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kernfs: Convert kernfs_name_locked() from strlcpy() to strscpy()

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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 <gregkh@linuxfoundation.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Azeem Shaikh <azeemshaikh38@gmail.com>
Link: https://lore.kernel.org/r/20231116192127.1558276-2-keescook@chromium.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20231212211741.164376-2-keescook@chromium.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Kees Cook 2023-12-12 13:17:39 -08:00 committed by Greg Kroah-Hartman
parent 792e04768e
commit 5b56bf5cdb
1 changed files with 5 additions and 5 deletions
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10
fs/kernfs/dir.c
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@ -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.
*/