5.10-stable review patch. If anyone has any objections, please let me know. ------------------ From: Bryam Vargas commit 6a1f2e5ed9267ca19187038ac635393c165213ac upstream. 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: 5212e11fde4d ("nd_btt: atomic sector updates") Cc: stable@vger.kernel.org Signed-off-by: Bryam Vargas Reviewed-by: Alison Schofield Tested-by: Alison Schofield Link: https://patch.msgid.link/20260620-b4-disp-88b2514b-v1-1-3834e707d232@proton.me Signed-off-by: Alison Schofield Signed-off-by: Greg Kroah-Hartman --- drivers/nvdimm/btt.c | 8 ++++++++ 1 file changed, 8 insertions(+) --- a/drivers/nvdimm/btt.c +++ b/drivers/nvdimm/btt.c @@ -886,6 +886,14 @@ static int discover_arenas(struct btt *b 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),