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cpufreq: stats: Fix buffer overflow detection in trans_stats()

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Commit 3c0897c180 ("cpufreq: Use scnprintf() for avoiding potential
buffer overflow") switched from snprintf to the more secure scnprintf
but never updated the exit condition for PAGE_SIZE.

As the commit say and as scnprintf document, what scnprintf returns what
is actually written not counting the '\0' end char. This results in the
case of len exceeding the size, len set to PAGE_SIZE - 1, as it can be
written at max PAGE_SIZE - 1 (as '\0' is not counted)

Because of len is never set to PAGE_SIZE, the function never break early,
never prints the warning and never return -EFBIG.

Fix this by changing the condition to PAGE_SIZE - 1 to correctly trigger
the error.

Cc: 5.10+ <stable@vger.kernel.org> # 5.10+
Fixes: 3c0897c180 ("cpufreq: Use scnprintf() for avoiding potential buffer overflow")
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
[ rjw: Subject and changelog edits ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
This commit is contained in:
Christian Marangi 2023-10-24 20:30:14 +02:00 committed by Rafael J. Wysocki
parent e7a1b32e43
commit ea167a7fc2
1 changed files with 7 additions and 7 deletions
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14
drivers/cpufreq/cpufreq_stats.c
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@ -131,23 +131,23 @@ static ssize_t show_trans_table(struct cpufreq_policy *policy, char *buf)
len += sysfs_emit_at(buf, len, " From : To\n");
len += sysfs_emit_at(buf, len, " : ");
for (i = 0; i < stats->state_num; i++) {
if (len >= PAGE_SIZE)
if (len >= PAGE_SIZE - 1)
break;
len += sysfs_emit_at(buf, len, "%9u ", stats->freq_table[i]);
}
if (len >= PAGE_SIZE)
return PAGE_SIZE;
if (len >= PAGE_SIZE - 1)
return PAGE_SIZE - 1;
len += sysfs_emit_at(buf, len, "\n");
for (i = 0; i < stats->state_num; i++) {
if (len >= PAGE_SIZE)
if (len >= PAGE_SIZE - 1)
break;
len += sysfs_emit_at(buf, len, "%9u: ", stats->freq_table[i]);
for (j = 0; j < stats->state_num; j++) {
if (len >= PAGE_SIZE)
if (len >= PAGE_SIZE - 1)
break;
if (pending)
@ -157,12 +157,12 @@ static ssize_t show_trans_table(struct cpufreq_policy *policy, char *buf)
len += sysfs_emit_at(buf, len, "%9u ", count);
}
if (len >= PAGE_SIZE)
if (len >= PAGE_SIZE - 1)
break;
len += sysfs_emit_at(buf, len, "\n");
}
if (len >= PAGE_SIZE) {
if (len >= PAGE_SIZE - 1) {
pr_warn_once("cpufreq transition table exceeds PAGE_SIZE. Disabling\n");
return -EFBIG;
}