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[PATCH] tty: vt: keyboard: add range check to kbs->kb_func index

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  [PATCH] tty: vt: keyboard: add range check to kbs->kb_func index Colin King <colin.king@canonical.com> - 2017-09-20 23:40 +0200
    Re: [PATCH] tty: vt: keyboard: add range check to kbs->kb_func index Dan Carpenter <dan.carpenter@oracle.com> - 2017-09-21 01:50 +0200

#1736178 — [PATCH] tty: vt: keyboard: add range check to kbs->kb_func index

From: Colin Ian King <colin.king@canonical.com>

A value outside the range 0..MAX_NR_FUNC-1 in kbs->kb_func will
cause an array bounds overflow on func_table. Fix this by adding
a range check.

Detected by CoverityScan, CID#401961 ("Untrusted array index read")

Fixes: 079c9534a96d ("vt:tackle kbd_table")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
---
 drivers/tty/vt/keyboard.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/tty/vt/keyboard.c b/drivers/tty/vt/keyboard.c
index f4166263bb3a..1ecf545a96a8 100644
--- a/drivers/tty/vt/keyboard.c
+++ b/drivers/tty/vt/keyboard.c
@@ -1982,6 +1982,11 @@ int vt_do_kdgkb_ioctl(int cmd, struct kbsentry __user *user_kdgkb, int perm)
 	kbs->kb_string[sizeof(kbs->kb_string)-1] = '\0';
 	i = kbs->kb_func;
 
+	if (i < 0 || i >= MAX_NR_FUNC) {
+		ret = -EINVAL;
+		goto reterr;
+	}
+
 	switch (cmd) {
 	case KDGKBSENT:
 		sz = sizeof(kbs->kb_string) - 1; /* sz should have been
-- 
2.14.1

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#1736265

On Wed, Sep 20, 2017 at 10:38:28PM +0100, Colin King wrote:
> From: Colin Ian King <colin.king@canonical.com>
> 
> A value outside the range 0..MAX_NR_FUNC-1 in kbs->kb_func will
> cause an array bounds overflow on func_table. Fix this by adding
> a range check.
> 
> Detected by CoverityScan, CID#401961 ("Untrusted array index read")
> 
> Fixes: 079c9534a96d ("vt:tackle kbd_table")
> Signed-off-by: Colin Ian King <colin.king@canonical.com>
> ---
>  drivers/tty/vt/keyboard.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/tty/vt/keyboard.c b/drivers/tty/vt/keyboard.c
> index f4166263bb3a..1ecf545a96a8 100644
> --- a/drivers/tty/vt/keyboard.c
> +++ b/drivers/tty/vt/keyboard.c
> @@ -1982,6 +1982,11 @@ int vt_do_kdgkb_ioctl(int cmd, struct kbsentry __user *user_kdgkb, int perm)
>  	kbs->kb_string[sizeof(kbs->kb_string)-1] = '\0';
>  	i = kbs->kb_func;
>  
> +	if (i < 0 || i >= MAX_NR_FUNC) {

kbs->kb_func is an unsigned char and MAX_NR_FUNC is 256 so this check
will never be true.

regards,
dan carpenter

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