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=1794064534; b=4W8rj3LEVoDAUcLGIprODEIQXydeVvKP85/RuiVukUDVEG/FOeLLjUIbSBRhW2/8zVjf PvDwPzIpuFzRimMba9KJ9yZon+nDG4S6PJPvT2rC1XDGbM/LQhyYwquEPXiQevjHsCCaw 6SV3jCGbAaqrB6O9lctw8djIwJWolh26Lk8tbyxmTFPFCPbvzR1YvB6SD+Whpjf5hDivq hKHZbxLgWPjfofaYQwgqpUS/U4ATUeu+LhIrKe1t2Xi1CjwdzxisxmgQYvcK6Yp7/7N+X DQEEV516kAyHcHfpgRjW03ZpkbcsFbuluW7KicJbdhVuHK/J378Jl+1Pu7pc92EZ+uA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794064534; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:User-Agent:X-stable:X-Patchwork-Hint: MIME-Version:Content-Transfer-Encoding; bh=yCVY46ei3w1Z6qN/GdNvDeyAGR0dToKd5/TF0bOop8c=; b=boSv1RzY2trkvNFYUS+sEDqSfSLkB5mFclzbNj0YFnmh9onqgYIuLvpDf4EbsaEmWvLE Mb1XFKZavncGhw3GluzEy2Fuo1i7m+Ez3hyQhw5V+De6Khb0/vreBzkXwUXmAblWyS0KF 1zHXFOEEsajtUhJ8lbsA4M3L3vDIdpXnDb88nG9lFOq2RwxEUjAg8VhFrW+k1MDuOUDI3 uMwwAYAiRzM9GWZTLogDpdXMqhpZ1zVeKsgM2r2+uttDDoJX3RMNZcMK+r9cgOzU33/nf 7ACwGZxt9epXG9o4GjNqseaBz8Z9GcrONPh+apkBy/6Vu91Hk5wMBT+PftBeRFPdg+Q== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=snzn2ZUh; 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 7C1D7606B8A6; Sat, 7 Nov 2026 15:15:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=snzn2ZUh Received: by smtp.kernel.org (Postfix) with ESMTPSA id D83441F008A2; Sat, 7 Nov 2026 15:15:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1794064534; bh=yCVY46ei3w1Z6qN/GdNvDeyAGR0dToKd5/TF0bOop8c=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=snzn2ZUhtBDq+QsdwpeHTIEnLoa8d7Rz5iJe88EKmJYNiV9Wm5rzj6S86/HeWoKeh 77M8hwmQMDLOVjVAOBqTahoPhuX7HGtLzRtO+rDCnt5+HCGde9sTbyNlJvJgD9yG37 irKxqMg2sEKtwfdU6VsxBokLRemWSsRKImJTTlKQ= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, stable@kernel.org, Yu Junzhe , Daejun Park , Jan Kara , Theodore Tso , Sasha Levin Subject: [PATCH 7.3 0562/1257] jbd2: dont advance j_fc_off before the buffer is recorded Date: Sat, 7 Nov 2026 08:47:38 -0500 Message-ID: <20261107134954.893232325@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261107134939.434104957@linuxfoundation.org> References: <20261107134939.434104957@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore 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-Transfer-Encoding: 8bit 7.3-stable review patch. If anyone has any objections, please let me know. ------------------ From: Daejun Park [ Upstream commit 9f359c031885bb50add7d23c7a5a0e9755b134c9 ] 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 Signed-off-by: Sasha Levin --- 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