[PATCH bpf] xsk: fix broken Tx ring validation

[PATCH bpf] xsk: fix broken Tx ring validation

[Magnus Karlsson]

From: Magnus Karlsson <magnus.karlsson@intel.com>

Fix broken Tx ring validation for AF_XDP. The commit under the Fixes
tag, fixed an off-by-one error in the validation but introduced
another error. Descriptors are now let through even if they straddle a
chunk boundary which they are not allowed to do. Worse is that they
are let through even if they straddle the end of the umem itself,
tricking the kernel to read data outside the allowed umem region which
might or might not be mapped at all.

Fix this by reintroducing the old code, but subtract the length by one
to fix the off-by-one error that the original patch was
addressing. Note that packets of zero length are allowed in the
interface, therefore the test if the length is non-zero.

Fixes: ac31565c2193 ("xsk: Fix for xp_aligned_validate_desc() when len == chunk_size")
Signed-off-by: Magnus Karlsson <magnus.karlsson@intel.com>
---
 net/xdp/xsk_queue.h | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/net/xdp/xsk_queue.h b/net/xdp/xsk_queue.h
index 9d2a89d793c0..9ae13cccfb28 100644
--- a/net/xdp/xsk_queue.h
+++ b/net/xdp/xsk_queue.h
@@ -128,12 +128,15 @@ static inline bool xskq_cons_read_addr_unchecked(struct xsk_queue *q, u64 *addr)
 static inline bool xp_aligned_validate_desc(struct xsk_buff_pool *pool,
 					    struct xdp_desc *desc)
 {
-	u64 chunk;
-
-	if (desc->len > pool->chunk_size)
-		return false;
+	u64 chunk, chunk_end;
 
 	chunk = xp_aligned_extract_addr(pool, desc->addr);
+	if (likely(desc->len)) {
+		chunk_end = xp_aligned_extract_addr(pool, desc->addr + desc->len - 1);
+		if (chunk != chunk_end)
+			return false;
+	}
+
 	if (chunk >= pool->addrs_cnt)
 		return false;
 

base-commit: da5ac772cfe2a03058b0accfac03fad60c46c24d
-- 
2.29.0