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ksmbd: fix use-after-free in oplock break notification

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smb2_oplock_break_noti() reads opinfo->conn without any lock and
dereferences it after two allocations which may sleep.  When the
durable handle owning the oplock is disconnected, session_fd_check()
clears opinfo->conn and drops its conn reference under ci->m_lock, and
the last ksmbd_conn_put() frees the connection.  A break triggered by
another connection that races with the teardown can then resurrect the
freed connection: ksmbd_conn_get() is a plain atomic_inc, and the
queued break work later dereferences the stale conn via
ksmbd_conn_write(), a use-after-free reachable by any authenticated
client holding a durable batch oplock.

Thread the caller's inode into the notification path instead of taking
a new reference on it.  Every caller of oplock_break() already holds a
live ksmbd_file (or an explicit ksmbd_inode_lookup_lock() reference,
in the parent lease break paths) on the inode that owns the break
target's oplock list, so ci cannot be freed during the call, and its
lock can be taken without dereferencing opinfo->o_fp, which a
concurrent close may free.  Select and pin the connection under
ci->m_lock, the same lock session_fd_check() and
ksmbd_reopen_durable_fd() use to update opinfo->conn, so a concurrent
detach either loses the race to the clear or keeps the connection
alive until the notification work releases it.  Transfer the reference
to the work item and release it on allocation failures.

Fixes: b003086d76 ("ksmbd: fix NULL-deref of opinfo->conn in oplock/lease break notifiers")
Cc: stable@vger.kernel.org
Signed-off-by: Abdifatah Suruur <suruurism@gmail.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
This commit is contained in:
Abdifatah Suruur 2026-08-29 18:40:22 +03:00 committed by Namjae Jeon
parent 636abbe7a6
commit 0e75389962
1 changed files with 57 additions and 16 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

73
fs/smb/server/oplock.c
View File

@ -924,31 +924,69 @@ static void __smb2_oplock_break_noti(struct work_struct *wk)
ksmbd_conn_put(conn);
}
/*
* Select and pin the connection used for an oplock break before doing any
* allocations which may sleep. The caller of oplock_break() holds a live
* reference on ci (a file being opened, a file being operated on, or an
* explicit ksmbd_inode_lookup_lock() reference in the parent lease break
* paths), so the inode cannot be freed during the call and its lock is
* reachable without dereferencing opinfo->o_fp, which is not pinned by
* the oplock reference and may be freed by a concurrent close.
*
* opinfo->conn is cleared under ci->m_lock by session_fd_check() when the
* durable handle owning the oplock is disconnected, reassigned by
* ksmbd_reopen_durable_fd() under the same lock, and the last
* ksmbd_conn_put() of the old connection frees it. Holding the read lock
* excludes both writers, so the connection cannot be freed while it is
* selected.
*/
static struct ksmbd_conn *smb2_oplock_break_conn_get(struct oplock_info *opinfo,
struct ksmbd_inode *ci)
{
struct ksmbd_conn *conn;
down_read(&ci->m_lock);
conn = READ_ONCE(opinfo->conn);
if (conn && !ksmbd_conn_releasing(conn))
conn = ksmbd_conn_get(conn);
else
conn = NULL;
up_read(&ci->m_lock);
return conn;
}
/**
* smb2_oplock_break_noti() - send smb2 exclusive/batch to level2 oplock
* break command from server to client
* @opinfo: oplock info object
* @ci: inode owning the break target's oplock list, pinned by
* the caller
*
* Return: 0 on success, otherwise error
*/
static int smb2_oplock_break_noti(struct oplock_info *opinfo)
static int smb2_oplock_break_noti(struct oplock_info *opinfo,
struct ksmbd_inode *ci)
{
struct ksmbd_conn *conn;
struct oplock_break_info *br_info;
int ret = 0;
struct ksmbd_work *work;
conn = READ_ONCE(opinfo->conn);
conn = smb2_oplock_break_conn_get(opinfo, ci);
if (!conn)
return ksmbd_invalidate_durable_fd(opinfo->fid);
work = ksmbd_alloc_work_struct();
if (!work)
if (!work) {
ksmbd_conn_put(conn);
return -ENOMEM;
}
br_info = kmalloc_obj(struct oplock_break_info, KSMBD_DEFAULT_GFP);
if (!br_info) {
ksmbd_free_work_struct(work);
ksmbd_conn_put(conn);
return -ENOMEM;
}
@ -957,7 +995,8 @@ static int smb2_oplock_break_noti(struct oplock_info *opinfo)
br_info->open_trunc = opinfo->open_trunc;
work->request_buf = (char *)br_info;
work->conn = ksmbd_conn_get(conn);
/* Transfer the reference acquired by smb2_oplock_break_conn_get(). */
work->conn = conn;
work->sess = opinfo->sess;
ksmbd_conn_r_count_inc(conn);
@ -1154,9 +1193,9 @@ static void wait_lease_breaking(struct oplock_info *opinfo)
}
}
static int oplock_break(struct oplock_info *brk_opinfo, int req_op_level,
struct ksmbd_work *in_work, bool share_break,
bool sync_lease_break)
static int oplock_break(struct oplock_info *brk_opinfo, struct ksmbd_inode *ci,
int req_op_level, struct ksmbd_work *in_work,
bool share_break, bool sync_lease_break)
{
int err = 0;
bool sent_interim = false;
@ -1298,7 +1337,7 @@ static int oplock_break(struct oplock_info *brk_opinfo, int req_op_level,
}
}
err = smb2_oplock_break_noti(brk_opinfo);
err = smb2_oplock_break_noti(brk_opinfo, ci);
ksmbd_debug(OPLOCK, "oplock granted = %d\n", brk_opinfo->level);
if (brk_opinfo->op_state == OPLOCK_CLOSING)
@ -1326,13 +1365,14 @@ static int oplock_break_add(struct list_head *head, struct oplock_info *opinfo)
return 0;
}
static void oplock_break_drain_none(struct list_head *head)
static void oplock_break_drain_none(struct list_head *head,
struct ksmbd_inode *ci)
{
struct oplock_break_entry *ent, *tmp;
list_for_each_entry_safe(ent, tmp, head, list) {
oplock_break(ent->opinfo, SMB2_OPLOCK_LEVEL_NONE, NULL, false,
false);
oplock_break(ent->opinfo, ci, SMB2_OPLOCK_LEVEL_NONE, NULL,
false, false);
list_del(&ent->list);
opinfo_put(ent->opinfo);
kfree(ent);
@ -1481,7 +1521,7 @@ void smb_send_parent_lease_break_noti(struct ksmbd_file *fp,
}
up_read(&p_ci->m_lock);
oplock_break_drain_none(&brk_list);
oplock_break_drain_none(&brk_list, p_ci);
ksmbd_inode_put(p_ci);
}
@ -1525,7 +1565,7 @@ void smb_lazy_parent_lease_break_close(struct ksmbd_file *fp)
}
up_read(&p_ci->m_lock);
oplock_break_drain_none(&brk_list);
oplock_break_drain_none(&brk_list, p_ci);
ksmbd_inode_put(p_ci);
}
@ -1665,7 +1705,7 @@ int smb_grant_oplock(struct ksmbd_work *work, int req_op_level, u64 pid,
prev_durable_detached = prev_op_snapshot.durable_detached;
prev_fid = prev_op_snapshot.fid;
err = oplock_break(prev_opinfo, break_level, work,
err = oplock_break(prev_opinfo, ci, break_level, work,
share_ret < 0 && prev_opinfo->is_lease, false);
if (prev_durable_detached || (prev_durable_open && err == -ENOENT))
ksmbd_invalidate_durable_fd(prev_fid);
@ -1771,7 +1811,8 @@ static bool smb_break_all_write_oplock(struct ksmbd_work *work,
}
brk_opinfo->open_trunc = is_trunc;
oplock_break(brk_opinfo, SMB2_OPLOCK_LEVEL_II, work, false, false);
oplock_break(brk_opinfo, fp->f_ci, SMB2_OPLOCK_LEVEL_II, work, false,
false);
sent_break = true;
opinfo_put(brk_opinfo);
@ -1863,7 +1904,7 @@ static void __smb_break_all_levII_oplock(struct ksmbd_work *work,
brk_op->op_state = OPLOCK_STATE_NONE;
spin_unlock(&brk_op->state_lock);
} else {
oplock_break(brk_op,
oplock_break(brk_op, ci,
brk_op->is_lease && !is_trunc ?
SMB2_OPLOCK_LEVEL_II : SMB2_OPLOCK_LEVEL_NONE,
send_interim && !sent_interim ? work : NULL,