swiotlb: fix out-of-bounds TLB allocations with CONFIG_SWIOTLB_DYNAMIC

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 <[email protected]>
Closes: https://lore.kernel.org/linux-iommu/[email protected]/
Fixes: 79636ca ("swiotlb: if swiotlb is full, fall back to a transient memory pool")
Cc: [email protected]
Signed-off-by: Petr Tesarik <[email protected]>
Reviewed-by: Halil Pasic <[email protected]>
Signed-off-by: Christoph Hellwig <[email protected]>

Author: Petr Tesarik

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;
 	}