On Thu, Sep 17, 2020 at 07:38:57PM +0800, Xiongfeng Wang wrote:
> I am not sure if snprintf will return a value larger than its second input
> paramter 'size'.
The comment over snprintf() says
* The return value is the number of characters which would be
* generated for the given input, excluding the trailing null,
* as per ISO C99. If the return is greater than or equal to
* @size, the resulting string is truncated.
And let's try it, see diff at the end. Now look what that produces:
[ 2.594796] kernel_init: len: 16, str: [A lo]
it returns 16 for len even though the buffer is 5 chars long. So in our
patch, we'd increment by 16 which would be wrong.
Now let's use scnprintf():
[ 2.700142] kernel_init: len: 4, str: [A lo]
Much better. Lemme do that.
> Not sure whether we need to check 'len' equals to 0.
> if (len <= 0) ?
Yeah, lemme fix that too, so we have now incrementally ontop:
---
diff --git a/drivers/edac/edac_mc_sysfs.c b/drivers/edac/edac_mc_sysfs.c
index fa0551c81e63..c56e0004b39e 100644
--- a/drivers/edac/edac_mc_sysfs.c
+++ b/drivers/edac/edac_mc_sysfs.c
@@ -822,18 +822,17 @@ static ssize_t mci_max_location_show(struct device *dev,
int i, n;
for (i = 0; i < mci->n_layers; i++) {
- n = snprintf(p, len, "%s %d ",
- edac_layer_name[mci->layers[i].type],
- mci->layers[i].size - 1);
-
+ n = scnprintf(p, len, "%s %d ",
+ edac_layer_name[mci->layers[i].type],
+ mci->layers[i].size - 1);
len -= n;
- if (len < 0)
+ if (len <= 0)
goto out;
p += n;
}
- p += snprintf(p, len, "\n");
+ p += scnprintf(p, len, "\n");
out:
return p - data;
}
---
Test diff:
---
diff --git a/init/main.c b/init/main.c
index ae78fb68d231..e2d6110d3a3d 100644
--- a/init/main.c
+++ b/init/main.c
@@ -1397,7 +1397,8 @@ void __weak free_initmem(void)
static int __ref kernel_init(void *unused)
{
- int ret;
+ char str[5];
+ int ret, len;
kernel_init_freeable();
/* need to finish all async __init code before freeing the memory */
@@ -1419,6 +1420,11 @@ static int __ref kernel_init(void *unused)
do_sysctl_args();
+ len = snprintf(str, 5, "A longer string\n");
+
+ pr_info("%s: len: %d, str: [%s]\n",
+ __func__, len, str);
+
if (ramdisk_execute_command) {
ret = run_init_process(ramdisk_execute_command);
if (!ret)
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
