| Message ID | 20230830160410.3820390-1-azeemshaikh38@gmail.com |
|---|---|
| State | New |
| Headers | show |
| Series | vt: Fix potential read overflow of kernel memory | expand |
On Wed, Aug 30, 2023 at 04:04:10PM +0000, Azeem Shaikh wrote: > strlcpy() reads the entire source buffer first. > This read may exceed the destination size limit if > a source string is not NUL-terminated [1]. But that's not the case here, right? So your "potential read overflow" isn't relevant here. > The copy_to_user() call uses @len returned from strlcpy() directly > without checking its value. This could potentially lead to read > overflow. But can it? How? Those are all hard-coded strings, in the kernel source, there is no potential overflow here. And you know the buffer size is correct as well. So why even check? > 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 <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 358f216c6cd6..15359c328a23 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 = -EFAULT; > + break; > + } Don't check for impossible things please. thanks, greg k-h
diff --git a/drivers/tty/vt/keyboard.c b/drivers/tty/vt/keyboard.c index 358f216c6cd6..15359c328a23 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 = -EFAULT; + break; + } ret = copy_to_user(user_kdgkb->kb_string, kbs, len + 1) ? -EFAULT : 0; - break; } case KDSKBSENT:
strlcpy() reads the entire source buffer first. This read may exceed the destination size limit if a source string is not NUL-terminated [1]. The copy_to_user() call uses @len returned from strlcpy() directly without checking its value. This could potentially lead to read overflow. 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 <azeemshaikh38@gmail.com> --- drivers/tty/vt/keyboard.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) -- 2.42.0.rc2.253.gd59a3bf2b4-goog