unsigned long bgid)
+struct io_buffer_list *io_pbuf_get_bl(struct io_ring_ctx *ctx,
+ unsigned long bgid)
{
struct io_buffer_list *bl;
+ bool ret;
- bl = __io_buffer_get_list(ctx, bgid);
+ /*
+ * We have to be a bit careful here - we're inside mmap and cannot grab
+ * the uring_lock. This means the buffer_list could be simultaneously
+ * going away, if someone is trying to be sneaky. Look it up under rcu
+ * so we know it's not going away, and attempt to grab a reference to
+ * it. If the ref is already zero, then fail the mapping. If successful,
+ * the caller will call io_put_bl() to drop the the reference at at the
+ * end. This may then safely free the buffer_list (and drop the pages)
+ * at that point, vm_insert_pages() would've already grabbed the
+ * necessary vma references.
+ */
+ rcu_read_lock();
+ bl = xa_load(&ctx->io_bl_xa, bgid);
+ /* must be a mmap'able buffer ring and have pages */
+ ret = false;
+ if (bl && bl->is_mmap)
+ ret = atomic_inc_not_zero(&bl->refs);
+ rcu_read_unlock();
- if (!bl || !bl->is_mmap)
- return NULL;
+ if (ret)
+ return bl;
- return bl->buf_ring;
+ return ERR_PTR(-EINVAL);
}
/*
--- a/io_uring/kbuf.h
+++ b/io_uring/kbuf.h
@@ -61,7 +61,9 @@ unsigned int __io_put_kbuf(struct io_kio
bool io_kbuf_recycle_legacy(struct io_kiocb *req, unsigned issue_flags);
-void *io_pbuf_get_address(struct io_ring_ctx *ctx, unsigned long bgid);
+void io_put_bl(struct io_ring_ctx *ctx, struct io_buffer_list *bl);
+struct io_buffer_list *io_pbuf_get_bl(struct io_ring_ctx *ctx,
+ unsigned long bgid);
static inline bool io_kbuf_recycle_ring(struct io_kiocb *req)
{
Patches currently in stable-queue which might be from axboe@xxxxxxxxx are
queue-6.8/io_uring-rw-don-t-allow-multishot-reads-without-nowait-support.patch
queue-6.8/io_uring-use-private-workqueue-for-exit-work.patch
queue-6.8/io_uring-kbuf-protect-io_buffer_list-teardown-with-a-reference.patch
queue-6.8/io_uring-kbuf-hold-io_buffer_list-reference-over-mmap.patch
queue-6.8/io_uring-kbuf-get-rid-of-lower-bgid-lists.patch
queue-6.8/io_uring-kbuf-get-rid-of-bl-is_ready.patch
