Linux Kernel DRBD LOGIC BUG in drbd_al_begin_io_nonblock()
CVE-2026-23356 Published on March 25, 2026
drbd: fix "LOGIC BUG" in drbd_al_begin_io_nonblock()
In the Linux kernel, the following vulnerability has been resolved:
drbd: fix "LOGIC BUG" in drbd_al_begin_io_nonblock()
Even though we check that we "should" be able to do lc_get_cumulative()
while holding the device->al_lock spinlock, it may still fail,
if some other code path decided to do lc_try_lock() with bad timing.
If that happened, we logged "LOGIC BUG for enr=...",
but still did not return an error.
The rest of the code now assumed that this request has references
for the relevant activity log extents.
The implcations are that during an active resync, mutual exclusivity of
resync versus application IO is not guaranteed. And a potential crash
at this point may not realizs that these extents could have been target
of in-flight IO and would need to be resynced just in case.
Also, once the request completes, it will give up activity log references it
does not even hold, which will trigger a BUG_ON(refcnt == 0) in lc_put().
Fix:
Do not crash the kernel for a condition that is harmless during normal
operation: also catch "e->refcnt == 0", not only "e == NULL"
when being noisy about "al_complete_io() called on inactive extent %u\n".
And do not try to be smart and "guess" whether something will work, then
be surprised when it does not.
Deal with the fact that it may or may not work. If it does not, remember a
possible "partially in activity log" state (only possible for requests that
cross extent boundaries), and return an error code from
drbd_al_begin_io_nonblock().
A latter call for the same request will then resume from where we left off.
Products Associated with CVE-2026-23356
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Affected Versions
Linux:- Version 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and below 7752569fc78e89794ce28946529850282233f99d is affected.
- Version 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and below e91d8d6565b7819d13dab21d4dbed5b45efba59b is affected.
- Version 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and below eef1390125b660b8b61f9f227a03bb9c5e6d36a5 is affected.
- Version 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and below d1ef3aed4df2ef1fe46befd8f2da9a6ec5445508 is affected.
- Version 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and below f558e5404a72054b525dced1a0c66aa95a144153 is affected.
- Version 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and below ab140365fb62c0bdab22b2f516aff563b2559e3b is affected.
- Version 6.1.167, <= 6.1.* is unaffected.
- Version 6.6.130, <= 6.6.* is unaffected.
- Version 6.12.77, <= 6.12.* is unaffected.
- Version 6.18.17, <= 6.18.* is unaffected.
- Version 6.19.7, <= 6.19.* is unaffected.
- Version 7.0-rc2, <= * is unaffected.