[PATCH] smb: client: stop processing a read response after a receive error

[Weiming Shi]

cifs_read_iter_from_socket() may call cifs_reconnect() before returning an
error.  The reconnect path aborts pending mids and invokes their callbacks.
The callback can then release the cifs_io_subrequest containing rdata.

cifs_readv_receive() nevertheless continues after a negative return and may
dereference rdata in cifs_readv_discard().  KASAN reports the resulting
UAF:

  BUG: KASAN: slab-use-after-free in cifs_readv_receive
  Read of size 4 by task cifsd
  cifs_readv_receive (fs/smb/client/transport.c:1284)
  cifs_demultiplex_thread (fs/smb/client/connect.c:1355)
  kthread (kernel/kthread.c:436)
  ret_from_fork (arch/x86/kernel/process.c:158)

  Freed by task 148:
  netfs_put_subrequest (fs/netfs/objects.c:267)
  netfs_read_collection (fs/netfs/read_collect.c:460)
  netfs_wait_for_in_progress (fs/netfs/misc.c:462)

Return the socket error immediately, as this path did before the iterator
conversion.  This also avoids adding a negative length to total_read.

Cc: stable@xxxxxxxxxxxxxxx
Fixes: d08089f649a0 ("cifs: Change the I/O paths to use an iterator rather than a page list")
Reported-by: <co+24c7c12d69e63c6d@xxxxxxx>
Assisted-by: LLM
Signed-off-by: Weiming Shi <bestswngs@xxxxxxxxx>
---
 fs/smb/client/transport.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/smb/client/transport.c b/fs/smb/client/transport.c
index e266859818a441..b7c0ec5d956551 100644
--- a/fs/smb/client/transport.c
+++ b/fs/smb/client/transport.c
@@ -1272,6 +1272,8 @@ cifs_readv_receive(struct TCP_Server_Info *server, struct mid_q_entry *mid)
 #endif
 		length = cifs_read_iter_from_socket(server, &rdata->subreq.io_iter,
 						    data_len);
+	if (length < 0)
+		return length;
 	if (length > 0)
 		rdata->got_bytes += length;
 	server->total_read += length;
-- 
2.56.0