FAILED: patch "[PATCH] f2fs: read COW data with the original inode during atomic" failed to apply to 6.12-stable tree

PATCH New [email protected] 2 participants 2 messages Jul 2 – Jul 3

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2026-07-02 13:11 UTC #0 lore raw

The patch below does not apply to the 6.12-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 <[email protected]>.

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-6.12.y
git checkout FETCH_HEAD
git cherry-pick -x a41075acde0124d2f8a5f563068a5d63e8ffd57b
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026070221-snort-vantage-43cb@gregkh' --subject-prefix 'PATCH 6.12.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From a41075acde0124d2f8a5f563068a5d63e8ffd57b Mon Sep 17 00:00:00 2001
From: Mikhail Lobanov <[email protected]>
Date: Mon, 15 Jun 2026 14:36:13 +0300
Subject: [PATCH] f2fs: read COW data with the original inode during atomic
write

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 [email protected]

Signed-off-by Mikhail Lobanov <[email protected]>

Reviewed-by Chao Yu <[email protected]>

Signed-off-by Jaegeuk Kim <[email protected]>

fs/f2fs/data.c +16 ~~-10~~

index cea34b4595b1..60dea95b0295 100644
@@ -3860,7 +3860,7 @@ 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;

@@ -3875,14 +3875,14 @@ 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 (__is_valid_data_blkaddr(*blk_addr)) {
-		*use_cow = true;
+
+	if (__is_valid_data_blkaddr(*blk_addr))
 		return 0;
-	} else if (*blk_addr == NEW_ADDR) {
+
+	if (*blk_addr == NEW_ADDR)
 		cow_has_reserved_block = true;
-	}
 
 	if (is_inode_flag_set(inode, FI_ATOMIC_REPLACE))
 		goto reserve_block;

@@ -3917,7 +3917,6 @@ 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;

@@ -3980,7 +3979,7 @@ 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);

@@ -4020,8 +4019,15 @@ 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,
+		/*
+		 * 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,
 				      NULL, /* can't write to fsverity files */
 				      folio, blkaddr, 0, true);

Sasha Levin

maintainer

2026-07-03 14:26 UTC #1 lore raw

PATCH 1/1 f2fs: read COW data with the original inode during atomic write

From: Mikhail Lobanov <[email protected]>

[ Upstream commit a41075acde0124d2f8a5f563068a5d63e8ffd57b ]

	f2fs_submit_page_read(use_cow ? F2FS_I(inode)->cow_inode : inode,
			      ...);