[PATCH AUTOSEL 4.19 34/79] fs/quota: handle overflows of sysctl fs.quota.* and report as unsigned long

Sasha Levin
2019-12-11T15:44:52Z

From: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>

[ Upstream commit 6fcbcec9cfc7b3c6a2c1f1a23ebacedff7073e0a ]

Quota statistics counted as 64-bit per-cpu counter. Reading sums per-cpu
fractions as signed 64-bit int, filters negative values and then reports
lower half as signed 32-bit int.

Result may looks like:

fs.quota.allocated_dquots = 22327
fs.quota.cache_hits = -489852115
fs.quota.drops = -487288718
fs.quota.free_dquots = 22083
fs.quota.lookups = -486883485
fs.quota.reads = 22327
fs.quota.syncs = 335064
fs.quota.writes = 3088689

Values bigger than 2^31-1 reported as negative.

All counters except "allocated_dquots" and "free_dquots" are monotonic,
thus they should be reported as is without filtering negative values.

Kernel doesn't have generic helper for 64-bit sysctl yet,
let's use at least unsigned long.

Link: https://lore.kernel.org/r/157337934693.2078.9842146413181153727.stgit@buzz
Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/quota/dquot.c | 29 +++++++++++++++++------------
include/linux/quota.h | 2 +-
2 files changed, 18 insertions(+), 13 deletions(-)

diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c
index dd1783ea7003c..e1e35bc9e497e 100644
--- a/fs/quota/dquot.c
+++ b/fs/quota/dquot.c
@@ -2852,68 +2852,73 @@ EXPORT_SYMBOL(dquot_quotactl_sysfile_ops);
static int do_proc_dqstats(struct ctl_table *table, int write,
void __user *buffer, size_t *lenp, loff_t *ppos)
{
- unsigned int type = (int *)table->data - dqstats.stat;
+ unsigned int type = (unsigned long *)table->data - dqstats.stat;
+ s64 value = percpu_counter_sum(&dqstats.counter[type]);
+
+ /* Filter negative values for non-monotonic counters */
+ if (value < 0 && (type == DQST_ALLOC_DQUOTS ||
+ type == DQST_FREE_DQUOTS))
+ value = 0;

/* Update global table */
- dqstats.stat[type] =
- percpu_counter_sum_positive(&dqstats.counter[type]);
- return proc_dointvec(table, write, buffer, lenp, ppos);
+ dqstats.stat[type] = value;
+ return proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
}

static struct ctl_table fs_dqstats_table[] = {
{
.procname = "lookups",
.data = &dqstats.stat[DQST_LOOKUPS],
- .maxlen = sizeof(int),
+ .maxlen = sizeof(unsigned long),
.mode = 0444,
.proc_handler = do_proc_dqstats,
},
{
.procname = "drops",
.data = &dqstats.stat[DQST_DROPS],
- .maxlen = sizeof(int),
+ .maxlen = sizeof(unsigned long),
.mode = 0444,
.proc_handler = do_proc_dqstats,
},
{
.procname = "reads",
.data = &dqstats.stat[DQST_READS],
- .maxlen = sizeof(int),
+ .maxlen = sizeof(unsigned long),
.mode = 0444,
.proc_handler = do_proc_dqstats,
},
{
.procname = "writes",
.data = &dqstats.stat[DQST_WRITES],
- .maxlen = sizeof(int),
+ .maxlen = sizeof(unsigned long),
.mode = 0444,
.proc_handler = do_proc_dqstats,
},
{
.procname = "cache_hits",
.data = &dqstats.stat[DQST_CACHE_HITS],
- .maxlen = sizeof(int),
+ .maxlen = sizeof(unsigned long),
.mode = 0444,
.proc_handler = do_proc_dqstats,
},
{
.procname = "allocated_dquots",
.data = &dqstats.stat[DQST_ALLOC_DQUOTS],
- .maxlen = sizeof(int),
+ .maxlen = sizeof(unsigned long),
.mode = 0444,
.proc_handler = do_proc_dqstats,
},
{
.procname = "free_dquots",
.data = &dqstats.stat[DQST_FREE_DQUOTS],
- .maxlen = sizeof(int),
+ .maxlen = sizeof(unsigned long),
.mode = 0444,
.proc_handler = do_proc_dqstats,
},
{
.procname = "syncs",
.data = &dqstats.stat[DQST_SYNCS],
- .maxlen = sizeof(int),
+ .maxlen = sizeof(unsigned long),
.mode = 0444,
.proc_handler = do_proc_dqstats,
},
diff --git a/include/linux/quota.h b/include/linux/quota.h
index f32dd270b8e3f..27aab84fcbaac 100644
--- a/include/linux/quota.h
+++ b/include/linux/quota.h
@@ -263,7 +263,7 @@ enum {
};

struct dqstats {
- int stat[_DQST_DQSTAT_LAST];
+ unsigned long stat[_DQST_DQSTAT_LAST];
struct percpu_counter counter[_DQST_DQSTAT_LAST];
};

--
2.20.1