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nvdimm/btt: reject an arena whose nfree is below the lane count

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The BTT info block's nfree field, the number of reserve free blocks, is
read from the medium without validation.  btt_freelist_init() and
btt_rtt_init() size the per-lane freelist[] and rtt[] arrays by nfree,
but the I/O path indexes them by the lane from nd_region_acquire_lane(),
which is bounded by nd_region->num_lanes (ND_MAX_LANES), not by nfree.
A crafted or foreign arena whose nfree is below the lane count makes
freelist[lane]/rtt[lane] run past the allocation: an out-of-bounds write.

btt.rst documents the nlanes = min(nfree, num_cpus) invariant, which the
code does not currently honor: num_lanes is ND_MAX_LANES regardless of
nfree.  Reject an arena whose nfree is below num_lanes at discovery,
before the per-lane arrays are allocated, enforcing that invariant.

Fixes: 5212e11fde ("nd_btt: atomic sector updates")
Cc: stable@vger.kernel.org
Signed-off-by: Bryam Vargas <hexlabsecurity@proton.me>
Reviewed-by: Alison Schofield <alison.schofield@intel.com>
Tested-by: Alison Schofield <alison.schofield@intel.com>
Link: https://patch.msgid.link/20260620-b4-disp-88b2514b-v1-1-3834e707d232@proton.me
Signed-off-by: Alison Schofield <alison.schofield@intel.com>
This commit is contained in:
Bryam Vargas 2026-06-20 16:41:31 -05:00 committed by Alison Schofield
parent 18f9124248
commit 6a1f2e5ed9
1 changed files with 8 additions and 0 deletions
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8
drivers/nvdimm/btt.c
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@ -883,6 +883,14 @@ static int discover_arenas(struct btt *btt)
arena->external_lba_start = cur_nlba;
parse_arena_meta(arena, super, cur_off);
if (arena->nfree < btt->nd_region->num_lanes) {
dev_err(to_dev(arena),
"nfree %u smaller than lane count %d\n",
arena->nfree, btt->nd_region->num_lanes);
ret = -ENODEV;
goto out;
}
ret = log_set_indices(arena);
if (ret) {
dev_err(to_dev(arena),