[PATCH v2] vt: Replace strlcpy with strscpy
From: Azeem Shaikh
Date: Tue Sep 19 2023 - 15:22:17 EST
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@xxxxxxxxxx>
---
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@xxxxxxxxx/
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