Subj : src/sbbs3/netmail.cpp
To   : Git commit to main/sbbs/master
From : Rob Swindell (on Debian Linux)
Date : Tue Sep 15 2026 20:47:46

https://gitlab.synchro.net/main/sbbs/-/commit/93e3598ffb0d8f368643561a
Modified Files:
	src/sbbs3/netmail.cpp
Log Message:
Hold the SMB header lock across the QWK netmail data allocation

sbbs_t::qwktonetmail() allocated message data storage without holding
smb_locksmbhdr(). Every other allocation site takes it across the
allocation; this one acquired it only indirectly, when smb_addmsghdr()
locks internally some fifty lines later, by which point the data blocks
had already been chosen and written.

smb_allocdat() scans the .sda for a run of free blocks and only then
writes their reference counts, so the window between choosing a run and
claiming it spans the rest of the scan. Two writers allocating
concurrently, one of them on this path, can settle on the same run and
produce two messages whose data storage overlaps, which chksmb reports
as duplicated or corrupt data records. Header allocation is unaffected,
being done inside smb_addmsghdr() under the lock it takes itself.

The window is far narrower under fast allocation, which seeks to EOF and
claims the blocks immediately, so switching a mail base to that storage
mode makes this class of error appear to stop without fixing it.

issue #1241

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
--- SBBSecho 3.37-Linux
 * Origin: Vertrauen - [vert/cvs/bbs].synchro.net (1:103/705)

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