smb: client: delete compound mids on send failure before unlock

Overview

In the Linux kernel, the following vulnerability has been resolved:

smb: client: delete compound mids on send failure before unlock

When sending a compound request fails, smb_send_rqst() kicks off a reconnect. compound_send_recv() still has those mids on pending_mid_q, but it unlocks the server without removing them first.

During reconnect, cifs_abort_connection() walks pending_mid_q and runs each mid callback. With no response yet, those callbacks return credits and drop in_flight. Then compound_send_recv()'s send-error path returns the same credits again. in_flight ends up decremented twice and smb2_add_credits() WARNs.

syzbot hits this during SMB2_negotiate when the socket send fails.

cifs_call_async() already calls delete_mid() before unlock on send failure. Do the same for compound chains and set cancelled_mid[] so the out: path does not delete them again.

Affected

• Linux >= ee258d79159afed52ca9372aeb9c1a51e89b32ee < 70783946f3b5d0c06ec7df0f5e7bec2bfad24efb
• Linux >= ee258d79159afed52ca9372aeb9c1a51e89b32ee < 8f6f8a48399f82f4a83f7b9f25b9707e0062a4f9
• Linux 3c57a0be487088b08d9c88998f911eb4a7ba36e4
• Linux >= 4.20.11 < 4.21
• Linux 5.0

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.