From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 69B603BB115; Sat, 17 Oct 2026 16:48:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792255728; cv=none; b=ltNQGhPmSYM+blDrug0dIS9YqjXatqT0lz195m7Tsf89LvtN6YI7QzamoxUPoVLQgTx8HrtkLQRydrs4efXzFGYlqGIYsB4LByEw5K0ACOz0fSQtoQjvXbKhCYmA12YCt/jKXi8EcUwRfpTPoE52ilsPjYk+zBs0Y5Hxj02/Lrg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792255728; c=relaxed/simple; bh=Ge3C7unONvp4HjPN9cjmiplAMPrs1WW3RKVEAnI5qMc=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=IVHIXSMn0Zlrr79WpRoEVEcNmbntAjxuPQwWRdjtzimE3FfmeCdbAaOt36jL/02qv0d9gWqHja46A3qbqcIpoPC6FL6nKcAWJsxRjlw/R9V8W7PdXnBqH1k368yZgIJfNSYaCMP1ZXhMP9tMSf+lJDKCE6POEOGifvGp4aG2JBw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=PU2jRuaO; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="PU2jRuaO" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6CE801F000C4; Sat, 17 Oct 2026 16:48:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1792255726; bh=8SOfPmjWjzoSMshNwUYYuf6beFo/F7UmMRGS467CL+E=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=PU2jRuaOBaquNq1dP2tcRI7I1P9GpTIA83YIYOuEsK9LC9HoorHQLxOFDjGDS7BHf Ape3k7Dbe7FCuXYORHsOUd6+jrx74cskdCJjdzVlsaeEYhbumoX840IuKNU4IDrUmL /xrCPg8PzuZJaa67pmzT/IsiGu4wA8q/1qw56ZqE= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Max Kellermann , Viacheslav Dubeyko , Ilya Dryomov , Sasha Levin Subject: [PATCH 6.12 841/869] ceph: always call ceph_shift_unused_folios_left() Date: Sat, 17 Oct 2026 18:01:22 +0200 Message-ID: <20261017160058.432480493@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261017160036.979869304@linuxfoundation.org> References: <20261017160036.979869304@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Max Kellermann [ Upstream commit cce7c15faaac79b532a07ed6ab8332280ad83762 ] The function ceph_process_folio_batch() sets folio_batch entries to NULL, which is an illegal state. Before folio_batch_release() crashes due to this API violation, the function ceph_shift_unused_folios_left() is supposed to remove those NULLs from the array. However, since commit ce80b76dd327 ("ceph: introduce ceph_process_folio_batch() method"), this shifting doesn't happen anymore because the "for" loop got moved to ceph_process_folio_batch(), and now the `i` variable that remains in ceph_writepages_start() doesn't get incremented anymore, making the shifting effectively unreachable much of the time. Later, commit 1551ec61dc55 ("ceph: introduce ceph_submit_write() method") added more preconditions for doing the shift, replacing the `i` check (with something that is still just as broken): - if ceph_process_folio_batch() fails, shifting never happens - if ceph_move_dirty_page_in_page_array() was never called (because ceph_process_folio_batch() has returned early for some of various reasons), shifting never happens - if `processed_in_fbatch` is zero (because ceph_process_folio_batch() has returned early for some of the reasons mentioned above or because ceph_move_dirty_page_in_page_array() has failed), shifting never happens Since those two commits, any problem in ceph_process_folio_batch() could crash the kernel, e.g. this way: BUG: kernel NULL pointer dereference, address: 0000000000000034 #PF: supervisor write access in kernel mode #PF: error_code(0x0002) - not-present page PGD 0 P4D 0 Oops: Oops: 0002 [#1] SMP NOPTI CPU: 172 UID: 0 PID: 2342707 Comm: kworker/u778:8 Not tainted 6.15.10-cm4all1-es #714 NONE Hardware name: Dell Inc. PowerEdge R7615/0G9DHV, BIOS 1.6.10 12/08/2023 Workqueue: writeback wb_workfn (flush-ceph-1) RIP: 0010:folios_put_refs+0x85/0x140 Code: 83 c5 01 39 e8 7e 76 48 63 c5 49 8b 5c c4 08 b8 01 00 00 00 4d 85 ed 74 05 41 8b 44 ad 00 48 8b 15 b0 > RSP: 0018:ffffb880af8db778 EFLAGS: 00010207 RAX: 0000000000000001 RBX: 0000000000000000 RCX: 0000000000000003 RDX: ffffe377cc3b0000 RSI: 0000000000000000 RDI: ffffb880af8db8c0 RBP: 0000000000000000 R08: 000000000000007d R09: 000000000102b86f R10: 0000000000000001 R11: 00000000000000ac R12: ffffb880af8db8c0 R13: 0000000000000000 R14: 0000000000000000 R15: ffff9bd262c97000 FS: 0000000000000000(0000) GS:ffff9c8efc303000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000034 CR3: 0000000160958004 CR4: 0000000000770ef0 PKRU: 55555554 Call Trace: ceph_writepages_start+0xeb9/0x1410 The crash can be reproduced easily by changing the ceph_check_page_before_write() return value to `-E2BIG`. (Interestingly, the crash happens only if `huge_zero_folio` has already been allocated; without `huge_zero_folio`, is_huge_zero_folio(NULL) returns true and folios_put_refs() skips NULL entries instead of dereferencing them. That makes reproducing the bug somewhat unreliable. See https://lore.kernel.org/20250826231626.218675-1-max.kellermann@ionos.com for a discussion of this detail.) My suggestion is to move the ceph_shift_unused_folios_left() to right after ceph_process_folio_batch() to ensure it always gets called to fix up the illegal folio_batch state. Cc: stable@vger.kernel.org Fixes: ce80b76dd327 ("ceph: introduce ceph_process_folio_batch() method") Link: https://lore.kernel.org/ceph-devel/aK4v548CId5GIKG1@swift.blarg.de/ Signed-off-by: Max Kellermann Reviewed-by: Viacheslav Dubeyko Signed-off-by: Ilya Dryomov Signed-off-by: Sasha Levin --- fs/ceph/addr.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/fs/ceph/addr.c b/fs/ceph/addr.c index ded22f066128f..5e0f83adc4590 100644 --- a/fs/ceph/addr.c +++ b/fs/ceph/addr.c @@ -1682,6 +1682,7 @@ static int ceph_writepages_start(struct address_space *mapping, process_folio_batch: rc = ceph_process_folio_batch(mapping, wbc, &ceph_wbc); + ceph_shift_unused_folios_left(&ceph_wbc.fbatch); if (rc) goto release_folios; @@ -1690,8 +1691,6 @@ static int ceph_writepages_start(struct address_space *mapping, goto release_folios; if (ceph_wbc.processed_in_fbatch) { - ceph_shift_unused_folios_left(&ceph_wbc.fbatch); - if (folio_batch_count(&ceph_wbc.fbatch) == 0 && ceph_wbc.locked_pages < ceph_wbc.max_pages) { doutc(cl, "reached end fbatch, trying for more\n"); -- 2.53.0