[PATCH 1/2] ext4: check if directory block is within i_size

[PATCH 1/2] ext4: check if directory block is within i_size

[Lukas Czerner]

Currently ext4 directory handling code implicitly assumes that the
directory blocks are always within the i_size. In fact ext4_append()
will attempt to allocate next directory block based solely on i_size and
the i_size is then appropriately increased after a successful
allocation.

However, for this to work it requires i_size to be correct. If, for any
reason, the directory inode i_size is corrupted in a way that the
directory tree refers to a valid directory block past i_size, we could
end up corrupting parts of the directory tree structure by overwriting
already used directory blocks when modifying the directory.

Fix it by catching the corruption early in __ext4_read_dirblock().

Signed-off-by: Lukas Czerner <lczerner@redhat.com>
Addresses Red-Hat-Bugzilla: #2070205
Cc: stable@vger.kernel.org
---
 fs/ext4/namei.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index db4ba99d1ceb..cf460aa4f81d 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -110,6 +110,13 @@ static struct buffer_head *__ext4_read_dirblock(struct inode *inode,
 	struct ext4_dir_entry *dirent;
 	int is_dx_block = 0;
 
+	if (block >= inode->i_size) {
+		ext4_error_inode(inode, func, line, block,
+		       "Attempting to read directory block (%u) that is past i_size (%llu)",
+		       block, inode->i_size);
+		return ERR_PTR(-EFSCORRUPTED);
+	}
+
 	if (ext4_simulate_fail(inode->i_sb, EXT4_SIM_DIRBLOCK_EIO))
 		bh = ERR_PTR(-EIO);
 	else
-- 
2.35.3

[PATCH 2/2] ext4: make sure ext4_append() always allocates new block

[Lukas Czerner]

ext4_append() must always allocate a new block, otherwise we run the
risk of overwriting existing directory block corrupting the directory
tree in the process resulting in all manner of problems later on.

Add a sanity check to see if the logical block is already allocated and
error out if it is.

Signed-off-by: Lukas Czerner <lczerner@redhat.com>
---
 fs/ext4/namei.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index cf460aa4f81d..4af441494e09 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -54,6 +54,7 @@ static struct buffer_head *ext4_append(handle_t *handle,
 					struct inode *inode,
 					ext4_lblk_t *block)
 {
+	struct ext4_map_blocks map;
 	struct buffer_head *bh;
 	int err;
 
@@ -63,6 +64,21 @@ static struct buffer_head *ext4_append(handle_t *handle,
 		return ERR_PTR(-ENOSPC);
 
 	*block = inode->i_size >> inode->i_sb->s_blocksize_bits;
+	map.m_lblk = *block;
+	map.m_len = 1;
+
+	/*
+	 * We're appending new directory block. Make sure the block is not
+	 * allocated yet, otherwise we will end up corrupting the
+	 * directory.
+	 */
+	err = ext4_map_blocks(NULL, inode, &map, 0);
+	if (err < 0)
+		return ERR_PTR(err);
+	if (err) {
+		EXT4_ERROR_INODE(inode, "Logical block already allocated");
+		return ERR_PTR(-EFSCORRUPTED);
+	}
 
 	bh = ext4_bread(handle, inode, *block, EXT4_GET_BLOCKS_CREATE);
 	if (IS_ERR(bh))
-- 
2.35.3

Re: [PATCH 1/2] ext4: check if directory block is within i_size

[Andreas Dilger]

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On Jul 4, 2022, at 8:27 AM, Lukas Czerner <lczerner@redhat.com> wrote:
> 
> Currently ext4 directory handling code implicitly assumes that the
> directory blocks are always within the i_size. In fact ext4_append()
> will attempt to allocate next directory block based solely on i_size and
> the i_size is then appropriately increased after a successful
> allocation.
> 
> However, for this to work it requires i_size to be correct. If, for any
> reason, the directory inode i_size is corrupted in a way that the
> directory tree refers to a valid directory block past i_size, we could
> end up corrupting parts of the directory tree structure by overwriting
> already used directory blocks when modifying the directory.
> 
> Fix it by catching the corruption early in __ext4_read_dirblock().
> 
> Signed-off-by: Lukas Czerner <lczerner@redhat.com>

Reviewed-by: Andreas Dilger <adilger@dilger.ca>

> Addresses Red-Hat-Bugzilla: #2070205
> Cc: stable@vger.kernel.org
> ---
> fs/ext4/namei.c | 7 +++++++
> 1 file changed, 7 insertions(+)
> 
> diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
> index db4ba99d1ceb..cf460aa4f81d 100644
> --- a/fs/ext4/namei.c
> +++ b/fs/ext4/namei.c
> @@ -110,6 +110,13 @@ static struct buffer_head *__ext4_read_dirblock(struct inode *inode,
> 	struct ext4_dir_entry *dirent;
> 	int is_dx_block = 0;
> 
> +	if (block >= inode->i_size) {
> +		ext4_error_inode(inode, func, line, block,
> +		       "Attempting to read directory block (%u) that is past i_size (%llu)",
> +		       block, inode->i_size);
> +		return ERR_PTR(-EFSCORRUPTED);
> +	}
> +
> 	if (ext4_simulate_fail(inode->i_sb, EXT4_SIM_DIRBLOCK_EIO))
> 		bh = ERR_PTR(-EIO);
> 	else
> --
> 2.35.3
> 


Cheers, Andreas






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Re: [PATCH 2/2] ext4: make sure ext4_append() always allocates new block

[Andreas Dilger]

[-- Attachment #1: Type: text/plain, Size: 1650 bytes --]

On Jul 4, 2022, at 8:27 AM, Lukas Czerner <lczerner@redhat.com> wrote:
> 
> ext4_append() must always allocate a new block, otherwise we run the
> risk of overwriting existing directory block corrupting the directory
> tree in the process resulting in all manner of problems later on.
> 
> Add a sanity check to see if the logical block is already allocated and
> error out if it is.
> 
> Signed-off-by: Lukas Czerner <lczerner@redhat.com>

Reviewed-by: Andreas Dilger <adilger@dilger.ca>

> ---
> fs/ext4/namei.c | 16 ++++++++++++++++
> 1 file changed, 16 insertions(+)
> 
> diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
> index cf460aa4f81d..4af441494e09 100644
> --- a/fs/ext4/namei.c
> +++ b/fs/ext4/namei.c
> @@ -54,6 +54,7 @@ static struct buffer_head *ext4_append(handle_t *handle,
> 					struct inode *inode,
> 					ext4_lblk_t *block)
> {
> +	struct ext4_map_blocks map;
> 	struct buffer_head *bh;
> 	int err;
> 
> @@ -63,6 +64,21 @@ static struct buffer_head *ext4_append(handle_t *handle,
> 		return ERR_PTR(-ENOSPC);
> 
> 	*block = inode->i_size >> inode->i_sb->s_blocksize_bits;
> +	map.m_lblk = *block;
> +	map.m_len = 1;
> +
> +	/*
> +	 * We're appending new directory block. Make sure the block is not
> +	 * allocated yet, otherwise we will end up corrupting the
> +	 * directory.
> +	 */
> +	err = ext4_map_blocks(NULL, inode, &map, 0);
> +	if (err < 0)
> +		return ERR_PTR(err);
> +	if (err) {
> +		EXT4_ERROR_INODE(inode, "Logical block already allocated");
> +		return ERR_PTR(-EFSCORRUPTED);
> +	}
> 
> 	bh = ext4_bread(handle, inode, *block, EXT4_GET_BLOCKS_CREATE);
> 	if (IS_ERR(bh))
> --
> 2.35.3
> 


Cheers, Andreas






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Re: [PATCH 1/2] ext4: check if directory block is within i_size

[Theodore Ts'o]

On Mon, 4 Jul 2022 16:27:20 +0200, Lukas Czerner wrote:
> Currently ext4 directory handling code implicitly assumes that the
> directory blocks are always within the i_size. In fact ext4_append()
> will attempt to allocate next directory block based solely on i_size and
> the i_size is then appropriately increased after a successful
> allocation.
> 
> However, for this to work it requires i_size to be correct. If, for any
> reason, the directory inode i_size is corrupted in a way that the
> directory tree refers to a valid directory block past i_size, we could
> end up corrupting parts of the directory tree structure by overwriting
> already used directory blocks when modifying the directory.
> 
> [...]

Applied, thanks!

[1/2] ext4: check if directory block is within i_size
      commit: 65d23bd6e76ae07cee50c24d1fbeea4044aa41e7
[2/2] ext4: make sure ext4_append() always allocates new block
      commit: 6d3ab9450ea5ec08882ab2f255827f1a39e300de

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