s390/ism: Zerorize dmb at allocation

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Sashiko reported [1] that 'Missing __GFP_ZERO in folio_alloc() causes
uninitialized kernel memory to be exposed in the receive message buffer'.
An ism dmb is receive-only, so the data is not leaked to a remote peer.
In general the smc kernel module (dibs client) will only push newly
received data to userspace. We still should not have uninitialized data
in a receive buffer.

Since
commit 750afb08ca ("cross-tree: phase out dma_zalloc_coherent()")
dma_alloc_coherent no longer required the __GFP_ZERO flag, but when
commit 83781384a9 ("s390/ism: Properly fix receive message buffer allocation")
switched to folio_alloc(), it should have added back the __GFP_ZERO flag.

Add __GFP_ZERO flag and state in dibs.h that register_dbm() provides
a zerorized buffer (dibs_lo already does).

Link: https://lore.kernel.org/linux-s390/20260903143746.A5CC41F00A3A@smtp.kernel.org/ [1]
Fixes: 83781384a9 ("s390/ism: Properly fix receive message buffer allocation")
Signed-off-by: Alexandra Winter <wintera@linux.ibm.com>
Reviewed-by: Julian Ruess <julianr@linux.ibm.com>
Link: https://patch.msgid.link/20260928151420.383105-1-wintera@linux.ibm.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

...

This commit is contained in:

Alexandra Winter 2026-09-28 17:14:20 +02:00 • committed by Jakub Kicinski

parent 22691f0128

commit a0227fa24e

2 changed files with 5 additions and 4 deletions

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3

drivers/s390/net/ism_drv.c

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6

include/linux/dibs.h

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