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 5E5203D7D7F for ; Fri, 3 Jul 2026 14:09:14 +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=1783087755; cv=none; b=mlRTx/1flU6749y0T081C7QcZBBckZTycyKviaYc96GeafkLDMHmCI/cFH2kRyM+ll71hv6osKBPSMFHizUiorSvGfvQDywuDGRIi3qBQwiyLPrhusc9VOaOXcMMg4owbpYSWaIdpOanT9J+4av+ooM1yOfJ46F83iClBuSnuM8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783087755; c=relaxed/simple; bh=oG9IchSUavvlz6eo3z5L2oHEVExiuGwCINZDbakCgw0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=C9kZzhA7Ba0CiChRxftJA1vh8iuyV7HiWKhyvi42XYCWKpyM7toPIpLM4q1L+vTCTtAHNAEQO55KW5S6SKHWV+mf+ONAWjnDJ8ahKRyAapKBLmV64r+StCSAAE8CXuXaouSc6OjrahBjYi2JI8Fg6T8NJkso1uNqw/57zJgH62U= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=FZlsFDbC; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="FZlsFDbC" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 568061F000E9; Fri, 3 Jul 2026 14:09:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783087754; bh=ddlNMlX2UPDC8A0nNdDdpqbl4ff+62gLmVr0DVAr/JM=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=FZlsFDbCwjDjno95rlwmSMnifl1b6mguisuG75p0YEKZ8zUVH3iTuLfN8o9ACwsxr bfb99/JWGj1GMgXJeCx3n+X0gz3D8TCKSN0gjSCmehrlIH3yFMI4oFFr9UYyy0sVZG 6tbhmorPiu4bS9iRzn4DeFz8NLTkabyTicizclelzZLLFkgzYGxDcRRh2fiBWn3qCE cpMB1MbPh2WfTrM1ATRFz132XYP202IHNZC0+noMwM0pJgHS/4Do0tyyT3bffV184D +NPdRpXDJpN9Vjp044hPn6KB9YGaqjqWSdQkDa7hK0L/w8MEk0zQw3vFrguQrdniAh AlutgOItwx/0A== From: Sasha Levin To: stable@vger.kernel.org Cc: Mikhail Lobanov , Chao Yu , Jaegeuk Kim , Sasha Levin Subject: [PATCH 6.18.y] f2fs: read COW data with the original inode during atomic write Date: Fri, 3 Jul 2026 10:09:11 -0400 Message-ID: <20260703140911.17045-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <2026070220-thirstily-deniable-6715@gregkh> References: <2026070220-thirstily-deniable-6715@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Mikhail Lobanov [ Upstream commit a41075acde0124d2f8a5f563068a5d63e8ffd57b ] When updating an atomic-write file, f2fs_write_begin() may read the previously written data back from the COW inode: prepare_atomic_write_begin() locates the block in the COW inode and sets use_cow, and the read bio is then built with the COW inode: f2fs_submit_page_read(use_cow ? F2FS_I(inode)->cow_inode : inode, ...); and f2fs_grab_read_bio() decides whether to schedule fs-layer decryption (STEP_DECRYPT) for the bio based on that inode via fscrypt_inode_uses_fs_layer_crypto(). However, the folio being filled belongs to the original inode (folio->mapping->host == inode), and the data stored in the COW block was encrypted (or left as plaintext) using the original inode's context, not the COW inode's -- see f2fs_encrypt_one_page(), which keys off fio->page->mapping->host. fscrypt_decrypt_pagecache_blocks() likewise operates on folio->mapping->host. The COW inode is created as a tmpfile in the parent directory and inherits its encryption policy from there. With test_dummy_encryption the newly created COW inode gets the dummy policy and becomes encrypted, while a pre-existing regular file -- created before the policy applied, e.g. already present in the on-disk image -- stays unencrypted. The read path then sets STEP_DECRYPT based on the encrypted COW inode and calls fscrypt_decrypt_pagecache_blocks() on a folio whose host (the unencrypted original inode) has a NULL ->i_crypt_info, dereferencing it: Oops: general protection fault, probably for non-canonical address ... KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f] RIP: 0010:fscrypt_decrypt_pagecache_blocks+0xa0/0x310 Workqueue: f2fs_post_read_wq f2fs_post_read_work Call Trace: fscrypt_decrypt_bio+0x1eb/0x340 f2fs_post_read_work+0xba/0x140 process_one_work+0x91c/0x1a40 worker_thread+0x677/0xe90 kthread+0x2bc/0x3a0 The COW inode is only needed to locate the on-disk block, and that block address is already resolved into @blkaddr by prepare_atomic_write_begin() via __find_data_block(cow_inode, ...); f2fs_submit_page_read() then reads from that physical @blkaddr directly, so the inode argument only selects the post-read crypto context, not which block is fetched. Reading with @inode therefore returns the same (latest, not-yet-committed) COW data, while making both the fs-layer decryption decision and the inline crypto path use the correct (original inode's) key. With the COW inode no longer used at the read site, the use_cow flag has no remaining consumer; drop it from f2fs_write_begin() and prepare_atomic_write_begin(). Fixes: 591fc34e1f98 ("f2fs: use cow inode data when updating atomic write") Cc: stable@vger.kernel.org Signed-off-by: Mikhail Lobanov Reviewed-by: Chao Yu Signed-off-by: Jaegeuk Kim Signed-off-by: Sasha Levin --- fs/f2fs/data.c | 24 ++++++++++++++---------- 1 file changed, 14 insertions(+), 10 deletions(-) diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c index f468cba89f303b..b49e020181a6a4 100644 --- a/fs/f2fs/data.c +++ b/fs/f2fs/data.c @@ -3530,7 +3530,7 @@ static int __reserve_data_block(struct inode *inode, pgoff_t index, static int prepare_atomic_write_begin(struct f2fs_sb_info *sbi, struct folio *folio, loff_t pos, unsigned int len, - block_t *blk_addr, bool *node_changed, bool *use_cow) + block_t *blk_addr, bool *node_changed) { struct inode *inode = folio->mapping->host; struct inode *cow_inode = F2FS_I(inode)->cow_inode; @@ -3544,12 +3544,11 @@ static int prepare_atomic_write_begin(struct f2fs_sb_info *sbi, /* Look for the block in COW inode first */ err = __find_data_block(cow_inode, index, blk_addr); - if (err) { + if (err) return err; - } else if (*blk_addr != NULL_ADDR) { - *use_cow = true; + + if (*blk_addr != NULL_ADDR) return 0; - } if (is_inode_flag_set(inode, FI_ATOMIC_REPLACE)) goto reserve_block; @@ -3581,7 +3580,6 @@ static int f2fs_write_begin(const struct kiocb *iocb, struct folio *folio; pgoff_t index = pos >> PAGE_SHIFT; bool need_balance = false; - bool use_cow = false; block_t blkaddr = NULL_ADDR; int err = 0; @@ -3643,7 +3641,7 @@ static int f2fs_write_begin(const struct kiocb *iocb, if (f2fs_is_atomic_file(inode)) err = prepare_atomic_write_begin(sbi, folio, pos, len, - &blkaddr, &need_balance, &use_cow); + &blkaddr, &need_balance); else err = prepare_write_begin(sbi, folio, pos, len, &blkaddr, &need_balance); @@ -3683,9 +3681,15 @@ static int f2fs_write_begin(const struct kiocb *iocb, err = -EFSCORRUPTED; goto put_folio; } - f2fs_submit_page_read(use_cow ? - F2FS_I(inode)->cow_inode : inode, - folio, blkaddr, 0, true); + /* + * Although the block may be stored in the COW inode, the folio + * belongs to @inode and its data was encrypted (or not) using + * @inode's context (see f2fs_encrypt_one_page()). Read with + * @inode so the post-read decryption decision matches the + * folio's owner; otherwise an unencrypted @inode whose COW inode + * is encrypted hits a NULL ->i_crypt_info on decryption. + */ + f2fs_submit_page_read(inode, folio, blkaddr, 0, true); folio_lock(folio); if (unlikely(folio->mapping != mapping)) { -- 2.53.0