Hi Uwe,
Thanks for the review, very appreciated.
On Mon, 6 Nov 2017 13:04:26 +0100, Uwe Kleine-König wrote:
> Hello Jean,
>
> On Tue, Oct 31, 2017 at 08:16:04AM +0100, Jean Delvare wrote:
> > sprintf isn't safe, use snprintf instead.
> > ---
> > tools/i2cbusses.c | 10 +++++-----
> > 1 file changed, 5 insertions(+), 5 deletions(-)
> >
> > --- a/tools/i2cbusses.c
> > +++ b/tools/i2cbusses.c
> > @@ -220,18 +220,18 @@ struct i2c_adap *gather_i2c_busses(void)
> >
> > /* this should work for kernels 2.6.5 or higher and */
> > /* is preferred because is unambiguous */
> > - sprintf(n, "%s/%s/name", sysfs, de->d_name);
> > + snprintf(n, NAME_MAX, "%s/%s/name", sysfs, de->d_name);
>
> OK, now instead of running in a buffer overflow in sprintf you might
> call fopen with a partial (maybe unterminated?) filename. While this is
> definitively better, you should check the return value of snprintf to be
> completely safe here.
To be honest, I never thought the buffer overflows could ever happen,
my motivation to fix them was to allow the code to build in OBS, where
FORTIFY_SOURCE is enabled. So I went for the most simple change that
made gcc happy.
That being said, I have no problem additionally checking the value
returned by snprintf. Something like this?
From: Jean Delvare
Subject: i2cbusses: Check the return value of snprintf
It's very unlikely that these paths will ever be truncated, but
better safe than sorry.
---
tools/i2cbusses.c | 34 ++++++++++++++++++++++++++++------
1 file changed, 28 insertions(+), 6 deletions(-)
--- i2c-tools.orig/tools/i2cbusses.c 2017-11-02 16:17:50.698383029 +0100
+++ i2c-tools/tools/i2cbusses.c 2017-11-08 09:49:40.365339644 +0100
@@ -137,7 +137,7 @@ struct i2c_adap *gather_i2c_busses(void)
FILE *f;
char fstype[NAME_MAX], sysfs[NAME_MAX], n[NAME_MAX];
int foundsysfs = 0;
- int count=0;
+ int len, count = 0;
struct i2c_adap *adapters;
adapters = calloc(BUNCH, sizeof(struct i2c_adap));
@@ -220,18 +220,32 @@ struct i2c_adap *gather_i2c_busses(void)
/* this should work for kernels 2.6.5 or higher and */
/* is preferred because is unambiguous */
- snprintf(n, NAME_MAX, "%s/%s/name", sysfs, de->d_name);
+ len = snprintf(n, NAME_MAX, "%s/%s/name", sysfs, de->d_name);
+ if (len >= NAME_MAX) {
+ fprintf(stderr, "%s: path truncated\n", n);
+ continue;
+ }
f = fopen(n, "r");
/* this seems to work for ISA */
if(f == NULL) {
- snprintf(n, NAME_MAX, "%s/%s/device/name", sysfs, de->d_name);
+ len = snprintf(n, NAME_MAX, "%s/%s/device/name", sysfs,
+ de->d_name);
+ if (len >= NAME_MAX) {
+ fprintf(stderr, "%s: path truncated\n", n);
+ continue;
+ }
f = fopen(n, "r");
}
/* non-ISA is much harder */
/* and this won't find the correct bus name if a driver
has more than one bus */
if(f == NULL) {
- snprintf(n, NAME_MAX, "%s/%s/device", sysfs, de->d_name);
+ len = snprintf(n, NAME_MAX, "%s/%s/device", sysfs,
+ de->d_name);
+ if (len >= NAME_MAX) {
+ fprintf(stderr, "%s: path truncated\n", n);
+ continue;
+ }
if(!(ddir = opendir(n)))
continue;
while ((dde = readdir(ddir)) != NULL) {
@@ -240,8 +254,16 @@ struct i2c_adap *gather_i2c_busses(void)
if (!strcmp(dde->d_name, ".."))
continue;
if ((!strncmp(dde->d_name, "i2c-", 4))) {
- snprintf(n, NAME_MAX, "%s/%s/device/%s/name",
- sysfs, de->d_name, dde->d_name);
+ len = snprintf(n, NAME_MAX,
+ "%s/%s/device/%s/name",
+ sysfs, de->d_name,
+ dde->d_name);
+ if (len >= NAME_MAX) {
+ fprintf(stderr,
+ "%s: path truncated\n",
+ n);
+ continue;
+ }
if((f = fopen(n, "r")))
goto found;
}
--
Jean Delvare
SUSE L3 Support
