FAILED: patch "[PATCH] xsk: Add missing check on user supplied headroom size" failed to apply to 4.19-stable tree

The patch below does not apply to the 4.19-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 99e3a236dd43d06c65af0a2ef9cb44306aef6e02 Mon Sep 17 00:00:00 2001
From: Magnus Karlsson <[email protected]>
Date: Tue, 14 Apr 2020 09:35:15 +0200
Subject: [PATCH] xsk: Add missing check on user supplied headroom size

Add a check that the headroom cannot be larger than the available space in the chunk. In the current code, a malicious user can set the headroom to a value larger than the chunk size minus the fixed XDP headroom. That way packets with a length larger than the supported size in the umem could get accepted and result in an out-of-bounds write.

index fa7bb5e060d0..ed7a6060f73c 100644
@@ -343,7 +343,7 @@ static int xdp_umem_reg(struct xdp_umem *umem, struct xdp_umem_reg *mr)
 	u32 chunk_size = mr->chunk_size, headroom = mr->headroom;
 	unsigned int chunks, chunks_per_page;
 	u64 addr = mr->addr, size = mr->len;
-	int size_chk, err;
+	int err;
 
 	if (chunk_size < XDP_UMEM_MIN_CHUNK_SIZE || chunk_size > PAGE_SIZE) {
 		/* Strictly speaking we could support this, if:

@@ -382,8 +382,7 @@ static int xdp_umem_reg(struct xdp_umem *umem, struct xdp_umem_reg *mr)
 			return -EINVAL;
 	}
 
-	size_chk = chunk_size - headroom - XDP_PACKET_HEADROOM;
-	if (size_chk < 0)
+	if (headroom >= chunk_size - XDP_PACKET_HEADROOM)
 		return -EINVAL;
 
 	umem->address = (unsigned long)addr;

Conflict with 624676e78899 ("xdp: xdp_umem: replace kmap on vmap for umem map") around 'i' going away. Fixed and queued for 4.19.

Thanks,
Sasha