[U-Boot] [RFC/PATCH] common/command.c: Guard strchr/strlen from NULL pointer

[Thomas Weber <weber@corscience.de>]

Guard strchr/strlen from being called with NULL pointer. 
This line is crashing on OMAP3/Devkit8000 when command "env" is called without subcommand.

Toolchain is Codesourcery 2010q1.

The cmd is NULL in this case because the calling function "do_env" decremented the argc 
without checking if there are still arguments available.

caller:
static int do_env (cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
...
        /* drop initial "env" arg */
        argc--;
        argv++;

        cp = find_cmd_tbl(argv[0], cmd_env_sub, ARRAY_SIZE(cmd_env_sub));


Signed-off-by: Thomas Weber <weber@corscience.de>
---
 common/command.c |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/common/command.c b/common/command.c
index 0020eac..03a713a 100644
--- a/common/command.c
+++ b/common/command.c
@@ -105,14 +105,15 @@ cmd_tbl_t *find_cmd_tbl (const char *cmd, cmd_tbl_t *table, int table_len)
 	cmd_tbl_t *cmdtp;
 	cmd_tbl_t *cmdtp_temp = table;	/*Init value */
 	const char *p;
-	int len;
+	int len = 0;
 	int n_found = 0;
 
 	/*
 	 * Some commands allow length modifiers (like "cp.b");
 	 * compare command name only until first dot.
 	 */
-	len = ((p = strchr(cmd, '.')) == NULL) ? strlen (cmd) : (p - cmd);
+	if (cmd != NULL)
+		len = ((p = strchr(cmd, '.')) == NULL) ? strlen (cmd) : (p - cmd);
 
 	for (cmdtp = table;
 	     cmdtp != table + table_len;
-- 
1.7.3.2