[PATCH 5.4 110/183] quota: Fix potential NULL pointer dereference

From: Sasha Levin
Date: Mon Mar 25 2024 - 07:57:00 EST

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From: Wang Jianjian <wangjianjian3@xxxxxxxxxx>

[ Upstream commit d0aa72604fbd80c8aabb46eda00535ed35570f1f ]

Below race may cause NULL pointer dereference

P1 P2
dquot_free_inode quota_off
drop_dquot_ref
remove_dquot_ref
dquots = i_dquot(inode)
dquots = i_dquot(inode)
srcu_read_lock
dquots[cnt]) != NULL (1)
dquots[type] = NULL (2)
spin_lock(&dquots[cnt]->dq_dqb_lock) (3)
....

If dquot_free_inode(or other routines) checks inode's quota pointers (1)
before quota_off sets it to NULL(2) and use it (3) after that, NULL pointer
dereference will be triggered.

So let's fix it by using a temporary pointer to avoid this issue.

Signed-off-by: Wang Jianjian <wangjianjian3@xxxxxxxxxx>
Signed-off-by: Jan Kara <jack@xxxxxxx>
Message-Id: <20240202081852.2514092-1-wangjianjian3@xxxxxxxxxx>
Stable-dep-of: 179b8c97ebf6 ("quota: Fix rcu annotations of inode dquot pointers")
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
fs/quota/dquot.c | 98 ++++++++++++++++++++++++++++--------------------
1 file changed, 57 insertions(+), 41 deletions(-)

diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c
index 08ca5b1a5fba5..c4726a1895582 100644
--- a/fs/quota/dquot.c
+++ b/fs/quota/dquot.c
@@ -399,15 +399,17 @@ int dquot_mark_dquot_dirty(struct dquot *dquot)
EXPORT_SYMBOL(dquot_mark_dquot_dirty);

/* Dirtify all the dquots - this can block when journalling */
-static inline int mark_all_dquot_dirty(struct dquot * const *dquot)
+static inline int mark_all_dquot_dirty(struct dquot * const *dquots)
{
int ret, err, cnt;
+ struct dquot *dquot;

ret = err = 0;
for (cnt = 0; cnt < MAXQUOTAS; cnt++) {
- if (dquot[cnt])
+ dquot = srcu_dereference(dquots[cnt], &dquot_srcu);
+ if (dquot)
/* Even in case of error we have to continue */
- ret = mark_dquot_dirty(dquot[cnt]);
+ ret = mark_dquot_dirty(dquot);
if (!err)
err = ret;
}
@@ -1675,6 +1677,7 @@ int __dquot_alloc_space(struct inode *inode, qsize_t number, int flags)
struct dquot_warn warn[MAXQUOTAS];
int reserve = flags & DQUOT_SPACE_RESERVE;
struct dquot **dquots;
+ struct dquot *dquot;

if (!inode_quota_active(inode)) {
if (reserve) {
@@ -1694,27 +1697,26 @@ int __dquot_alloc_space(struct inode *inode, qsize_t number, int flags)
index = srcu_read_lock(&dquot_srcu);
spin_lock(&inode->i_lock);
for (cnt = 0; cnt < MAXQUOTAS; cnt++) {
- if (!dquots[cnt])
+ dquot = srcu_dereference(dquots[cnt], &dquot_srcu);
+ if (!dquot)
continue;
if (reserve) {
- ret = dquot_add_space(dquots[cnt], 0, number, flags,
- &warn[cnt]);
+ ret = dquot_add_space(dquot, 0, number, flags, &warn[cnt]);
} else {
- ret = dquot_add_space(dquots[cnt], number, 0, flags,
- &warn[cnt]);
+ ret = dquot_add_space(dquot, number, 0, flags, &warn[cnt]);
}
if (ret) {
/* Back out changes we already did */
for (cnt--; cnt >= 0; cnt--) {
- if (!dquots[cnt])
+ dquot = srcu_dereference(dquots[cnt], &dquot_srcu);
+ if (!dquot)
continue;
- spin_lock(&dquots[cnt]->dq_dqb_lock);
+ spin_lock(&dquot->dq_dqb_lock);
if (reserve)
- dquot_free_reserved_space(dquots[cnt],
- number);
+ dquot_free_reserved_space(dquot, number);
else
- dquot_decr_space(dquots[cnt], number);
- spin_unlock(&dquots[cnt]->dq_dqb_lock);
+ dquot_decr_space(dquot, number);
+ spin_unlock(&dquot->dq_dqb_lock);
}
spin_unlock(&inode->i_lock);
goto out_flush_warn;
@@ -1745,6 +1747,7 @@ int dquot_alloc_inode(struct inode *inode)
int cnt, ret = 0, index;
struct dquot_warn warn[MAXQUOTAS];
struct dquot * const *dquots;
+ struct dquot *dquot;

if (!inode_quota_active(inode))
return 0;
@@ -1755,17 +1758,19 @@ int dquot_alloc_inode(struct inode *inode)
index = srcu_read_lock(&dquot_srcu);
spin_lock(&inode->i_lock);
for (cnt = 0; cnt < MAXQUOTAS; cnt++) {
- if (!dquots[cnt])
+ dquot = srcu_dereference(dquots[cnt], &dquot_srcu);
+ if (!dquot)
continue;
- ret = dquot_add_inodes(dquots[cnt], 1, &warn[cnt]);
+ ret = dquot_add_inodes(dquot, 1, &warn[cnt]);
if (ret) {
for (cnt--; cnt >= 0; cnt--) {
- if (!dquots[cnt])
+ dquot = srcu_dereference(dquots[cnt], &dquot_srcu);
+ if (!dquot)
continue;
/* Back out changes we already did */
- spin_lock(&dquots[cnt]->dq_dqb_lock);
- dquot_decr_inodes(dquots[cnt], 1);
- spin_unlock(&dquots[cnt]->dq_dqb_lock);
+ spin_lock(&dquot->dq_dqb_lock);
+ dquot_decr_inodes(dquot, 1);
+ spin_unlock(&dquot->dq_dqb_lock);
}
goto warn_put_all;
}
@@ -1787,6 +1792,7 @@ EXPORT_SYMBOL(dquot_alloc_inode);
int dquot_claim_space_nodirty(struct inode *inode, qsize_t number)
{
struct dquot **dquots;
+ struct dquot *dquot;
int cnt, index;

if (!inode_quota_active(inode)) {
@@ -1802,9 +1808,8 @@ int dquot_claim_space_nodirty(struct inode *inode, qsize_t number)
spin_lock(&inode->i_lock);
/* Claim reserved quotas to allocated quotas */
for (cnt = 0; cnt < MAXQUOTAS; cnt++) {
- if (dquots[cnt]) {
- struct dquot *dquot = dquots[cnt];
-
+ dquot = srcu_dereference(dquots[cnt], &dquot_srcu);
+ if (dquot) {
spin_lock(&dquot->dq_dqb_lock);
if (WARN_ON_ONCE(dquot->dq_dqb.dqb_rsvspace < number))
number = dquot->dq_dqb.dqb_rsvspace;
@@ -1829,6 +1834,7 @@ EXPORT_SYMBOL(dquot_claim_space_nodirty);
void dquot_reclaim_space_nodirty(struct inode *inode, qsize_t number)
{
struct dquot **dquots;
+ struct dquot *dquot;
int cnt, index;

if (!inode_quota_active(inode)) {
@@ -1844,9 +1850,8 @@ void dquot_reclaim_space_nodirty(struct inode *inode, qsize_t number)
spin_lock(&inode->i_lock);
/* Claim reserved quotas to allocated quotas */
for (cnt = 0; cnt < MAXQUOTAS; cnt++) {
- if (dquots[cnt]) {
- struct dquot *dquot = dquots[cnt];
-
+ dquot = srcu_dereference(dquots[cnt], &dquot_srcu);
+ if (dquot) {
spin_lock(&dquot->dq_dqb_lock);
if (WARN_ON_ONCE(dquot->dq_dqb.dqb_curspace < number))
number = dquot->dq_dqb.dqb_curspace;
@@ -1873,6 +1878,7 @@ void __dquot_free_space(struct inode *inode, qsize_t number, int flags)
unsigned int cnt;
struct dquot_warn warn[MAXQUOTAS];
struct dquot **dquots;
+ struct dquot *dquot;
int reserve = flags & DQUOT_SPACE_RESERVE, index;

if (!inode_quota_active(inode)) {
@@ -1893,17 +1899,18 @@ void __dquot_free_space(struct inode *inode, qsize_t number, int flags)
int wtype;

warn[cnt].w_type = QUOTA_NL_NOWARN;
- if (!dquots[cnt])
+ dquot = srcu_dereference(dquots[cnt], &dquot_srcu);
+ if (!dquot)
continue;
- spin_lock(&dquots[cnt]->dq_dqb_lock);
- wtype = info_bdq_free(dquots[cnt], number);
+ spin_lock(&dquot->dq_dqb_lock);
+ wtype = info_bdq_free(dquot, number);
if (wtype != QUOTA_NL_NOWARN)
- prepare_warning(&warn[cnt], dquots[cnt], wtype);
+ prepare_warning(&warn[cnt], dquot, wtype);
if (reserve)
- dquot_free_reserved_space(dquots[cnt], number);
+ dquot_free_reserved_space(dquot, number);
else
- dquot_decr_space(dquots[cnt], number);
- spin_unlock(&dquots[cnt]->dq_dqb_lock);
+ dquot_decr_space(dquot, number);
+ spin_unlock(&dquot->dq_dqb_lock);
}
if (reserve)
*inode_reserved_space(inode) -= number;
@@ -1928,6 +1935,7 @@ void dquot_free_inode(struct inode *inode)
unsigned int cnt;
struct dquot_warn warn[MAXQUOTAS];
struct dquot * const *dquots;
+ struct dquot *dquot;
int index;

if (!inode_quota_active(inode))
@@ -1938,16 +1946,16 @@ void dquot_free_inode(struct inode *inode)
spin_lock(&inode->i_lock);
for (cnt = 0; cnt < MAXQUOTAS; cnt++) {
int wtype;
-
warn[cnt].w_type = QUOTA_NL_NOWARN;
- if (!dquots[cnt])
+ dquot = srcu_dereference(dquots[cnt], &dquot_srcu);
+ if (!dquot)
continue;
- spin_lock(&dquots[cnt]->dq_dqb_lock);
- wtype = info_idq_free(dquots[cnt], 1);
+ spin_lock(&dquot->dq_dqb_lock);
+ wtype = info_idq_free(dquot, 1);
if (wtype != QUOTA_NL_NOWARN)
- prepare_warning(&warn[cnt], dquots[cnt], wtype);
- dquot_decr_inodes(dquots[cnt], 1);
- spin_unlock(&dquots[cnt]->dq_dqb_lock);
+ prepare_warning(&warn[cnt], dquot, wtype);
+ dquot_decr_inodes(dquot, 1);
+ spin_unlock(&dquot->dq_dqb_lock);
}
spin_unlock(&inode->i_lock);
mark_all_dquot_dirty(dquots);
@@ -1974,7 +1982,7 @@ int __dquot_transfer(struct inode *inode, struct dquot **transfer_to)
qsize_t rsv_space = 0;
qsize_t inode_usage = 1;
struct dquot *transfer_from[MAXQUOTAS] = {};
- int cnt, ret = 0;
+ int cnt, index, ret = 0;
char is_valid[MAXQUOTAS] = {};
struct dquot_warn warn_to[MAXQUOTAS];
struct dquot_warn warn_from_inodes[MAXQUOTAS];
@@ -2063,8 +2071,16 @@ int __dquot_transfer(struct inode *inode, struct dquot **transfer_to)
spin_unlock(&inode->i_lock);
spin_unlock(&dq_data_lock);

+ /*
+ * These arrays are local and we hold dquot references so we don't need
+ * the srcu protection but still take dquot_srcu to avoid warning in
+ * mark_all_dquot_dirty().
+ */
+ index = srcu_read_lock(&dquot_srcu);
mark_all_dquot_dirty(transfer_from);
mark_all_dquot_dirty(transfer_to);
+ srcu_read_unlock(&dquot_srcu, index);
+
flush_warnings(warn_to);
flush_warnings(warn_from_inodes);
flush_warnings(warn_from_space);
--
2.43.0

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