[pve-devel] [[PATCH kernel]] fix 5683: netfs: reset subreq iov iter before tail clean

[Christian Ebner]

Fixes rare read corruption issues using the in kernel ceph client.

On incomplete read requests, the clean tail flag should make sure to
zero fill the remaining bytes for the subrequest.
If the iov iterator is not at the correct position, this can however
zero fill downloaded data, corrupting the read content.

Link to issue:
https://bugzilla.proxmox.com/show_bug.cgi?id=5683

Link to upstream issue:
https://bugzilla.kernel.org/show_bug.cgi?id=219237

Signed-off-by: Christian Ebner <c.ebner at proxmox.com>
---
This fixes the read corruption issue with my local reproducer.

Providing a patched kernel to users affected by the issue for testing
would be probably the best way to verify the fix.

Also, I reached out once again to the kernel developers asking if
this fix is a valid approach, hoping this can be included in current
stable (as the patch does fix the issue also when applied on 6.11.1).

 ...et-subreq-iov-iter-before-tail-clean.patch | 31 +++++++++++++++++++
 1 file changed, 31 insertions(+)
 create mode 100644 patches/kernel/0021-netfs-reset-subreq-iov-iter-before-tail-clean.patch

diff --git a/patches/kernel/0021-netfs-reset-subreq-iov-iter-before-tail-clean.patch b/patches/kernel/0021-netfs-reset-subreq-iov-iter-before-tail-clean.patch
new file mode 100644
index 0000000..a87e722
--- /dev/null
+++ b/patches/kernel/0021-netfs-reset-subreq-iov-iter-before-tail-clean.patch
@@ -0,0 +1,31 @@
+From cd27abf0c555f39b12c05f9f6a8cb59ff25dfe45 Mon Sep 17 00:00:00 2001
+From: Christian Ebner <c.ebner at proxmox.com>
+Date: Wed, 2 Oct 2024 15:24:31 +0200
+Subject: [PATCH] netfs: reset subreq iov iter before tail clean
+
+Make sure the iter is at the correct location when cleaning up tail
+bytes for incomplete read subrequests.
+
+Fixes: 92b6cc5d ("netfs: Add iov_iters to (sub)requests to describe various buffers")
+Closes: https://bugzilla.kernel.org/show_bug.cgi?id=219237
+
+Signed-off-by: Christian Ebner <c.ebner at proxmox.com>
+---
+ fs/netfs/io.c | 1 +
+ 1 file changed, 1 insertion(+)
+
+diff --git a/fs/netfs/io.c b/fs/netfs/io.c
+index d6ada4eba744..500119285346 100644
+--- a/fs/netfs/io.c
++++ b/fs/netfs/io.c
+@@ -528,6 +528,7 @@ void netfs_subreq_terminated(struct netfs_io_subrequest *subreq,
+ 
+ incomplete:
+ 	if (test_bit(NETFS_SREQ_CLEAR_TAIL, &subreq->flags)) {
++		netfs_reset_subreq_iter(rreq, subreq);
+ 		netfs_clear_unread(subreq);
+ 		subreq->transferred = subreq->len;
+ 		goto complete;
+-- 
+2.39.5
+
-- 
2.39.5