Patchwork [dpdk-dev] test: fix sprintf with snprintf

login
register
mail settings
Submitter Aaron Conole
Date Feb. 8, 2019, 5:04 p.m.
Message ID <f7th8defbzd.fsf@dhcp-25.97.bos.redhat.com>
Download mbox | patch
Permalink /patch/721753/
State New
Headers show

Comments

Aaron Conole - Feb. 8, 2019, 5:04 p.m.
Pallantla Poornima <pallantlax.poornima@intel.com> writes:

> sprintf function is not secure as it doesn't check the length of string.
> More secure function snprintf is used.
>
> Fixes: 727909c592 ("app/test: introduce dynamic commands list")
> Cc: stable@dpdk.org
>
> Signed-off-by: Pallantla Poornima <pallantlax.poornima@intel.com>
> ---
>  test/test/commands.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/test/test/commands.c b/test/test/commands.c
> index 94fbc310e..5aeb35498 100644
> --- a/test/test/commands.c
> +++ b/test/test/commands.c
> @@ -367,6 +367,8 @@ int commands_init(void)
>  	struct test_command *t;
>  	char *commands, *ptr;
>  	int commands_len = 0;
> +	int total_written = 0;
> +	int count = 0;
>  
>  	TAILQ_FOREACH(t, &commands_list, next) {
>  		commands_len += strlen(t->command) + 1;
> @@ -378,7 +380,10 @@ int commands_init(void)
>  
>  	ptr = commands;
>  	TAILQ_FOREACH(t, &commands_list, next) {
> -		ptr += sprintf(ptr, "%s#", t->command);
> +		count = snprintf(ptr, commands_len - total_written - 1, "%s#",
> +				t->command);
> +		ptr += count;

This code is wrong.  From the manpage:

        Upon successful completion, the snprintf() function shall return
        the number of bytes that would be written to s had n been
        sufficiently large excluding the terminating null byte.

This code you've placed will improperly increment the number of bytes
taken, since you don't actually check it.

Additionally, the correct size is calculated in the preceeding blocks,
and then the appropriately sized block is allocated.  It doesn't make
any sense to make the change this way.

If you are intent on changing this code, I suggest something like the
following (completely untested code).  The rte_xsprintf() function can
be used in other areas where you're proposing these refactors (but again
see my earlier comments about whether these are actual concerns, or just
'I dislike the sprintf call').

---
---
Stephen Hemminger - Feb. 8, 2019, 5:35 p.m.
On Fri, 08 Feb 2019 12:04:22 -0500
Aaron Conole <aconole@redhat.com> wrote:

> Pallantla Poornima <pallantlax.poornima@intel.com> writes:
> 
> > sprintf function is not secure as it doesn't check the length of string.
> > More secure function snprintf is used.
> >
> > Fixes: 727909c592 ("app/test: introduce dynamic commands list")
> > Cc: stable@dpdk.org
> >
> > Signed-off-by: Pallantla Poornima <pallantlax.poornima@intel.com>
> > ---
> >  test/test/commands.c | 7 ++++++-
> >  1 file changed, 6 insertions(+), 1 deletion(-)
> >
> > diff --git a/test/test/commands.c b/test/test/commands.c
> > index 94fbc310e..5aeb35498 100644
> > --- a/test/test/commands.c
> > +++ b/test/test/commands.c
> > @@ -367,6 +367,8 @@ int commands_init(void)
> >  	struct test_command *t;
> >  	char *commands, *ptr;
> >  	int commands_len = 0;
> > +	int total_written = 0;
> > +	int count = 0;
> >  
> >  	TAILQ_FOREACH(t, &commands_list, next) {
> >  		commands_len += strlen(t->command) + 1;
> > @@ -378,7 +380,10 @@ int commands_init(void)
> >  
> >  	ptr = commands;
> >  	TAILQ_FOREACH(t, &commands_list, next) {
> > -		ptr += sprintf(ptr, "%s#", t->command);
> > +		count = snprintf(ptr, commands_len - total_written - 1, "%s#",
> > +				t->command);
> > +		ptr += count;  
> 
> This code is wrong.  From the manpage:
> 
>         Upon successful completion, the snprintf() function shall return
>         the number of bytes that would be written to s had n been
>         sufficiently large excluding the terminating null byte.
> 
> This code you've placed will improperly increment the number of bytes
> taken, since you don't actually check it.
> 
> Additionally, the correct size is calculated in the preceeding blocks,
> and then the appropriately sized block is allocated.  It doesn't make
> any sense to make the change this way.
> 
> If you are intent on changing this code, I suggest something like the
> following (completely untested code).  The rte_xsprintf() function can
> be used in other areas where you're proposing these refactors (but again
> see my earlier comments about whether these are actual concerns, or just
> 'I dislike the sprintf call').

I agree snprintf is dangerous.
Inventing another routine is not really helping much.
New code for printing should not be inline (because it isn't performance critical).

Why not just rewrite the code in the test to use better string management

Patch

diff --git a/lib/librte_eal/common/include/rte_string_fns.h b/lib/librte_eal/common/include/rte_string_fns.h
index 9a2a1ff90..3554c496a 100644
--- a/lib/librte_eal/common/include/rte_string_fns.h
+++ b/lib/librte_eal/common/include/rte_string_fns.h
@@ -98,6 +98,41 @@  rte_strlcpy(char *dst, const char *src, size_t size)
 ssize_t
 rte_strscpy(char *dst, const char *src, size_t dsize);
 
+/* Find a better place for this? */
+#define ALWAYS_ASSERT(expr) \
+	if (!(expr)) rte_panic("Assert failed: %s", #expr)
+
+/**
+ * Allocates an appropriately sized string and fills it with
+ * formatted output.  Aborts if no memory can be allocated.
+ *
+ * @param fmt
+ *   The format string.  See the documentation for printf
+ *   for valid format strings.
+ *
+ * @return
+ *   A string filled with formatted output.  Caller must release
+ *   this memory with a call to free().
+ */
+static inline char *
+rte_xsprintf(const char *fmt, ...)
+{
+	va_list args,args2;
+	size_t needed;
+	char *result;
+
+	va_start(args, fmt);
+	va_copy(args2, args);
+	needed = vsnprintf(NULL, 0, fmt, args);
+	result = malloc(needed+1);
+	ALWAYS_ASSERT(result != NULL);
+	vsnprintf(result, needed+1, fmt, args2);
+	va_end(args2);
+	va_end(args);
+
+	return result;
+}
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/test/test/commands.c b/test/test/commands.c
index 94fbc310e..eba96b9c9 100644
--- a/test/test/commands.c
+++ b/test/test/commands.c
@@ -365,24 +365,19 @@  cmdline_parse_ctx_t main_ctx[] = {
 int commands_init(void)
 {
 	struct test_command *t;
-	char *commands, *ptr;
-	int commands_len = 0;
+	char *ptr = NULL, *old;
 
 	TAILQ_FOREACH(t, &commands_list, next) {
-		commands_len += strlen(t->command) + 1;
-	}
-
-	commands = malloc(commands_len + 1);
-	if (!commands)
-		return -1;
+		if (!ptr) {
+			ptr = xprintf("%s", t->command);
+			continue;
+		}
 
-	ptr = commands;
-	TAILQ_FOREACH(t, &commands_list, next) {
-		ptr += sprintf(ptr, "%s#", t->command);
+		old = ptr;
+		ptr = xprintf("%s#%s", old, t->command);
+		free(old);
 	}
-	ptr--;
-	ptr[0] = '\0';
 
-	cmd_autotest_autotest.string_data.str = commands;
+	cmd_autotest_autotest.string_data.str = ptr;
 	return 0;
 }