From: Gil Portnoy Date: Thu, 28 May 2026 00:00:00 +0000 (+0000) Subject: ksmbd: fix durable reconnect double-bind race in ksmbd_reopen_durable_fd X-Git-Url: http://git.ipfire.org/gitweb/index.cgi?a=commitdiff_plain;h=7ce4fc40018de07f05f3035241122d992610dbfb;p=thirdparty%2Flinux.git ksmbd: fix durable reconnect double-bind race in ksmbd_reopen_durable_fd Two concurrent same-user DHnC reconnects can both observe fp->conn == NULL before either sets it. ksmbd_reopen_durable_fd() checks fp->conn to guard against a handle already being reconnected, but the check and the binding assignment are not atomic: both threads pass the guard, both call ksmbd_conn_get() on the same fp, and both eventually reach kfree(fp->owner.name) -- a double-free of the owner.name slab object. The double-bound ksmbd_file also causes a write-UAF on the 344-byte ksmbd_file_cache object when a concurrent smb2_close() spins on fp->f_lock after the object has been freed by the losing reconnect path. KASAN on 7.1-rc5 (48-thread concurrent reconnect, 3000 cycles): BUG: KASAN: double-free in ksmbd_reopen_durable_fd+0x268/0x308 BUG: KASAN: slab-use-after-free in _raw_spin_lock+0xac/0x150 Write of size 4 at offset 24 into freed ksmbd_file_cache object Five double-bind windows observed; 63 total KASAN reports triggered. Fix: validate and claim fp->conn under write_lock(&global_ft.lock) so the check-and-claim is atomic. ksmbd_lookup_durable_fd() already treats fp->conn != NULL as "in use" and skips such an fp; setting fp->conn before dropping the lock closes the race. ksmbd_conn_get() is a non-sleeping refcount increment, safe under the rwlock. The rollback path on __open_id() failure also clears fp->conn/tcon under the lock so concurrent readers see a consistent state. Fixes: b1f1e80620de ("ksmbd: centralize ksmbd_conn final release to plug transport leak") Assisted-by: Henry (Claude):claude-opus-4 Signed-off-by: Gil Portnoy Acked-by: Namjae Jeon Signed-off-by: Steve French --- diff --git a/fs/smb/server/vfs_cache.c b/fs/smb/server/vfs_cache.c index 4d2d33df6231..ba3355a6057a 100644 --- a/fs/smb/server/vfs_cache.c +++ b/fs/smb/server/vfs_cache.c @@ -1390,19 +1390,19 @@ int ksmbd_reopen_durable_fd(struct ksmbd_work *work, struct ksmbd_file *fp) struct ksmbd_lock *smb_lock; unsigned int old_f_state; + write_lock(&global_ft.lock); if (!fp->is_durable || fp->conn || fp->tcon) { + write_unlock(&global_ft.lock); pr_err("Invalid durable fd [%p:%p]\n", fp->conn, fp->tcon); return -EBADF; } if (has_file_id(fp->volatile_id)) { + write_unlock(&global_ft.lock); pr_err("Still in use durable fd: %llu\n", fp->volatile_id); return -EBADF; } - old_f_state = fp->f_state; - fp->f_state = FP_NEW; - /* * Initialize fp's connection binding before publishing fp into the * session's file table. If __open_id() is ordered first, a @@ -1413,11 +1413,17 @@ int ksmbd_reopen_durable_fd(struct ksmbd_work *work, struct ksmbd_file *fp) */ fp->conn = ksmbd_conn_get(conn); fp->tcon = work->tcon; + write_unlock(&global_ft.lock); + + old_f_state = fp->f_state; + fp->f_state = FP_NEW; __open_id(&work->sess->file_table, fp, OPEN_ID_TYPE_VOLATILE_ID); if (!has_file_id(fp->volatile_id)) { + write_lock(&global_ft.lock); fp->conn = NULL; fp->tcon = NULL; + write_unlock(&global_ft.lock); ksmbd_conn_put(conn); fp->f_state = old_f_state; return -EBADF;