[PATCH 1/1] swiotlb: fix out-of-bounds TLB allocations with CONFIG_SWIOTLB_DYNAMIC

[Petr Tesarik]

From: Petr Tesarik <petr.tesarik1@xxxxxxxxxxxxxxxxxxx>

Limit the free list length to the size of the IO TLB. Transient pool can be
smaller than IO_TLB_SEGSIZE, but the free list is initialized with the
assumption that the total number of slots is a multiple of IO_TLB_SEGSIZE.
As a result, swiotlb_area_find_slots() may allocate slots past the end of
a transient IO TLB buffer.

Reported-by: Niklas Schnelle <schnelle@xxxxxxxxxxxxx>
Closes: https://lore.kernel.org/linux-iommu/104a8c8fedffd1ff8a2890983e2ec1c26bff6810.camel@xxxxxxxxxxxxx/
Fixes: 79636caad361 ("swiotlb: if swiotlb is full, fall back to a transient memory pool")
Cc: Halil Pasic <pasic@xxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Petr Tesarik <petr.tesarik1@xxxxxxxxxxxxxxxxxxx>
---
 kernel/dma/swiotlb.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index 26202274784f..ec82524ba902 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -283,7 +283,8 @@ static void swiotlb_init_io_tlb_pool(struct io_tlb_pool *mem, phys_addr_t start,
 	}
 
 	for (i = 0; i < mem->nslabs; i++) {
-		mem->slots[i].list = IO_TLB_SEGSIZE - io_tlb_offset(i);
+		mem->slots[i].list = min(IO_TLB_SEGSIZE - io_tlb_offset(i),
+					 mem->nslabs - i);
 		mem->slots[i].orig_addr = INVALID_PHYS_ADDR;
 		mem->slots[i].alloc_size = 0;
 	}
-- 
2.42.1