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fs-verity: fix error handling in ->end_enable_verity()

PATCH In review Eric Biggers 3 participants 6 messages Mar 2, 2021 – Mar 11, 2021

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Eric Biggers

author maintainer
#0 lore raw

cover fs-verity: fix error handling in ->end_enable_verity()

Fix some bugs in how ext4_end_enable_verity() and f2fs_end_enable_verity() handle failure to enable verity on the file.

This is intended to supersede the f2fs patch from Yunlei He
(https://lore.kernel.org/r/[email protected],
https://lore.kernel.org/r/[email protected],
https://lore.kernel.org/r/[email protected]).
I fixed the same bugs in ext4 too, reworked the functions to cleanly separate the success and error paths, and improved the commit message.

These patches can be taken independently via the ext4 and f2fs trees. I've just sent them out together since they're similar.

Eric Biggers (2):
ext4: fix error handling in ext4_end_enable_verity()
f2fs: fix error handling in f2fs_end_enable_verity()

 fs/ext4/verity.c | 90 ++++++++++++++++++++++++++++++------------------
 fs/f2fs/verity.c | 61 +++++++++++++++++++++-----------
 2 files changed, 97 insertions(+), 54 deletions(-)
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2.30.1



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author maintainer
#1 lore raw

PATCH 1/2 ext4: fix error handling in ext4_end_enable_verity()

From: Eric Biggers <[email protected]>

ext4 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.

Fixes c93d8f885809 ("ext4: add basic fs-verity support")
Cc <[email protected]> # v5.4+
---
 fs/ext4/verity.c | 90 ++++++++++++++++++++++++++++++------------------
 1 file changed, 56 insertions(+), 34 deletions(-)
fs/ext4/verity.c +56 -34
index 5b7ba8f711538..acb12441c549b 100644
@@ -201,55 +201,77 @@ static int ext4_end_enable_verity(struct file *filp, const void *desc,
 	struct inode *inode = file_inode(filp);
 	const int credits = 2; /* superblock and inode for ext4_orphan_del() */
 	handle_t *handle;
+	struct ext4_iloc iloc;
 	int err = 0;
-	int err2;
 
-	if (desc != NULL) {
-		/* Succeeded; write the verity descriptor. */
-		err = ext4_write_verity_descriptor(inode, desc, desc_size,
-						   merkle_tree_size);
-
-		/* Write all pages before clearing VERITY_IN_PROGRESS. */
-		if (!err)
-			err = filemap_write_and_wait(inode->i_mapping);
-	}
+	/*
+	 * If an error already occurred (which fs/verity/ signals by passing
+	 * desc == NULL), then only clean-up is needed.
+	 */
+	if (desc == NULL)
+		goto cleanup;
 
-	/* If we failed, truncate anything we wrote past i_size. */
-	if (desc == NULL || err)
-		ext4_truncate(inode);
+	/* Append the verity descriptor. */
+	err = ext4_write_verity_descriptor(inode, desc, desc_size,
+					   merkle_tree_size);
+	if (err)
+		goto cleanup;
 
 	/*
-	 * We must always clean up by clearing EXT4_STATE_VERITY_IN_PROGRESS and
-	 * deleting the inode from the orphan list, even if something failed.
-	 * If everything succeeded, we'll also set the verity bit in the same
-	 * transaction.
+	 * Write all pages (both data and verity metadata).  Note that this must
+	 * happen before clearing EXT4_STATE_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;
 
-	ext4_clear_inode_state(inode, EXT4_STATE_VERITY_IN_PROGRESS);
+	/*
+	 * Finally, set the verity inode flag and remove the inode from the
+	 * orphan list (in a single transaction).
+	 */
 
 	handle = ext4_journal_start(inode, EXT4_HT_INODE, credits);
 	if (IS_ERR(handle)) {
-		ext4_orphan_del(NULL, inode);
-		return PTR_ERR(handle);
+		err = PTR_ERR(handle);
+		goto cleanup;
 	}
 
-	err2 = ext4_orphan_del(handle, inode);
-	if (err2)
-		goto out_stop;
+	err = ext4_orphan_del(handle, inode);
+	if (err)
+		goto stop_and_cleanup;
 
-	if (desc != NULL && !err) {
-		struct ext4_iloc iloc;
+	err = ext4_reserve_inode_write(handle, inode, &iloc);
+	if (err)
+		goto stop_and_cleanup;
+
+	ext4_set_inode_flag(inode, EXT4_INODE_VERITY);
+	ext4_set_inode_flags(inode, false);
+	err = ext4_mark_iloc_dirty(handle, inode, &iloc);
+	if (err)
+		goto stop_and_cleanup;
 
-		err = ext4_reserve_inode_write(handle, inode, &iloc);
-		if (err)
-			goto out_stop;
-		ext4_set_inode_flag(inode, EXT4_INODE_VERITY);
-		ext4_set_inode_flags(inode, false);
-		err = ext4_mark_iloc_dirty(handle, inode, &iloc);
-	}
-out_stop:
 	ext4_journal_stop(handle);
-	return err ?: err2;
+
+	ext4_clear_inode_state(inode, EXT4_STATE_VERITY_IN_PROGRESS);
+	return 0;
+
+
+stop_and_cleanup:
+	ext4_journal_stop(handle);
+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), removing the inode from the orphan list (if it wasn't done
+	 * already), and clearing EXT4_STATE_VERITY_IN_PROGRESS.
+	 */
+	truncate_inode_pages(inode->i_mapping, inode->i_size);
+	ext4_truncate(inode);
+	ext4_orphan_del(NULL, inode);
+	ext4_clear_inode_state(inode, EXT4_STATE_VERITY_IN_PROGRESS);
+	return err;
 }
 
 static int ext4_get_verity_descriptor_location(struct inode *inode,
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#2 lore raw

Re: [PATCH 1/2] ext4: fix error handling in ext4_end_enable_verity()

Quoted 15 lines · Eric Biggers

From: Eric Biggers <[email protected]>

ext4 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.

Quoted 4 lines
Fixes c93d8f885809 ("ext4: add basic fs-verity support")
Cc <[email protected]> # v5.4+

Thanks, LGTM.

I've applied this to the ext4 with minor adjustment; I eliminated the double blank line here:

fs/ext4/verity.c static int ext4_end_enable_verity(struct file *filp, const void *desc, · line 262

Quoted 6 lines
fs/ext4/verity.c +6 -0
+	ext4_clear_inode_state(inode, EXT4_STATE_VERITY_IN_PROGRESS);
+	return 0;
+
+
+stop_and_cleanup:
+	ext4_journal_stop(handle);

...

- Ted

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author maintainer
#3 lore raw

PATCH 2/2 f2fs: fix error handling in f2fs_end_enable_verity()

In reply to Eric Biggers

From: Eric Biggers <[email protected]>

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.

Fixes 95ae251fe828 ("f2fs: add fs-verity support")
Cc <[email protected]> # v5.4+
---
 fs/f2fs/verity.c | 61 ++++++++++++++++++++++++++++++++----------------
 1 file changed, 41 insertions(+), 20 deletions(-)
fs/f2fs/verity.c +41 -20
index 054ec852b5ea4..2db89967fde37 100644
@@ -160,31 +160,52 @@ static int f2fs_end_enable_verity(struct file *filp, const void *desc,
 	};
 	int err = 0;
 
-	if (desc != NULL) {
-		/* Succeeded; write the verity descriptor. */
-		err = pagecache_write(inode, desc, desc_size, desc_pos);
+	/*
+	 * If an error already occurred (which fs/verity/ signals by passing
+	 * desc == NULL), then only clean-up is needed.
+	 */
+	if (desc == NULL)
+		goto cleanup;
 
-		/* Write all pages before clearing FI_VERITY_IN_PROGRESS. */
-		if (!err)
-			err = filemap_write_and_wait(inode->i_mapping);
-	}
+	/* Append the verity descriptor. */
+	err = pagecache_write(inode, desc, desc_size, desc_pos);
+	if (err)
+		goto cleanup;
 
-	/* If we failed, truncate anything we wrote past i_size. */
-	if (desc == NULL || err)
-		f2fs_truncate(inode);
+	/*
+	 * 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.
+	 */
+	truncate_inode_pages(inode->i_mapping, inode->i_size);
+	f2fs_truncate(inode);
+	clear_inode_flag(inode, FI_VERITY_IN_PROGRESS);
 	return err;
 }
 
Signature · 8 lines
2.30.1



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#4 lore raw

Re: [f2fs-dev] [PATCH 2/2] f2fs: fix error handling in f2fs_end_enable_verity()

Quoted 86 lines · Eric Biggers

From: Eric Biggers <[email protected]>

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.

Fixes 95ae251fe828 ("f2fs: add fs-verity support")
Cc <[email protected]> # v5.4+
---
  fs/f2fs/verity.c | 61 ++++++++++++++++++++++++++++++++----------------
  1 file changed, 41 insertions(+), 20 deletions(-)
fs/f2fs/verity.c +32 -18
index 054ec852b5ea4..2db89967fde37 100644
@@ -160,31 +160,52 @@ static int f2fs_end_enable_verity(struct file *filp, const void *desc,
  	};
  	int err = 0;
 
-	if (desc != NULL) {
-		/* Succeeded; write the verity descriptor. */
-		err = pagecache_write(inode, desc, desc_size, desc_pos);
+	/*
+	 * If an error already occurred (which fs/verity/ signals by passing
+	 * desc == NULL), then only clean-up is needed.
+	 */
+	if (desc == NULL)
+		goto cleanup;
 
-		/* Write all pages before clearing FI_VERITY_IN_PROGRESS. */
-		if (!err)
-			err = filemap_write_and_wait(inode->i_mapping);
-	}
+	/* Append the verity descriptor. */
+	err = pagecache_write(inode, desc, desc_size, desc_pos);
+	if (err)
+		goto cleanup;
 
-	/* If we failed, truncate anything we wrote past i_size. */
-	if (desc == NULL || err)
-		f2fs_truncate(inode);
+	/*
+	 * 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);

fs/f2fs/verity.c static int f2fs_end_enable_verity(struct file *filp, const void *desc, · line 207

Quoted 10 lines
fs/f2fs/verity.c +8 -2
-		}
-	}
+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.
+	 */
+	truncate_inode_pages(inode->i_mapping, inode->i_size);
+	f2fs_truncate(inode);

Eric,

Truncation can fail due to a lot of reasons, if we fail in f2fs_truncate(), do we need to at least print a message here? or it allows to keep those meta/data silently.

One other concern is that how do you think of covering truncate_inode_pages & f2fs_truncate with F2FS_I(inode)->i_gc_rwsem[WRITE] lock to avoid racing with GC, so that page cache won't be revalidated after truncate_inode_pages().

Thanks,

Quoted 4 lines
fs/f2fs/verity.c +1 -0
+	clear_inode_flag(inode, FI_VERITY_IN_PROGRESS); >   	return err;
  }
 
 
author maintainer
#5 lore raw

Re: [PATCH 2/2] f2fs: fix error handling in f2fs_end_enable_verity()

Quoted 11 lines · Chao Yu

fs/f2fs/verity.c static int f2fs_end_enable_verity(struct file *filp, const void *desc, · line 207

Quoted 8 lines
fs/f2fs/verity.c +8 -0
+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.
+	 */
+	truncate_inode_pages(inode->i_mapping, inode->i_size);
+	f2fs_truncate(inode);

Eric,

Quoted 3 lines

Truncation can fail due to a lot of reasons, if we fail in f2fs_truncate(), do we need to at least print a message here? or it allows to keep those meta/data silently.

I suppose we might as well, although hopefully there will already be a message for the underlying failure reason too. Also, f2fs_file_write_iter() has the same issue too, right?

Quoted 3 lines

One other concern is that how do you think of covering truncate_inode_pages & f2fs_truncate with F2FS_I(inode)->i_gc_rwsem[WRITE] lock to avoid racing with GC, so that page cache won't be revalidated after truncate_inode_pages().

Yes, that does seem to be needed, due to the way the f2fs garbage collection works.

- Eric