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mirror_zfs/module/zfs/dataset_kstats.c
Richard Yao 97143b9d31 Introduce kmem_scnprintf() 
`snprintf()` is meant to protect against buffer overflows, but operating
on the buffer using its return value, possibly by calling it again, can
cause a buffer overflow, because it will return how many characters it
would have written if it had enough space even when it did not. In a
number of places, we repeatedly call snprintf() by successively
incrementing a buffer offset and decrementing a buffer length, by its
return value. This is a potentially unsafe usage of `snprintf()`
whenever the buffer length is reached. CodeQL complained about this.

To fix this, we introduce `kmem_scnprintf()`, which will return 0 when
the buffer is zero or the number of written characters, minus 1 to
exclude the NULL character, when the buffer was too small. In all other
cases, it behaves like snprintf(). The name is inspired by the Linux and
XNU kernels' `scnprintf()`. The implementation was written before I
thought to look at `scnprintf()` and had a good name for it, but it
turned out to have identical semantics to the Linux kernel version.
That lead to the name, `kmem_scnprintf()`.

CodeQL only catches this issue in loops, so repeated use of snprintf()
outside of a loop was not caught. As a result, a thorough audit of the
codebase was done to examine all instances of `snprintf()` usage for
potential problems and a few were caught. Fixes for them are included in
this patch.

Unfortunately, ZED is one of the places where `snprintf()` is
potentially used incorrectly. Since using `kmem_scnprintf()` in it would
require changing how it is linked, we modify its usage to make it safe,
no matter what buffer length is used. In addition, there was a bug in
the use of the return value where the NULL format character was not
being written by pwrite(). That has been fixed.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Richard Yao <richard.yao@alumni.stonybrook.edu>
Closes #14098
2022-10-29 13:05:11 -07:00

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/*
* CDDL HEADER START
*
* The contents of this file are subject to the terms of the
* Common Development and Distribution License (the "License").
* You may not use this file except in compliance with the License.
*
* You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
* or https://opensource.org/licenses/CDDL-1.0.
* See the License for the specific language governing permissions
* and limitations under the License.
*
* When distributing Covered Code, include this CDDL HEADER in each
* file and include the License file at usr/src/OPENSOLARIS.LICENSE.
* If applicable, add the following below this CDDL HEADER, with the
* fields enclosed by brackets "[]" replaced with your own identifying
* information: Portions Copyright [yyyy] [name of copyright owner]
*
* CDDL HEADER END
*/
/*
* Copyright (c) 2018 by Delphix. All rights reserved.
* Copyright (c) 2018 Datto Inc.
*/
#include <sys/dataset_kstats.h>
#include <sys/dmu_objset.h>
#include <sys/dsl_dataset.h>
#include <sys/spa.h>
static dataset_kstat_values_t empty_dataset_kstats = {
{ "dataset_name", KSTAT_DATA_STRING },
{ "writes", KSTAT_DATA_UINT64 },
{ "nwritten", KSTAT_DATA_UINT64 },
{ "reads", KSTAT_DATA_UINT64 },
{ "nread", KSTAT_DATA_UINT64 },
{ "nunlinks", KSTAT_DATA_UINT64 },
{ "nunlinked", KSTAT_DATA_UINT64 },
{
{ "zil_commit_count", KSTAT_DATA_UINT64 },
{ "zil_commit_writer_count", KSTAT_DATA_UINT64 },
{ "zil_itx_count", KSTAT_DATA_UINT64 },
{ "zil_itx_indirect_count", KSTAT_DATA_UINT64 },
{ "zil_itx_indirect_bytes", KSTAT_DATA_UINT64 },
{ "zil_itx_copied_count", KSTAT_DATA_UINT64 },
{ "zil_itx_copied_bytes", KSTAT_DATA_UINT64 },
{ "zil_itx_needcopy_count", KSTAT_DATA_UINT64 },
{ "zil_itx_needcopy_bytes", KSTAT_DATA_UINT64 },
{ "zil_itx_metaslab_normal_count", KSTAT_DATA_UINT64 },
{ "zil_itx_metaslab_normal_bytes", KSTAT_DATA_UINT64 },
{ "zil_itx_metaslab_slog_count", KSTAT_DATA_UINT64 },
{ "zil_itx_metaslab_slog_bytes", KSTAT_DATA_UINT64 }
}
};
static int
dataset_kstats_update(kstat_t *ksp, int rw)
{
dataset_kstats_t *dk = ksp->ks_private;
dataset_kstat_values_t *dkv = ksp->ks_data;
ASSERT3P(dk->dk_kstats->ks_data, ==, dkv);
if (rw == KSTAT_WRITE)
return (EACCES);
dkv->dkv_writes.value.ui64 =
wmsum_value(&dk->dk_sums.dss_writes);
dkv->dkv_nwritten.value.ui64 =
wmsum_value(&dk->dk_sums.dss_nwritten);
dkv->dkv_reads.value.ui64 =
wmsum_value(&dk->dk_sums.dss_reads);
dkv->dkv_nread.value.ui64 =
wmsum_value(&dk->dk_sums.dss_nread);
dkv->dkv_nunlinks.value.ui64 =
wmsum_value(&dk->dk_sums.dss_nunlinks);
dkv->dkv_nunlinked.value.ui64 =
wmsum_value(&dk->dk_sums.dss_nunlinked);
zil_kstat_values_update(&dkv->dkv_zil_stats, &dk->dk_zil_sums);
return (0);
}
int
dataset_kstats_create(dataset_kstats_t *dk, objset_t *objset)
{
/*
* There should not be anything wrong with having kstats for
* snapshots. Since we are not sure how useful they would be
* though nor how much their memory overhead would matter in
* a filesystem with many snapshots, we skip them for now.
*/
if (dmu_objset_is_snapshot(objset))
return (0);
/*
* At the time of this writing, KSTAT_STRLEN is 255 in Linux,
* and the spa_name can theoretically be up to 256 characters.
* In reality though the spa_name can be 240 characters max
* [see origin directory name check in pool_namecheck()]. Thus,
* the naming scheme for the module name below should not cause
* any truncations. In the event that a truncation does happen
* though, due to some future change, we silently skip creating
* the kstat and log the event.
*/
char kstat_module_name[KSTAT_STRLEN];
int n = snprintf(kstat_module_name, sizeof (kstat_module_name),
"zfs/%s", spa_name(dmu_objset_spa(objset)));
if (n < 0) {
zfs_dbgmsg("failed to create dataset kstat for objset %lld: "
" snprintf() for kstat module name returned %d",
(unsigned long long)dmu_objset_id(objset), n);
return (SET_ERROR(EINVAL));
} else if (n >= KSTAT_STRLEN) {
zfs_dbgmsg("failed to create dataset kstat for objset %lld: "
"kstat module name length (%d) exceeds limit (%d)",
(unsigned long long)dmu_objset_id(objset),
n, KSTAT_STRLEN);
return (SET_ERROR(ENAMETOOLONG));
}
char kstat_name[KSTAT_STRLEN];
n = snprintf(kstat_name, sizeof (kstat_name), "objset-0x%llx",
(unsigned long long)dmu_objset_id(objset));
if (n < 0) {
zfs_dbgmsg("failed to create dataset kstat for objset %lld: "
" snprintf() for kstat name returned %d",
(unsigned long long)dmu_objset_id(objset), n);
return (SET_ERROR(EINVAL));
} else if (n >= KSTAT_STRLEN) {
zfs_dbgmsg("failed to create dataset kstat for objset %lld: "
"kstat name length (%d) exceeds limit (%d)",
(unsigned long long)dmu_objset_id(objset),
n, KSTAT_STRLEN);
return (SET_ERROR(ENAMETOOLONG));
}
kstat_t *kstat = kstat_create(kstat_module_name, 0, kstat_name,
"dataset", KSTAT_TYPE_NAMED,
sizeof (empty_dataset_kstats) / sizeof (kstat_named_t),
KSTAT_FLAG_VIRTUAL);
if (kstat == NULL)
return (SET_ERROR(ENOMEM));
dataset_kstat_values_t *dk_kstats =
kmem_alloc(sizeof (empty_dataset_kstats), KM_SLEEP);
memcpy(dk_kstats, &empty_dataset_kstats,
sizeof (empty_dataset_kstats));
char *ds_name = kmem_zalloc(ZFS_MAX_DATASET_NAME_LEN, KM_SLEEP);
dsl_dataset_name(objset->os_dsl_dataset, ds_name);
KSTAT_NAMED_STR_PTR(&dk_kstats->dkv_ds_name) = ds_name;
KSTAT_NAMED_STR_BUFLEN(&dk_kstats->dkv_ds_name) =
ZFS_MAX_DATASET_NAME_LEN;
kstat->ks_data = dk_kstats;
kstat->ks_update = dataset_kstats_update;
kstat->ks_private = dk;
kstat->ks_data_size += ZFS_MAX_DATASET_NAME_LEN;
wmsum_init(&dk->dk_sums.dss_writes, 0);
wmsum_init(&dk->dk_sums.dss_nwritten, 0);
wmsum_init(&dk->dk_sums.dss_reads, 0);
wmsum_init(&dk->dk_sums.dss_nread, 0);
wmsum_init(&dk->dk_sums.dss_nunlinks, 0);
wmsum_init(&dk->dk_sums.dss_nunlinked, 0);
zil_sums_init(&dk->dk_zil_sums);
dk->dk_kstats = kstat;
kstat_install(kstat);
return (0);
}
void
dataset_kstats_destroy(dataset_kstats_t *dk)
{
if (dk->dk_kstats == NULL)
return;
dataset_kstat_values_t *dkv = dk->dk_kstats->ks_data;
kstat_delete(dk->dk_kstats);
dk->dk_kstats = NULL;
kmem_free(KSTAT_NAMED_STR_PTR(&dkv->dkv_ds_name),
KSTAT_NAMED_STR_BUFLEN(&dkv->dkv_ds_name));
kmem_free(dkv, sizeof (empty_dataset_kstats));
wmsum_fini(&dk->dk_sums.dss_writes);
wmsum_fini(&dk->dk_sums.dss_nwritten);
wmsum_fini(&dk->dk_sums.dss_reads);
wmsum_fini(&dk->dk_sums.dss_nread);
wmsum_fini(&dk->dk_sums.dss_nunlinks);
wmsum_fini(&dk->dk_sums.dss_nunlinked);
zil_sums_fini(&dk->dk_zil_sums);
}
void
dataset_kstats_update_write_kstats(dataset_kstats_t *dk,
int64_t nwritten)
{
ASSERT3S(nwritten, >=, 0);
if (dk->dk_kstats == NULL)
return;
wmsum_add(&dk->dk_sums.dss_writes, 1);
wmsum_add(&dk->dk_sums.dss_nwritten, nwritten);
}
void
dataset_kstats_update_read_kstats(dataset_kstats_t *dk,
int64_t nread)
{
ASSERT3S(nread, >=, 0);
if (dk->dk_kstats == NULL)
return;
wmsum_add(&dk->dk_sums.dss_reads, 1);
wmsum_add(&dk->dk_sums.dss_nread, nread);
}
void
dataset_kstats_update_nunlinks_kstat(dataset_kstats_t *dk, int64_t delta)
{
if (dk->dk_kstats == NULL)
return;
wmsum_add(&dk->dk_sums.dss_nunlinks, delta);
}
void
dataset_kstats_update_nunlinked_kstat(dataset_kstats_t *dk, int64_t delta)
{
if (dk->dk_kstats == NULL)
return;
wmsum_add(&dk->dk_sums.dss_nunlinked, delta);
}
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