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 57E591E1C11 for ; Fri, 3 Jul 2026 18:03:29 +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=1783101810; cv=none; b=mKCveXPAJGUR50UFuHOUBOe5oNmy++cZvpibQH1Fq8bSNicimpdOLomJsj2J1z3JkhpuZjXEYVeoVNOWBGf6I1wRNO9F4AaoYo9DS3IMXoqwBwahG8EGu2XVpvrwG09nXWlCDDtJjxtbz6oBxFPQa0J3uh+TxjhVLQVQVcB/9pk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783101810; c=relaxed/simple; bh=PlHWWAWQSqZWeoYoS0UYuGLlI3IKCJBq/6yYi2Ji4Zo=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Lwg/RU0OD3h4fqcuSQlnjhynquKRMVmSvJ+AgL3F4+Nl7cuvLp+VBTBON/P4k4GcYTi8K09xDQYQCBSgUD+RDCZtWIAMu6mqk8AbTJ0xZHvdeKwBfLwY6PP9RfGIcCHYY4QwzE/HPdAl6EgL9ADHZ6Fbim53Ejq8ZxtFuh11ivI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Q4CiRD3g; 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="Q4CiRD3g" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 58B7C1F000E9; Fri, 3 Jul 2026 18:03:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783101809; bh=dYBlPZ8SfipkXXwRbO5qKTrOxqHgqJ5Bs4kmrVdA1iY=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=Q4CiRD3g0BsfI4f6fuW3ytMWcsWSaL2Xhg1b4P4OlB+U6r8wZw9TB2joJ9/XYIsOC MuC6ryhpJDvfjG3ucqPjEpmKrmUZsCDLlMDdeltARCCcOhqrs21vemCM80QPPCT+N0 uxrt3dfXtYhhQs78f+A2oi6QNcsvzzIuSuVHRZUECwhVXm3NTG5CXrydlMpCr4i2yX GcwfZzigWvncQN9WN/6sl4kgaoWyy3gSqosOmbteTULSxCrzdQ1ub/htt3Nc7jQVkI C9/g7AAtwVaaiSwl7LXlTUvDzx1W5yHUYVR408jehUJcbwD9h8n3eQIozb3KT+8YOe 29XHi3lfUERPg== From: Sasha Levin To: stable@vger.kernel.org Cc: Mikhail Lobanov , Chao Yu , Jaegeuk Kim , Sasha Levin Subject: [PATCH 6.6.y] f2fs: read COW data with the original inode during atomic write Date: Fri, 3 Jul 2026 14:03:26 -0400 Message-ID: <20260703180326.197018-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <2026070221-botany-scale-ddf0@gregkh> References: <2026070221-botany-scale-ddf0@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 7643c1d7dbb273..22446e4437bdba 100644 --- a/fs/f2fs/data.c +++ b/fs/f2fs/data.c @@ -3520,7 +3520,7 @@ static int __reserve_data_block(struct inode *inode, pgoff_t index, static int prepare_atomic_write_begin(struct f2fs_sb_info *sbi, struct page *page, 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 = page->mapping->host; struct inode *cow_inode = F2FS_I(inode)->cow_inode; @@ -3534,12 +3534,11 @@ 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; @@ -3569,7 +3568,6 @@ static int f2fs_write_begin(struct file *file, struct address_space *mapping, struct page *page = NULL; pgoff_t index = ((unsigned long long) pos) >> PAGE_SHIFT; bool need_balance = false; - bool use_cow = false; block_t blkaddr = NULL_ADDR; int err = 0; @@ -3629,7 +3627,7 @@ static int f2fs_write_begin(struct file *file, struct address_space *mapping, if (f2fs_is_atomic_file(inode)) err = prepare_atomic_write_begin(sbi, page, pos, len, - &blkaddr, &need_balance, &use_cow); + &blkaddr, &need_balance); else err = prepare_write_begin(sbi, page, pos, len, &blkaddr, &need_balance); @@ -3669,9 +3667,15 @@ static int f2fs_write_begin(struct file *file, struct address_space *mapping, f2fs_handle_error(sbi, ERROR_INVALID_BLKADDR); goto fail; } - err = f2fs_submit_page_read(use_cow ? - F2FS_I(inode)->cow_inode : inode, page, - blkaddr, 0, true); + /* + * Although the block may be stored in the COW inode, the page + * 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 + * page's owner; otherwise an unencrypted @inode whose COW inode + * is encrypted hits a NULL ->i_crypt_info on decryption. + */ + err = f2fs_submit_page_read(inode, page, blkaddr, 0, true); if (err) goto fail; -- 2.53.0