[PATCH] Squashfs: remove deprecated strncpy by not copying the string

[PATCH] Squashfs: remove deprecated strncpy by not copying the string

[Phillip Lougher]

Squashfs copied the passed string (name) into a temporary buffer
to ensure it was NUL-terminated.  This however is completely
unnecessary as the string is already NUL-terminated.  So remove
the deprecated strncpy() by completely removing the string copy.

The background behind this unnecessary string copy is that it
dates back to the days when Squashfs was an out of kernel patch.
The code deliberately did not assume the string was NUL-terminated
in case in future this changed (due to kernel changes).  This
would mean the out of tree patches would be broken but still
compile OK.

Signed-off-by: Phillip Lougher <phillip@squashfs.org.uk>
---
 fs/squashfs/namei.c | 14 ++++----------
 1 file changed, 4 insertions(+), 10 deletions(-)

diff --git a/fs/squashfs/namei.c b/fs/squashfs/namei.c
index 11e4539b9eae..65aae7e2a859 100644
--- a/fs/squashfs/namei.c
+++ b/fs/squashfs/namei.c
@@ -62,27 +62,21 @@
  */
 static int get_dir_index_using_name(struct super_block *sb,
 			u64 *next_block, int *next_offset, u64 index_start,
-			int index_offset, int i_count, const char *name,
-			int len)
+			int index_offset, int i_count, const char *name)
 {
 	struct squashfs_sb_info *msblk = sb->s_fs_info;
 	int i, length = 0, err;
 	unsigned int size;
 	struct squashfs_dir_index *index;
-	char *str;
 
 	TRACE("Entered get_dir_index_using_name, i_count %d\n", i_count);
 
-	index = kmalloc(sizeof(*index) + SQUASHFS_NAME_LEN * 2 + 2, GFP_KERNEL);
+	index = kmalloc(sizeof(*index) + SQUASHFS_NAME_LEN + 1, GFP_KERNEL);
 	if (index == NULL) {
 		ERROR("Failed to allocate squashfs_dir_index\n");
 		goto out;
 	}
 
-	str = &index->name[SQUASHFS_NAME_LEN + 1];
-	strncpy(str, name, len);
-	str[len] = '\0';
-
 	for (i = 0; i < i_count; i++) {
 		err = squashfs_read_metadata(sb, index, &index_start,
 					&index_offset, sizeof(*index));
@@ -101,7 +95,7 @@ static int get_dir_index_using_name(struct super_block *sb,
 
 		index->name[size] = '\0';
 
-		if (strcmp(index->name, str) > 0)
+		if (strcmp(index->name, name) > 0)
 			break;
 
 		length = le32_to_cpu(index->index);
@@ -153,7 +147,7 @@ static struct dentry *squashfs_lookup(struct inode *dir, struct dentry *dentry,
 	length = get_dir_index_using_name(dir->i_sb, &block, &offset,
 				squashfs_i(dir)->dir_idx_start,
 				squashfs_i(dir)->dir_idx_offset,
-				squashfs_i(dir)->dir_idx_cnt, name, len);
+				squashfs_i(dir)->dir_idx_cnt, name);
 
 	while (length < i_size_read(dir)) {
 		/*
-- 
2.39.2

Re: [PATCH] Squashfs: remove deprecated strncpy by not copying the string

[Kees Cook]

On Wed, Apr 03, 2024 at 07:33:52PM +0100, Phillip Lougher wrote:
> Squashfs copied the passed string (name) into a temporary buffer
> to ensure it was NUL-terminated.  This however is completely
> unnecessary as the string is already NUL-terminated.  So remove
> the deprecated strncpy() by completely removing the string copy.
> 
> The background behind this unnecessary string copy is that it
> dates back to the days when Squashfs was an out of kernel patch.
> The code deliberately did not assume the string was NUL-terminated
> in case in future this changed (due to kernel changes).  This
> would mean the out of tree patches would be broken but still
> compile OK.
> 
> Signed-off-by: Phillip Lougher <phillip@squashfs.org.uk>

Thanks!

Reviewed-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook

Re: [PATCH] Squashfs: remove deprecated strncpy by not copying the string

[Justin Stitt]

On Wed, Apr 3, 2024 at 11:34 AM Phillip Lougher <phillip@squashfs.org.uk> wrote:
>
> Squashfs copied the passed string (name) into a temporary buffer
> to ensure it was NUL-terminated.  This however is completely
> unnecessary as the string is already NUL-terminated.  So remove
> the deprecated strncpy() by completely removing the string copy.
>
> The background behind this unnecessary string copy is that it
> dates back to the days when Squashfs was an out of kernel patch.
> The code deliberately did not assume the string was NUL-terminated
> in case in future this changed (due to kernel changes).  This
> would mean the out of tree patches would be broken but still
> compile OK.
>
> Signed-off-by: Phillip Lougher <phillip@squashfs.org.uk>

Reviewed-by: Justin Stitt <justinstitt@google.com>

> ---
>  fs/squashfs/namei.c | 14 ++++----------
>  1 file changed, 4 insertions(+), 10 deletions(-)
>
> diff --git a/fs/squashfs/namei.c b/fs/squashfs/namei.c
> index 11e4539b9eae..65aae7e2a859 100644
> --- a/fs/squashfs/namei.c
> +++ b/fs/squashfs/namei.c
> @@ -62,27 +62,21 @@
>   */
>  static int get_dir_index_using_name(struct super_block *sb,
>                         u64 *next_block, int *next_offset, u64 index_start,
> -                       int index_offset, int i_count, const char *name,
> -                       int len)
> +                       int index_offset, int i_count, const char *name)
>  {
>         struct squashfs_sb_info *msblk = sb->s_fs_info;
>         int i, length = 0, err;
>         unsigned int size;
>         struct squashfs_dir_index *index;
> -       char *str;
>
>         TRACE("Entered get_dir_index_using_name, i_count %d\n", i_count);
>
> -       index = kmalloc(sizeof(*index) + SQUASHFS_NAME_LEN * 2 + 2, GFP_KERNEL);
> +       index = kmalloc(sizeof(*index) + SQUASHFS_NAME_LEN + 1, GFP_KERNEL);
>         if (index == NULL) {
>                 ERROR("Failed to allocate squashfs_dir_index\n");
>                 goto out;
>         }
>
> -       str = &index->name[SQUASHFS_NAME_LEN + 1];
> -       strncpy(str, name, len);
> -       str[len] = '\0';
> -
>         for (i = 0; i < i_count; i++) {
>                 err = squashfs_read_metadata(sb, index, &index_start,
>                                         &index_offset, sizeof(*index));
> @@ -101,7 +95,7 @@ static int get_dir_index_using_name(struct super_block *sb,
>
>                 index->name[size] = '\0';
>
> -               if (strcmp(index->name, str) > 0)
> +               if (strcmp(index->name, name) > 0)
>                         break;
>
>                 length = le32_to_cpu(index->index);
> @@ -153,7 +147,7 @@ static struct dentry *squashfs_lookup(struct inode *dir, struct dentry *dentry,
>         length = get_dir_index_using_name(dir->i_sb, &block, &offset,
>                                 squashfs_i(dir)->dir_idx_start,
>                                 squashfs_i(dir)->dir_idx_offset,
> -                               squashfs_i(dir)->dir_idx_cnt, name, len);
> +                               squashfs_i(dir)->dir_idx_cnt, name);
>
>         while (length < i_size_read(dir)) {
>                 /*
> --
> 2.39.2
>