strlcpy() reads the entire source buffer first. This read may exceed
the destination size limit. This is both inefficient and can lead
to linear read overflows if a source string is not NUL-terminated[1].
Additionally, it returns the size of the source string, not the
resulting size of the destination string. In an effort to remove strlcpy()
completely[2], replace strlcpy() here with strscpy().
Nothing actually checks the return value coming from kernfs_name_locked(),
so this has no impact on error paths. The caller hierarchy is:
kernfs_name_locked()
kernfs_name()
pr_cont_kernfs_name()
return value ignored
cgroup_name()
current_css_set_cg_links_read()
return value ignored
print_page_owner_memcg()
return value ignored
Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strlcpy [1]
Link: https://github.com/KSPP/linux/issues/89 [2]
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: Azeem Shaikh <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Kees Cook <[email protected]>
---
fs/kernfs/dir.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)
diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index 37353901ede1..8c0e5442597e 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -54,9 +54,9 @@ static bool kernfs_lockdep(struct kernfs_node *kn)
static int kernfs_name_locked(struct kernfs_node *kn, char *buf, size_t buflen)
{
if (!kn)
- return strlcpy(buf, "(null)", buflen);
+ return strscpy(buf, "(null)", buflen);
- return strlcpy(buf, kn->parent ? kn->name : "/", buflen);
+ return strscpy(buf, kn->parent ? kn->name : "/", buflen);
}
/* kernfs_node_depth - compute depth from @from to @to */
@@ -182,12 +182,12 @@ static int kernfs_path_from_node_locked(struct kernfs_node *kn_to,
* @buflen: size of @buf
*
* Copies the name of @kn into @buf of @buflen bytes. The behavior is
- * similar to strlcpy().
+ * similar to strscpy().
*
* Fills buffer with "(null)" if @kn is %NULL.
*
- * Return: the length of @kn's name and if @buf isn't long enough,
- * it's filled up to @buflen-1 and nul terminated.
+ * Return: the resulting length of @buf. If @buf isn't long enough,
+ * it's filled up to @buflen-1 and nul terminated, and returns -E2BIG.
*
* This function can be called from any context.
*/
--
2.34.1
On Tue, Dec 12, 2023 at 01:17:39PM -0800, Kees Cook wrote:
> strlcpy() reads the entire source buffer first. This read may exceed
> the destination size limit. This is both inefficient and can lead
> to linear read overflows if a source string is not NUL-terminated[1].
> Additionally, it returns the size of the source string, not the
> resulting size of the destination string. In an effort to remove strlcpy()
> completely[2], replace strlcpy() here with strscpy().
>
> Nothing actually checks the return value coming from kernfs_name_locked(),
> so this has no impact on error paths. The caller hierarchy is:
>
> kernfs_name_locked()
> kernfs_name()
> pr_cont_kernfs_name()
> return value ignored
> cgroup_name()
> current_css_set_cg_links_read()
> return value ignored
> print_page_owner_memcg()
> return value ignored
>
> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strlcpy [1]
> Link: https://github.com/KSPP/linux/issues/89 [2]
> Cc: Greg Kroah-Hartman <[email protected]>
> Cc: Tejun Heo <[email protected]>
> Cc: Azeem Shaikh <[email protected]>
> Link: https://lore.kernel.org/r/[email protected]
> Signed-off-by: Kees Cook <[email protected]>
Acked-by: Tejun Heo <[email protected]>
Thanks.
--
tejun