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

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>

authored by

Kees Cook and committed by
Greg Kroah-Hartman 5b56bf5c 792e0476

+5 -5
+5 -5
fs/kernfs/dir.c
··· 54 54 static int kernfs_name_locked(struct kernfs_node *kn, char *buf, size_t buflen) 55 55 { 56 56 if (!kn) 57 - return strlcpy(buf, "(null)", buflen); 57 + return strscpy(buf, "(null)", buflen); 58 58 59 - return strlcpy(buf, kn->parent ? kn->name : "/", buflen); 59 + return strscpy(buf, kn->parent ? kn->name : "/", buflen); 60 60 } 61 61 62 62 /* kernfs_node_depth - compute depth from @from to @to */ ··· 182 182 * @buflen: size of @buf 183 183 * 184 184 * Copies the name of @kn into @buf of @buflen bytes. The behavior is 185 - * similar to strlcpy(). 185 + * similar to strscpy(). 186 186 * 187 187 * Fills buffer with "(null)" if @kn is %NULL. 188 188 * 189 - * Return: the length of @kn's name and if @buf isn't long enough, 190 - * it's filled up to @buflen-1 and nul terminated. 189 + * Return: the resulting length of @buf. If @buf isn't long enough, 190 + * it's filled up to @buflen-1 and nul terminated, and returns -E2BIG. 191 191 * 192 192 * This function can be called from any context. 193 193 */