[Xen-devel] [PATCH] console: avoid buffer overflow in guest_console_write()

[Jan Beulich <jbeulich@xxxxxxxx>]

The switch of guest_console_write()'s second parameter from plain to
unsigned int has caused the function's main loop header to no longer
guard the min_t() use within the function against effectively negative
values, due to the casts hidden inside the macro. Replace by a plain
min(), converting one of the arguments suitably without involving any
cast.

Fixes: ea601ec9995b ("xen/console: Rework HYPERCALL_console_io interface")
Reported-by: Ilja Van Sprundel <ivansprundel@xxxxxxxxxxxx>
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/drivers/char/console.c
+++ b/xen/drivers/char/console.c
@@ -538,7 +538,7 @@ static long guest_console_write(XEN_GUES
                 __HYPERVISOR_console_io, "iih",
                 CONSOLEIO_write, count, buffer);
 
-        kcount = min_t(int, count, sizeof(kbuf)-1);
+        kcount = min(count + sizeof(char[0]), sizeof(kbuf) - 1);
         if ( copy_from_guest(kbuf, buffer, kcount) )
             return -EFAULT;
 

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