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net: sysctl: allow dump_cpumask to handle higher numbers of CPUs

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This fixes the output of rps_default_mask and flow_limit_cpu_bitmap when
the CPU count is > 448, as it was truncated.

The underlying values are actually stored correctly when writing to
these sysctl but displaying them uses a fixed length temporary buffer in
dump_cpumask. This buffer can be too small if the CPU count is > 448.

Fix this by dynamically allocating the buffer in dump_cpumask, using a
guesstimate of what we need.

Signed-off-by: Antoine Tenart <atenart@kernel.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
This commit is contained in:
Antoine Tenart 2024-10-17 17:24:19 +02:00 committed by Paolo Abeni
parent a8cc8fa145
commit 124afe773b
1 changed files with 23 additions and 9 deletions
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32
net/core/sysctl_net_core.c
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@ -51,22 +51,32 @@ int sysctl_devconf_inherit_init_net __read_mostly;
EXPORT_SYMBOL(sysctl_devconf_inherit_init_net);
#if IS_ENABLED(CONFIG_NET_FLOW_LIMIT) || IS_ENABLED(CONFIG_RPS)
static void dump_cpumask(void *buffer, size_t *lenp, loff_t *ppos,
struct cpumask *mask)
static int dump_cpumask(void *buffer, size_t *lenp, loff_t *ppos,
struct cpumask *mask)
{
char kbuf[128];
char *kbuf;
int len;
if (*ppos || !*lenp) {
*lenp = 0;
return;
return 0;
}
/* CPUs are displayed as a hex bitmap + a comma between each groups of 8
* nibbles (except the last one which has a newline instead).
* Guesstimate the buffer size at the group granularity level.
*/
len = min(DIV_ROUND_UP(nr_cpumask_bits, 32) * (8 + 1), *lenp);
kbuf = kmalloc(len, GFP_KERNEL);
if (!kbuf) {
*lenp = 0;
return -ENOMEM;
}
len = min(sizeof(kbuf), *lenp);
len = scnprintf(kbuf, len, "%*pb", cpumask_pr_args(mask));
if (!len) {
*lenp = 0;
return;
goto free_buf;
}
/* scnprintf writes a trailing null char not counted in the returned
@ -76,6 +86,10 @@ static void dump_cpumask(void *buffer, size_t *lenp, loff_t *ppos,
memcpy(buffer, kbuf, len);
*lenp = len;
*ppos += len;
free_buf:
kfree(kbuf);
return 0;
}
#endif
@ -119,8 +133,8 @@ static int rps_default_mask_sysctl(const struct ctl_table *table, int write,
if (err)
goto done;
} else {
dump_cpumask(buffer, lenp, ppos,
net->core.rps_default_mask ? : cpu_none_mask);
err = dump_cpumask(buffer, lenp, ppos,
net->core.rps_default_mask ? : cpu_none_mask);
}
done:
@ -249,7 +263,7 @@ write_unlock:
}
rcu_read_unlock();
dump_cpumask(buffer, lenp, ppos, mask);
ret = dump_cpumask(buffer, lenp, ppos, mask);
}
done: