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b=H4sIAHmNA2UC/x3MPQqEQAxA4atIagP+jLrrVRYLmURNM0riiiLe3 dHmwde8E4xV2KBNTlDexGQOEXmagJ/6MDIKRUORFWX2zR3aqsEvB5LKxmo4CeH/icfe1dVQcvN xRBAHi/Ig+zv/ddd1A6Gwul9sAAAA X-Developer-Key: i=justinstitt@google.com; a=ed25519; pk=tC3hNkJQTpNX/gLKxTNQKDmiQl6QjBNCGKJINqAdJsE= X-Developer-Signature: v=1; a=ed25519-sha256; t=1694731644; l=2748; i=justinstitt@google.com; s=20230717; h=from:subject:message-id; bh=Ro3W2l30+BkUgaszKfSJpsko0I3zSOwBNarLcip1Cv0=; b=+Ja/3VwcQv8Olj4st1v7gaQMddtIhh5AF/TwEtWpW6owvTXLz0/I8erXLOUpXoFmb5Z9njm4T vZydOgdhr/SDE99w0xuyh/SH2rl1X/0la8SdmEemgGQah5zf2h7fMX+ X-Mailer: b4 0.12.3 Message-ID: <20230914-strncpy-drivers-hid-uhid-c-v1-1-18a190060d8d@google.com> Subject: [PATCH] HID: uhid: refactor deprecated strncpy From: Justin Stitt To: David Rheinsberg , Jiri Kosina , Benjamin Tissoires Cc: linux-input@vger.kernel.org, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org, Kees Cook , Justin Stitt Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-Greylist: Sender passed SPF test, not delayed by milter-greylist-4.6.4 (morse.vger.email [0.0.0.0]); Thu, 14 Sep 2023 15:47:35 -0700 (PDT) X-Spam-Status: No, score=-8.4 required=5.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_IN_DEF_DKIM_WL autolearn=unavailable autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on morse.vger.email X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: 1777073454630333187 X-GMAIL-MSGID: 1777073454630333187 `strncpy` is deprecated for use on NUL-terminated destination strings [1]. We should prefer more robust and less ambiguous string interfaces. A suitable replacement is `strscpy` [2] due to the fact that it guarantees NUL-termination on the destination buffer without unnecessarily NUL-padding. Looking at: Commit 4d26d1d1e806 ("Revert "HID: uhid: use strlcpy() instead of strncpy()"") we see referenced the fact that many attempts have been made to change these strncpy's into strlcpy to no success. I think strscpy is an objectively better interface here as it doesn't unnecessarily NUL-pad the destination buffer whilst allowing us to drop the `len = min(...)` pattern as strscpy will implicitly limit the number of bytes copied by the smaller of its dest and src arguments. So while the existing code may not have a bug (i.e: overread problems) we should still favor strscpy due to readability (plus a very slight performance boost). Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1] Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2] Link: https://github.com/KSPP/linux/issues/90 Cc: linux-hardening@vger.kernel.org Cc: Kees Cook Signed-off-by: Justin Stitt Reviewed-by: Kees Cook --- drivers/hid/uhid.c | 12 ++++-------- 1 file changed, 4 insertions(+), 8 deletions(-) --- base-commit: 3669558bdf354cd352be955ef2764cde6a9bf5ec change-id: 20230914-strncpy-drivers-hid-uhid-c-a465f3e784dd Best regards, -- Justin Stitt diff --git a/drivers/hid/uhid.c b/drivers/hid/uhid.c index 4588d2cd4ea4..00e1566ad37b 100644 --- a/drivers/hid/uhid.c +++ b/drivers/hid/uhid.c @@ -490,7 +490,7 @@ static int uhid_dev_create2(struct uhid_device *uhid, const struct uhid_event *ev) { struct hid_device *hid; - size_t rd_size, len; + size_t rd_size; void *rd_data; int ret; @@ -514,13 +514,9 @@ static int uhid_dev_create2(struct uhid_device *uhid, goto err_free; } - /* @hid is zero-initialized, strncpy() is correct, strlcpy() not */ - len = min(sizeof(hid->name), sizeof(ev->u.create2.name)) - 1; - strncpy(hid->name, ev->u.create2.name, len); - len = min(sizeof(hid->phys), sizeof(ev->u.create2.phys)) - 1; - strncpy(hid->phys, ev->u.create2.phys, len); - len = min(sizeof(hid->uniq), sizeof(ev->u.create2.uniq)) - 1; - strncpy(hid->uniq, ev->u.create2.uniq, len); + strscpy(hid->name, ev->u.create2.name, sizeof(hid->name)); + strscpy(hid->phys, ev->u.create2.phys, sizeof(hid->phys)); + strscpy(hid->uniq, ev->u.create2.uniq, sizeof(hid->uniq)); hid->ll_driver = &uhid_hid_driver; hid->bus = ev->u.create2.bus;