From c3880a7b10e487e033dc6f388bda118436566f7a Mon Sep 17 00:00:00 2001 From: Junxi Qian Date: Wed, 6 May 2026 20:24:15 +0800 Subject: [PATCH] fuse: fix writeback array overflow when max_pages is one fuse_iomap_writeback_range() appends one folio pointer and one fuse_folio_desc for every dirty range that is merged into the current writeback request. The merge decision checks the byte budget against fc->max_pages and fc->max_write, but it does not check whether the folio and descriptor arrays still have another free slot. This is not sufficient for fuseblk, where the filesystem block size can be smaller than PAGE_SIZE. With writeback cache enabled and max_pages negotiated as one, contiguous sub-page dirty ranges can fit within the byte budget while spanning more than one folio. The next append can then write past the one-slot folios and descs arrays. Split the request when the number of already attached folios has reached fc->max_pages. This keeps the folio/descriptor slot accounting in sync with the send decision. Fixes: ef7e7cbb323f ("fuse: use iomap for writeback") Cc: stable@vger.kernel.org Reviewed-by: Joanne Koong Signed-off-by: Junxi Qian Link: https://patch.msgid.link/20260506122415.205340-1-qjx1298677004@gmail.com Acked-by: Miklos Szeredi Signed-off-by: Christian Brauner --- fs/fuse/file.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/fs/fuse/file.c b/fs/fuse/file.c index c59452d60b8d..f94f3dc082c6 100644 --- a/fs/fuse/file.c +++ b/fs/fuse/file.c @@ -2176,7 +2176,10 @@ static bool fuse_folios_need_send(struct fuse_conn *fc, loff_t pos, WARN_ON(!ap->num_folios); - /* Reached max pages */ + /* Reached max pages or max folio slots */ + if (ap->num_folios >= fc->max_pages) + return true; + if (DIV_ROUND_UP(bytes, PAGE_SIZE) > fc->max_pages) return true;