[PATCH v2 0/2] optimize ea_inode block expansion to fix panic

[PATCH v2 0/2] optimize ea_inode block expansion to fix panic

[Jun Nie]

Optimize ea_inode block expansion to avoid memcpy if possible,
panic can be avoided in this way too.

Change vs version 1:
Only error and warning log format in patch 2 is modified per
Theodore's suggestion.

Jun Nie (2):
  ext4: optimize ea_inode block expansion
  ext4: refuse to create ea block when umounted

 fs/ext4/xattr.c | 35 ++++++++++++++++++++++++-----------
 1 file changed, 24 insertions(+), 11 deletions(-)

-- 
2.34.1

[PATCH v2 1/2] ext4: optimize ea_inode block expansion

[Jun Nie]

Copy ea data from inode entry when expanding ea block if possible.
Then remove the ea entry if expansion success. Thus memcpy to a
temporary buffer may be avoided.

If the expansion fails, we do not need to recovery the removed ea
entry neither in this way.

Signed-off-by: Jun Nie <jun.nie@linaro.org>
---
 fs/ext4/xattr.c | 28 +++++++++++++++++-----------
 1 file changed, 17 insertions(+), 11 deletions(-)

diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
index 7decaaf27e82..235a517d9c17 100644
--- a/fs/ext4/xattr.c
+++ b/fs/ext4/xattr.c
@@ -2551,9 +2551,8 @@ static int ext4_xattr_move_to_block(handle_t *handle, struct inode *inode,
 
 	is = kzalloc(sizeof(struct ext4_xattr_ibody_find), GFP_NOFS);
 	bs = kzalloc(sizeof(struct ext4_xattr_block_find), GFP_NOFS);
-	buffer = kvmalloc(value_size, GFP_NOFS);
 	b_entry_name = kmalloc(entry->e_name_len + 1, GFP_NOFS);
-	if (!is || !bs || !buffer || !b_entry_name) {
+	if (!is || !bs || !b_entry_name) {
 		error = -ENOMEM;
 		goto out;
 	}
@@ -2565,12 +2564,18 @@ static int ext4_xattr_move_to_block(handle_t *handle, struct inode *inode,
 
 	/* Save the entry name and the entry value */
 	if (entry->e_value_inum) {
+		buffer = kvmalloc(value_size, GFP_NOFS);
+		if (!buffer) {
+			error = -ENOMEM;
+			goto out;
+		}
+
 		error = ext4_xattr_inode_get(inode, entry, buffer, value_size);
 		if (error)
 			goto out;
 	} else {
 		size_t value_offs = le16_to_cpu(entry->e_value_offs);
-		memcpy(buffer, (void *)IFIRST(header) + value_offs, value_size);
+		buffer = (void *)IFIRST(header) + value_offs;
 	}
 
 	memcpy(b_entry_name, entry->e_name, entry->e_name_len);
@@ -2585,25 +2590,26 @@ static int ext4_xattr_move_to_block(handle_t *handle, struct inode *inode,
 	if (error)
 		goto out;
 
-	/* Remove the chosen entry from the inode */
-	error = ext4_xattr_ibody_set(handle, inode, &i, is);
-	if (error)
-		goto out;
-
 	i.value = buffer;
 	i.value_len = value_size;
 	error = ext4_xattr_block_find(inode, &i, bs);
 	if (error)
 		goto out;
 
-	/* Add entry which was removed from the inode into the block */
+	/* Move ea entry from the inode into the block */
 	error = ext4_xattr_block_set(handle, inode, &i, bs);
 	if (error)
 		goto out;
-	error = 0;
+
+	/* Remove the chosen entry from the inode */
+	i.value = NULL;
+	i.value_len = 0;
+	error = ext4_xattr_ibody_set(handle, inode, &i, is);
+
 out:
 	kfree(b_entry_name);
-	kvfree(buffer);
+	if (entry->e_value_inum && buffer)
+		kvfree(buffer);
 	if (is)
 		brelse(is->iloc.bh);
 	if (bs)
-- 
2.34.1

[PATCH v2 2/2] ext4: refuse to create ea block when umounted

[Jun Nie]

The ea block expansion need to access s_root while it is
already set as NULL when umount is triggered. Refuse this
request to avoid panic.

Reported-by: syzbot+2dacb8f015bf1420155f@syzkaller.appspotmail.com
Link: https://syzkaller.appspot.com/bug?id=3613786cb88c93aa1c6a279b1df6a7b201347d08
Signed-off-by: Jun Nie <jun.nie@linaro.org>
---
 fs/ext4/xattr.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
index 235a517d9c17..b350510b798c 100644
--- a/fs/ext4/xattr.c
+++ b/fs/ext4/xattr.c
@@ -1422,6 +1422,13 @@ static struct inode *ext4_xattr_inode_create(handle_t *handle,
 	uid_t owner[2] = { i_uid_read(inode), i_gid_read(inode) };
 	int err;
 
+	if (inode->i_sb->s_root == NULL) {
+		ext4_warning(inode->i_sb,
+			     "refuse to create EA inode when umounting");
+		WARN_ON(1);
+		return ERR_PTR(-EINVAL);
+	}
+
 	/*
 	 * Let the next inode be the goal, so we try and allocate the EA inode
 	 * in the same group, or nearby one.
-- 
2.34.1

Re: [PATCH v2 0/2] optimize ea_inode block expansion to fix panic

[Theodore Ts'o]

On Tue, 3 Jan 2023 09:45:15 +0800, Jun Nie wrote:
> Optimize ea_inode block expansion to avoid memcpy if possible,
> panic can be avoided in this way too.
> 
> Change vs version 1:
> Only error and warning log format in patch 2 is modified per
> Theodore's suggestion.
> 
> [...]

Applied, thanks!

[1/2] ext4: optimize ea_inode block expansion
      commit: 1e9d62d252812575ded7c620d8fc67c32ff06c16
[2/2] ext4: refuse to create ea block when umounted
      commit: f31173c19901a96bb2ebf6bcfec8a08df7095c91

Best regards,
-- 
Theodore Ts'o <tytso@mit.edu>