Re: Stack corruption in bch2_nocow_write

[Kent Overstreet]

On Fri, Dec 29, 2023 at 07:43:13PM +0800, Daniel J Blueman wrote:
> Hi Kent et al,
> 
> On Linux 6.7-rc7 from bcachefs master SHA f3608cbdfd built with UBSAN
> [1], with a crafted workload [2] I'm able to trigger stack corruption
> in bch2_nocow_write [3].
> 
> Let me know if you can't reproduce it and I'll check reproducibility
> on another platform, and let me know for any patch testing.

this should be fixed in the testing branch:

commit ab35f724070ccdaa31f6376a1890473e7d031ed0
Author: Kent Overstreet <kent.overstreet@xxxxxxxxx>
Date:   Fri Dec 29 13:54:00 2023 -0500

    bcachefs: fix nocow write path when writing to multiple extents
    
    Signed-off-by: Kent Overstreet <kent.overstreet@xxxxxxxxx>

diff --git a/fs/bcachefs/io_write.c b/fs/bcachefs/io_write.c
index c5961bac19f0..7c5963cd0b85 100644
--- a/fs/bcachefs/io_write.c
+++ b/fs/bcachefs/io_write.c
@@ -1316,6 +1316,7 @@ static void bch2_nocow_write(struct bch_write_op *op)
 		closure_get(&op->cl);
 		bch2_submit_wbio_replicas(to_wbio(bio), c, BCH_DATA_user,
 					  op->insert_keys.top, true);
+		nr_buckets = 0;
 
 		bch2_keylist_push(&op->insert_keys);
 		if (op->flags & BCH_WRITE_DONE)