[bpf PATCH] bpf: fix uninitialized variable in bpf tools

[bpf PATCH] bpf: fix uninitialized variable in bpf tools

[John Fastabend]

Here the variable cont is used as the saved_pointer for a call to
strtok_r(). It is safe to use the value uninitialized in this
context however and the later reference is only ever used if
the strtok_r is successful. But, 'gcc-5' at least doesn't have all
this knowledge so initialize cont to NULL. Additionally, do the
natural NULL check before accessing just for completness.

The warning is the following:

./bpf/tools/bpf/bpf_dbg.c: In function ‘cmd_load’:
./bpf/tools/bpf/bpf_dbg.c:1077:13: warning: ‘cont’ may be used uninitialized in this function [-Wmaybe-uninitialized]
  } else if (matches(subcmd, "pcap") == 0) {

Fixes: fd981e3c321a "filter: bpf_dbg: add minimal bpf debugger"
Signed-off-by: John Fastabend <john.fastabend@gmail.com>
---
 tools/bpf/bpf_dbg.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/tools/bpf/bpf_dbg.c b/tools/bpf/bpf_dbg.c
index 4f254bc..61b9aa5 100644
--- a/tools/bpf/bpf_dbg.c
+++ b/tools/bpf/bpf_dbg.c
@@ -1063,7 +1063,7 @@ static int cmd_load_pcap(char *file)
 
 static int cmd_load(char *arg)
 {
-	char *subcmd, *cont, *tmp = strdup(arg);
+	char *subcmd, *cont = NULL, *tmp = strdup(arg);
 	int ret = CMD_OK;
 
 	subcmd = strtok_r(tmp, " ", &cont);
@@ -1073,7 +1073,10 @@ static int cmd_load(char *arg)
 		bpf_reset();
 		bpf_reset_breakpoints();
 
-		ret = cmd_load_bpf(cont);
+		if (!cont)
+			ret = CMD_ERR;
+		else
+			ret = cmd_load_bpf(cont);
 	} else if (matches(subcmd, "pcap") == 0) {
 		ret = cmd_load_pcap(cont);
 	} else {

Re: [bpf PATCH] bpf: fix uninitialized variable in bpf tools

[Daniel Borkmann]

On 04/26/2018 12:08 AM, John Fastabend wrote:
> Here the variable cont is used as the saved_pointer for a call to
> strtok_r(). It is safe to use the value uninitialized in this
> context however and the later reference is only ever used if
> the strtok_r is successful. But, 'gcc-5' at least doesn't have all
> this knowledge so initialize cont to NULL. Additionally, do the
> natural NULL check before accessing just for completness.
> 
> The warning is the following:
> 
> ./bpf/tools/bpf/bpf_dbg.c: In function ‘cmd_load’:
> ./bpf/tools/bpf/bpf_dbg.c:1077:13: warning: ‘cont’ may be used uninitialized in this function [-Wmaybe-uninitialized]
>   } else if (matches(subcmd, "pcap") == 0) {
> 
> Fixes: fd981e3c321a "filter: bpf_dbg: add minimal bpf debugger"
> Signed-off-by: John Fastabend <john.fastabend@gmail.com>

Applied to bpf tree, thanks John!