CVE-2024-42256

What it actually does

Incorrect server repick during CIFS subrequest retry causes in_flight counter increment and decrement to occur on different server records, resulting in misaccounting and a warning in smb2_add_credits.

Why it matters to the business

Kernel warnings and potential instability during SMB/CIFS writes, especially in multichannel mode against Azure servers, affecting file serving and storage reliability on Linux systems.

How an attack unfolds

No attacker exploitation path exists; the flaw is a logic error triggered by netfs retry handling in cifs_prepare_write followed by smb2_async_writev, manifesting under test workloads such as generic/249.

How to fix it

Upgrade the Linux kernel to version 6.10.1 or apply commit b1d0a566769b6fb3795b5289fc1daf9e0638d97a; remove the server repick logic from smb2_async_writev.

How to confirm the fix worked

Confirm kernel version is at or above 6.10.1 and verify absence of the smb2_add_credits warning during CIFS multichannel write operations and xfstests.

How to detect it

Search kernel logs for the exact warning string from smb2_add_credits and stack traces involving smb2_writev_callback or cifs_demultiplex_thread during CIFS activity.

• WARNING: CPU: .* PID: .* at fs/smb/client/smb2ops.c:97 smb2_add_credits
• smb2_writev_callback+0x334/0x560 [cifs]

What your security team should do

• Upgrade to fixed kernel version 6.10.1 immediately on all systems using CIFS
• Monitor kernel logs for smb2_add_credits warnings
• Test CIFS multichannel configurations after patching