From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794049395; b=IPTZEXFhAEExtFnehHUi8OPM+7DixNKtMVJhsCSpXY5+e6omNPffYLCX/imosWeN8DEI 7zIOykqgNT97LfQgQX17U7IvE5qnTu1vOdC4pLJKcKYI0pR7J+1sDHVSR9U2jM+4FQRbH HUHh4RpSQV0X0dhzvyt2C2J0+xN/oG0ALWMvFo3TQYOiRLatxy7GGo5cUvl80KfBHH3JC k0S2HNzj5BsY/cozzHn07Dd04/mnIU/4huAplgw223itaZxH2ntI4bjwhPelqP3B7jCSK ArCCLVSr9yBPpa8X0MPntlJxfACBdjEVcaGuCL6HWM6TkuCKu7ruwE+evXlncDl1GVA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794049395; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: MIME-Version:Content-Type:Content-Transfer-Encoding; bh=Jj2W2AHA2wGKiYNtDEa1hZPofpGl5IKMqwIr72+gTm8=; b=bD+MGgFdVQ9PJCXJlhThBKIz6bBKFvpFBN2S12VwshnabwLKl5sPjo661kUH++PAXMWq M1cEOL+hBqVB5qQOJPeWSX7Tij2ClXA/84CJ3nEAdvy+XtAtweJh9SuxSPS9HJA79YHfA uwGNiDhE1A9fO0DwllUJAIZk4/sEarutawoNqOrY4+r/aeX87EpnotS7d6XH+s7mhFG0Z ChBtmHXGq8oJ3SprOBlYW8zg65f3610CGsFnrZ7sHfL4GsOAUCIeCtEHCYrLbSTW5Qtbb 2VuxMXFB5BC3RDPYohG1IwhWPY8j6Fin2zWecd8Fs12mZshocGeFAQGBzn2OZH0pZFQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=bGm4Lurw; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 85666606A32D for ; Sat, 7 Nov 2026 11:03:15 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=bGm4Lurw Received: by smtp.kernel.org (Postfix) with ESMTPSA id CC3A11F0089F; Sat, 7 Nov 2026 11:03:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794049395; bh=Jj2W2AHA2wGKiYNtDEa1hZPofpGl5IKMqwIr72+gTm8=; h=From:To:Cc:Subject:Date; b=bGm4Lurw5GeVzDWfNYVSHwZUlwDHIBNC0y4/fuxwfwqmIL7vgjsCiKHmrNSBBGqT+ UGqByyJIoJT1ToASYjSPTBJuIPEyTjr8CnOWFwcTWFVq6KGgERbO5sEJrE9jguGF1m nzLazgQhE+1sam+SwbDTaVIMtTwDiOYHtC8hG9xep103DmtyHq5h/3jf2AkK/7eHZ6 MpRw6Ql41U9cni5If11eEUrU2geVut3z9A+n3qu1Unzu5ShjaQBukciOdO9HHrwq1N 0xgOJGcAb0G506sc6642czu03Qi3p2jOEge7NtjFuCAAw9jZ9N+GhYgfrs2YvSANu+ BghJwVIpcfMbg== From: Sasha Levin To: daejun7.park@samsung.com, junzheyu1@gmail.com, jack@suse.cz, tytso@mit.edu Cc: stable@vger.kernel.org Subject: FAILED: patch "[PATCH] jbd2: don't advance j_fc_off before the buffer is recorded" failed to apply to 5.15-stable tree Date: Sat, 7 Nov 2026 06:03:13 -0500 Message-ID: <20261107060313-failed-5.15-9f359c031885@kernel.org> X-Mailer: git-send-email 2.53.0 X-Mailing-List: stable@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The patch below does not apply to the 5.15-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y git checkout FETCH_HEAD git cherry-pick -x 9f359c031885bb50add7d23c7a5a0e9755b134c9 # git commit -s git send-email --to '' --in-reply-to '20261107060313-failed-5.15-9f359c031885@kernel.org' --subject-prefix 'PATCH 5.15.y' 'HEAD^..' Thanks, Sasha ------------------ original commit in Linus's tree ------------------ >From 9f359c031885bb50add7d23c7a5a0e9755b134c9 Mon Sep 17 00:00:00 2001 From: Daejun Park Date: Wed, 19 Aug 2026 15:09:39 +0900 Subject: [PATCH] jbd2: don't advance j_fc_off before the buffer is recorded jbd2_fc_get_buf() increments journal->j_fc_off before jbd2_journal_bmap() and __getblk() have had a chance to fail. When either does, the slot j_fc_wbuf[fc_off] is never assigned, but j_fc_off already counts it. ext4 then fails the fast commit and falls back, and the fallback path reaches jbd2_fc_release_bufs() via ext4_fc_commit -> jbd2_fc_end_commit_fallback -> __jbd2_fc_end_commit -> ext4_fc_cleanup. That walks down from j_fc_off - 1 and put_bh()es every slot until it sees NULL, so it also touches the slot that was never written. j_fc_wbuf comes from a plain kmalloc() and is never zeroed, so a slot used for the first time holds uninitialised heap data. Advance j_fc_off only after the buffer head has been stored. That restores the invariant that j_fc_off covers exactly the filled slots, which is what jbd2_fc_release_bufs() relies on: the live buffers of the current fast commit sit above the NULLs the previous one released, so stopping at the first NULL is correct. Reproduced on a KASAN kernel with an ext4 fast_commit filesystem on a loop device, truncating the backing file under the live mount so that only the journal's fast-commit region falls past the end of the device. __getblk() then fails for the first fast-commit block while the rest of the journal is still addressable, so the journal is not aborted and the fast commit reaches the fallback path. j_fc_wbuf was poisoned to make the read of the never-written slot visible: BUG: KASAN: wild-memory-access in jbd2_fc_release_bufs+0x6b/0xd0 Write of size 4 at addr 5a5a5a5a5a5a5ab2 by task sync/961 jbd2_fc_release_bufs+0x6b/0xd0 ext4_fc_cleanup+0x97/0x830 __jbd2_fc_end_commit+0x37/0xc0 ext4_fc_commit+0x524/0x560 ext4_sync_file+0x3c4/0x4b0 __x64_sys_fsync+0x20/0x30 With this patch the same run leaves j_fc_off at 0 across repeated __getblk() failures and completes cleanly. Fixes: ff780b91efe9 ("jbd2: add fast commit machinery") Cc: stable@kernel.org Reported-by: Yu Junzhe Closes: https://lore.kernel.org/linux-ext4/7e4b109d-64c3-444f-a5dc-93c2ca4576cc@gmail.com/ Signed-off-by: Daejun Park Reviewed-by: Jan Kara Link: https://patch.msgid.link/20260819060939epcms2p37bb8589b2f8a52a2b14bef38fadcf69d@epcms2p3 Signed-off-by: Theodore Ts'o --- fs/jbd2/journal.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c index 00f5a98f3d4fe..55b4ce0102289 100644 --- a/fs/jbd2/journal.c +++ b/fs/jbd2/journal.c @@ -843,7 +843,6 @@ int jbd2_fc_get_buf(journal_t *journal, struct buffer_head **bh_out) fc_off = journal->j_fc_off; blocknr = journal->j_fc_first + fc_off; - journal->j_fc_off++; ret = jbd2_journal_bmap(journal, blocknr, &pblock); if (ret) return ret; @@ -853,6 +852,7 @@ int jbd2_fc_get_buf(journal_t *journal, struct buffer_head **bh_out) return -ENOMEM; journal->j_fc_wbuf[fc_off] = bh; + journal->j_fc_off++; *bh_out = bh; -- 2.53.0