linux-hardening - [PATCH v2] vt: Replace strlcpy with strscpy

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Date:   Tue, 19 Sep 2023 19:21:56 +0000
From:   Azeem Shaikh <azeems@...gle.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>
Cc:     linux-hardening@...r.kernel.org, Azeem Shaikh <azeems@...gle.com>,
        linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org,
        Ard Biesheuvel <ardb@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Tony Luck <tony.luck@...el.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>
Subject: [PATCH v2] vt: Replace strlcpy with strscpy

strlcpy() reads the entire source buffer first and returns the size of
the source string, not the destination string, which can be accidentally
misused [1].

The copy_to_user() call uses @len returned from strlcpy() directly
without checking its value. This could potentially lead to read
overflow. There is no existing bug since @len is always guaranteed to be
greater than hardcoded strings in @func_table[kb_func]. But as written
it is very fragile and specifically uses a strlcpy() result without sanity
checking and using it to copy to userspace.

In an effort to remove strlcpy() completely [2], replace
strlcpy() here with strscpy().

[1] https://www.kernel.org/doc/html/latest/process/deprecated.html#strlcpy
[2] https://github.com/KSPP/linux/issues/89

Signed-off-by: Azeem Shaikh <azeems@...gle.com>
---
v2:
 * Return -ENOSPC instead of -EFAULT in case of truncation.
 * Update commit log to clarify that there is no exploitable bug but instead the code uses a fragile anti-pattern.

v1:
 * https://lore.kernel.org/all/20230830160410.3820390-1-azeemshaikh38@gmail.com/

 drivers/tty/vt/keyboard.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/vt/keyboard.c b/drivers/tty/vt/keyboard.c
index 1fe6107b539b..12a192e1196b 100644
--- a/drivers/tty/vt/keyboard.c
+++ b/drivers/tty/vt/keyboard.c
@@ -2079,12 +2079,15 @@ int vt_do_kdgkb_ioctl(int cmd, struct kbsentry __user *user_kdgkb, int perm)
 			return -ENOMEM;

 		spin_lock_irqsave(&func_buf_lock, flags);
-		len = strlcpy(kbs, func_table[kb_func] ? : "", len);
+		len = strscpy(kbs, func_table[kb_func] ? : "", len);
 		spin_unlock_irqrestore(&func_buf_lock, flags);

+		if (len < 0) {
+			ret = -ENOSPC;
+			break;
+		}
 		ret = copy_to_user(user_kdgkb->kb_string, kbs, len + 1) ?
 			-EFAULT : 0;
-
 		break;
 	}
 	case KDSKBSENT:
--
2.42.0.459.ge4e396fd5e-goog