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Date: Tue, 25 Sep 2012 08:38:00 +0200
From: Andreas Dilger <adilger@...mcloud.com>
To: Carlos Maiolino <cmaiolino@...hat.com>
Cc: "linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH] ext4: ext4_bread usage audit
On 2012-09-24, at 20:41, Carlos Maiolino <cmaiolino@...hat.com> wrote:
> Audit the usage of ext4_bread() due a possible misinterpretion of its return
> value.
> Focused on directory blocks, a NULL value returned from ext4_bread() means a
> hole, which cannot exist into a directory inode. It can pass undetected after a
> fix in an uninitialized error variable.
>
> The (now) initialized variable into ext4_getblk() may lead to a zero'ed return
> value of ext4_bread() to its callers, which can make the caller do not detect
> the hole in the directory inode.
>
> This checks for directory holes when buffer_head and error value are both
> zero'ed returning -EIO to their callers
>
> Some ext4_bread callers do not needed any changes either because they already
> had its own hole detector paths or because these are deprecaded (like
> dx_show_entries)
Note that in the "errors=continue" case, it is desirable to allow the Filesystem to continue even if a hole is found in the directory, at least for non-htree directories, since it is possible the the entry being looked up is in a different block.
> Signed-off-by: Carlos Maiolino <cmaiolino@...hat.com>
> ---
> fs/ext4/namei.c | 80 +++++++++++++++++++++++++++++++++++++++++++++++++--------
> 1 file changed, 69 insertions(+), 11 deletions(-)
>
> diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
> index 2a42cc0..1d5619b 100644
> --- a/fs/ext4/namei.c
> +++ b/fs/ext4/namei.c
> @@ -67,6 +67,11 @@ static struct buffer_head *ext4_append(handle_t *handle,
> bh = NULL;
> }
> }
> + if (!bh && !(*err)) {
> + *err = -EIO;
> + ext4_error(inode->i_sb, "Directory hole detected on inode %lu\n",
> + inode->i_ino);
> + }
> return bh;
> }
>
> @@ -696,8 +701,11 @@ dx_probe(const struct qstr *d_name, struct inode *dir,
> frame->entries = entries;
> frame->at = at;
> if (!indirect--) return frame;
> - if (!(bh = ext4_bread (NULL,dir, dx_get_block(at), 0, err)))
> + if (!(bh = ext4_bread (NULL,dir, dx_get_block(at), 0, err))) {
Please keep the original code style, do not Di the assignment inside the if() check. That is incorrect in several places in this patch.
> + if (!(*err))
> + *err = ERR_BAD_DX_DIR;
> goto fail2;
> + }
> at = entries = ((struct dx_node *) bh->b_data)->entries;
>
> if (!buffer_verified(bh) &&
> @@ -807,8 +815,15 @@ static int ext4_htree_next_block(struct inode *dir, __u32 hash,
> */
> while (num_frames--) {
> if (!(bh = ext4_bread(NULL, dir, dx_get_block(p->at),
> - 0, &err)))
> + 0, &err))) {
> + if (!err) {
> + ext4_error(dir->i_sb,
> + "Directory hole detected on inode %lu\n",
> + dir->i_ino);
> + return -EIO;
> + }
> return err; /* Failure */
> + }
>
> if (!buffer_verified(bh) &&
> !ext4_dx_csum_verify(dir,
> @@ -843,8 +858,14 @@ static int htree_dirblock_to_tree(struct file *dir_file,
>
> dxtrace(printk(KERN_INFO "In htree dirblock_to_tree: block %lu\n",
> (unsigned long)block));
> - if (!(bh = ext4_bread (NULL, dir, block, 0, &err)))
> + if (!(bh = ext4_bread (NULL, dir, block, 0, &err))) {
> + if (!err) {
> + err = -EIO;
> + ext4_error(dir->i_sb, "Directory hole detected on inode %lu\n",
> + dir->i_ino);
> + }
> return err;
> + }
>
> if (!buffer_verified(bh) &&
> !ext4_dirent_csum_verify(dir, (struct ext4_dir_entry *)bh->b_data))
> @@ -1267,8 +1288,15 @@ static struct buffer_head * ext4_dx_find_entry(struct inode *dir, const struct q
> return NULL;
> do {
> block = dx_get_block(frame->at);
> - if (!(bh = ext4_bread(NULL, dir, block, 0, err)))
> + if (!(bh = ext4_bread(NULL, dir, block, 0, err))) {
> + if (!(*err)) {
> + *err = -EIO;
> + ext4_error(dir->i_sb,
> + "Directory hole detected on inode %lu\n",
> + dir->i_ino);
> + }
> goto errout;
> + }
>
> if (!buffer_verified(bh) &&
> !ext4_dirent_csum_verify(dir,
> @@ -1801,9 +1829,15 @@ static int ext4_add_entry(handle_t *handle, struct dentry *dentry,
> }
> blocks = dir->i_size >> sb->s_blocksize_bits;
> for (block = 0; block < blocks; block++) {
> - bh = ext4_bread(handle, dir, block, 0, &retval);
> - if(!bh)
> + if (!(bh = ext4_bread(handle, dir, block, 0, &retval))) {
> + if (!retval) {
> + retval = -EIO;
> + ext4_error(inode->i_sb,
> + "Directory hole detected on inode %lu\n",
> + inode->i_ino);
> + }
> return retval;
> + }
> if (!buffer_verified(bh) &&
> !ext4_dirent_csum_verify(dir,
> (struct ext4_dir_entry *)bh->b_data))
> @@ -1860,8 +1894,15 @@ static int ext4_dx_add_entry(handle_t *handle, struct dentry *dentry,
> entries = frame->entries;
> at = frame->at;
>
> - if (!(bh = ext4_bread(handle,dir, dx_get_block(frame->at), 0, &err)))
> + if (!(bh = ext4_bread(handle,dir, dx_get_block(frame->at), 0, &err))) {
> + if (!err) {
> + err = -EIO;
> + ext4_error(dir->i_sb,
> + "Directory hole detected on inode %lu\n",
> + dir->i_ino);
> + }
> goto cleanup;
> + }
>
> if (!buffer_verified(bh) &&
> !ext4_dirent_csum_verify(dir, (struct ext4_dir_entry *)bh->b_data))
> @@ -2199,9 +2240,15 @@ retry:
> inode->i_op = &ext4_dir_inode_operations;
> inode->i_fop = &ext4_dir_operations;
> inode->i_size = EXT4_I(inode)->i_disksize = inode->i_sb->s_blocksize;
> - dir_block = ext4_bread(handle, inode, 0, 1, &err);
> - if (!dir_block)
> + if (!(dir_block = ext4_bread(handle, inode, 0, 1, &err))) {
> + if (!err) {
> + err = -EIO;
> + ext4_error(inode->i_sb,
> + "Directory hole detected on inode %lu\n",
> + inode->i_ino);
> + }
> goto out_clear_inode;
> + }
> BUFFER_TRACE(dir_block, "get_write_access");
> err = ext4_journal_get_write_access(handle, dir_block);
> if (err)
> @@ -2318,6 +2365,11 @@ static int empty_dir(struct inode *inode)
> EXT4_ERROR_INODE(inode,
> "error %d reading directory "
> "lblock %u", err, lblock);
> + else
> + ext4_warning(inode->i_sb,
> + "bad directory (dir #%lu) - no data block",
> + inode->i_ino);
> +
> offset += sb->s_blocksize;
> continue;
> }
> @@ -2826,9 +2878,15 @@ static int ext4_rename(struct inode *old_dir, struct dentry *old_dentry,
> goto end_rename;
> }
> retval = -EIO;
> - dir_bh = ext4_bread(handle, old_inode, 0, 0, &retval);
> - if (!dir_bh)
> + if(!(dir_bh = ext4_bread(handle, old_inode, 0, 0, &retval))) {
> + if (!retval) {
> + retval = -EIO;
> + ext4_error(old_inode->i_sb,
> + "Directory hole detected on inode %lu\n",
> + old_inode->i_ino);
> + }
> goto end_rename;
> + }
> if (!buffer_verified(dir_bh) &&
> !ext4_dirent_csum_verify(old_inode,
> (struct ext4_dir_entry *)dir_bh->b_data))
> --
> 1.7.11.4
>
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