From: Andrew Lukoshko Subject: [PATCH AlmaLinux 10] rxrpc: linearize incoming DATA packet when it has paged frags AlmaLinux-specific backport of the intent of the upstream rxrpc fix posted at https://lore.kernel.org/all/afKV2zGR6rrelPC7@v4bel/ (sibling to upstream commit f4c50a4034e6 in the ESP/xfrm subsystem). The upstream patch can not be cherry-picked against this 6.12 tree: its target lines were introduced by upstream commit d0d5c0cd1e71 ("rxrpc: Use skb_unshare() rather than skb_cow_data()") which is not present here. The age-equivalent code path on AlmaLinux 10 is the centralized skb_unshare() in net/rxrpc/io_thread.c that is run for every DATA packet with a non-zero securityIndex before in-place decryption. skb_unshare() only handles cloned skbs. An skb that is non-cloned but carries paged fragments (skb->data_len != 0) — e.g. pages attached via udp_sendpage() / splice() / MSG_SPLICE_PAGES on a UDP socket carrying rxrpc traffic — slips through and is decrypted in place over data the skb does not own privately. With kernel-modules-partner installed (rxrpc.ko enabled), this is exploitable. Replace the unconditional skb_unshare() with skb_copy() whenever the skb is cloned OR carries paged fragments. skb_copy() always returns a freshly allocated linear skb, so subsequent in-place decryption only touches kernel-owned memory. The original skb is consumed explicitly (skb_unshare did this internally via consume_skb()). Verified to apply with `patch -p1 -F0` (no offset, no fuzz, no rejects) against kernel-6.12.0-124.55.1.el10_1. Fixes: cac2661c53f3 ("rxrpc: Use skb_cow_data() in rxrpc_recvmsg_data()") Signed-off-by: Andrew Lukoshko --- net/rxrpc/io_thread.c | 18 ++++++++++-------- 1 file changed, 10 insertions(+), 8 deletions(-) --- a/net/rxrpc/io_thread.c +++ b/net/rxrpc/io_thread.c @@ -235,16 +235,18 @@ * decryption. */ if (sp->hdr.securityIndex != 0) { - skb = skb_unshare(skb, GFP_ATOMIC); - if (!skb) { - rxrpc_eaten_skb(*_skb, rxrpc_skb_eaten_by_unshare_nomem); - *_skb = NULL; - return just_discard; - } + if (skb_cloned(skb) || skb->data_len) { + struct sk_buff *nskb = skb_copy(skb, GFP_ATOMIC); + + if (!nskb) { + rxrpc_eaten_skb(*_skb, rxrpc_skb_eaten_by_unshare_nomem); + return just_discard; + } - if (skb != *_skb) { rxrpc_eaten_skb(*_skb, rxrpc_skb_eaten_by_unshare); - *_skb = skb; + consume_skb(*_skb); + *_skb = nskb; + skb = nskb; rxrpc_new_skb(skb, rxrpc_skb_new_unshared); sp = rxrpc_skb(skb); } -- 2.43.0