[Xen-devel] [PATCH] tools: libxl: do not overrun input buffer in libxl__parse_mac

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

Valgrind reports:
==7971== Invalid read of size 1
==7971==    at 0x40877BE: libxl__parse_mac (libxl_internal.c:288)
==7971==    by 0x405C5F8: libxl__device_nic_from_xs_be (libxl.c:3405)
==7971==    by 0x4065542: libxl__append_nic_list_of_type (libxl.c:3484)
==7971==    by 0x4065542: libxl_device_nic_list (libxl.c:3504)
==7971==    by 0x406F561: libxl_retrieve_domain_configuration (libxl.c:6661)
==7971==    by 0x805671C: reload_domain_config (xl_cmdimpl.c:2037)
==7971==    by 0x8057F30: handle_domain_death (xl_cmdimpl.c:2116)
==7971==    by 0x8057F30: create_domain (xl_cmdimpl.c:2580)
==7971==    by 0x805B4B2: main_create (xl_cmdimpl.c:4652)
==7971==    by 0x804EAB2: main (xl.c:378)

This is because on the final iteration the tok += 3 skips over the terminating
NUL to the next byte, and then *tok reads it. Fix this by using endptr as the
iterator.

Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
---
 tools/libxl/libxl_internal.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/tools/libxl/libxl_internal.c b/tools/libxl/libxl_internal.c
index 02a71cb..00c3b1e 100644
--- a/tools/libxl/libxl_internal.c
+++ b/tools/libxl/libxl_internal.c
@@ -284,10 +284,12 @@ _hidden int libxl__parse_mac(const char *s, libxl_mac mac)
     char *endptr;
     int i;
 
-    for (i = 0, tok = s; *tok && (i < 6); ++i, tok += 3) {
+    for (i = 0, tok = s; *tok && (i < 6); ++i, tok = endptr) {
         mac[i] = strtol(tok, &endptr, 16);
         if (endptr != (tok + 2) || (*endptr != '\0' && *endptr != ':') )
             return ERROR_INVAL;
+        if (*endptr == ':')
+            endptr++;
     }
     if ( i != 6 )
         return ERROR_INVAL;
-- 
1.7.10.4


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