linux-kernel - [PATCH 5.12 292/384] f2fs: fix error handling in f2fs_end_enable

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Date:   Mon, 10 May 2021 12:21:21 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Yunlei He <heyunlei@...onor.com>,
        Eric Biggers <ebiggers@...gle.com>,
        Chao Yu <yuchao0@...wei.com>, Jaegeuk Kim <jaegeuk@...nel.org>
Subject: [PATCH 5.12 292/384] f2fs: fix error handling in f2fs_end_enable_verity()

From: Eric Biggers <ebiggers@...gle.com>

commit 3c0315424f5e3d2a4113c7272367bee1e8e6a174 upstream.

f2fs didn't properly clean up if verity failed to be enabled on a file:

- It left verity metadata (pages past EOF) in the page cache, which
  would be exposed to userspace if the file was later extended.

- It didn't truncate the verity metadata at all (either from cache or
  from disk) if an error occurred while setting the verity bit.

Fix these bugs by adding a call to truncate_inode_pages() and ensuring
that we truncate the verity metadata (both from cache and from disk) in
all error paths.  Also rework the code to cleanly separate the success
path from the error paths, which makes it much easier to understand.

Finally, log a message if f2fs_truncate() fails, since it might
otherwise fail silently.

Reported-by: Yunlei He <heyunlei@...onor.com>
Fixes: 95ae251fe828 ("f2fs: add fs-verity support")
Cc: <stable@...r.kernel.org> # v5.4+
Signed-off-by: Eric Biggers <ebiggers@...gle.com>
Reviewed-by: Chao Yu <yuchao0@...wei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 fs/f2fs/verity.c |   79 ++++++++++++++++++++++++++++++++++++++-----------------
 1 file changed, 56 insertions(+), 23 deletions(-)

--- a/fs/f2fs/verity.c
+++ b/fs/f2fs/verity.c
@@ -152,40 +152,73 @@ static int f2fs_end_enable_verity(struct
 				  size_t desc_size, u64 merkle_tree_size)
 {
 	struct inode *inode = file_inode(filp);
+	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
 	u64 desc_pos = f2fs_verity_metadata_pos(inode) + merkle_tree_size;
 	struct fsverity_descriptor_location dloc = {
 		.version = cpu_to_le32(F2FS_VERIFY_VER),
 		.size = cpu_to_le32(desc_size),
 		.pos = cpu_to_le64(desc_pos),
 	};
-	int err = 0;
+	int err = 0, err2 = 0;
 
-	if (desc != NULL) {
-		/* Succeeded; write the verity descriptor. */
-		err = pagecache_write(inode, desc, desc_size, desc_pos);
-
-		/* Write all pages before clearing FI_VERITY_IN_PROGRESS. */
-		if (!err)
-			err = filemap_write_and_wait(inode->i_mapping);
-	}
-
-	/* If we failed, truncate anything we wrote past i_size. */
-	if (desc == NULL || err)
-		f2fs_truncate(inode);
+	/*
+	 * If an error already occurred (which fs/verity/ signals by passing
+	 * desc == NULL), then only clean-up is needed.
+	 */
+	if (desc == NULL)
+		goto cleanup;
+
+	/* Append the verity descriptor. */
+	err = pagecache_write(inode, desc, desc_size, desc_pos);
+	if (err)
+		goto cleanup;
+
+	/*
+	 * Write all pages (both data and verity metadata).  Note that this must
+	 * happen before clearing FI_VERITY_IN_PROGRESS; otherwise pages beyond
+	 * i_size won't be written properly.  For crash consistency, this also
+	 * must happen before the verity inode flag gets persisted.
+	 */
+	err = filemap_write_and_wait(inode->i_mapping);
+	if (err)
+		goto cleanup;
+
+	/* Set the verity xattr. */
+	err = f2fs_setxattr(inode, F2FS_XATTR_INDEX_VERITY,
+			    F2FS_XATTR_NAME_VERITY, &dloc, sizeof(dloc),
+			    NULL, XATTR_CREATE);
+	if (err)
+		goto cleanup;
+
+	/* Finally, set the verity inode flag. */
+	file_set_verity(inode);
+	f2fs_set_inode_flags(inode);
+	f2fs_mark_inode_dirty_sync(inode, true);
 
 	clear_inode_flag(inode, FI_VERITY_IN_PROGRESS);
+	return 0;
 
-	if (desc != NULL && !err) {
-		err = f2fs_setxattr(inode, F2FS_XATTR_INDEX_VERITY,
-				    F2FS_XATTR_NAME_VERITY, &dloc, sizeof(dloc),
-				    NULL, XATTR_CREATE);
-		if (!err) {
-			file_set_verity(inode);
-			f2fs_set_inode_flags(inode);
-			f2fs_mark_inode_dirty_sync(inode, true);
-		}
+cleanup:
+	/*
+	 * Verity failed to be enabled, so clean up by truncating any verity
+	 * metadata that was written beyond i_size (both from cache and from
+	 * disk) and clearing FI_VERITY_IN_PROGRESS.
+	 *
+	 * Taking i_gc_rwsem[WRITE] is needed to stop f2fs garbage collection
+	 * from re-instantiating cached pages we are truncating (since unlike
+	 * normal file accesses, garbage collection isn't limited by i_size).
+	 */
+	down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
+	truncate_inode_pages(inode->i_mapping, inode->i_size);
+	err2 = f2fs_truncate(inode);
+	if (err2) {
+		f2fs_err(sbi, "Truncating verity metadata failed (errno=%d)",
+			 err2);
+		set_sbi_flag(sbi, SBI_NEED_FSCK);
 	}
-	return err;
+	up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
+	clear_inode_flag(inode, FI_VERITY_IN_PROGRESS);
+	return err ?: err2;
 }
 
 static int f2fs_get_verity_descriptor(struct inode *inode, void *buf,