From 17e83b78bf0f9d9857c6eb100a87143b70d2e12c Mon Sep 17 00:00:00 2001 From: Jakub Kicinski Date: Thu, 10 Jul 2025 17:11:21 -0700 Subject: [PATCH] netlink: make sure we allow at least one dump skb commit a215b5723922f8099078478122f02100e489cb80 upstream. Commit under Fixes tightened up the memory accounting for Netlink sockets. Looks like the accounting is too strict for some existing use cases, Marek reported issues with nl80211 / WiFi iw CLI. To reduce number of iterations Netlink dumps try to allocate messages based on the size of the buffer passed to previous recvmsg() calls. If user space uses a larger buffer in recvmsg() than sk_rcvbuf we will allocate an skb we won't be able to queue. Make sure we always allow at least one skb to be queued. Same workaround is already present in netlink_attachskb(). Alternative would be to cap the allocation size to rcvbuf - rmem_alloc but as I said, the workaround is already present in other places. Reported-by: Marek Szyprowski Link: https://lore.kernel.org/9794af18-4905-46c6-b12c-365ea2f05858@samsung.com Fixes: ae8f160e7eb2 ("netlink: Fix wraparounds of sk->sk_rmem_alloc.") Tested-by: Marek Szyprowski Reviewed-by: Kuniyuki Iwashima Link: https://patch.msgid.link/20250711001121.3649033-1-kuba@kernel.org Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman (cherry picked from commit c31ee1695b6d88042d7bd6b2a77babb70f941451) --- net/netlink/af_netlink.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c index 0b2c7cb1409a..0a412d9a8e5f 100644 --- a/net/netlink/af_netlink.c +++ b/net/netlink/af_netlink.c @@ -2199,11 +2199,11 @@ static int netlink_dump(struct sock *sk, bool lock_taken) struct netlink_ext_ack extack = {}; struct netlink_callback *cb; struct sk_buff *skb = NULL; + unsigned int rmem, rcvbuf; size_t max_recvmsg_len; struct module *module; int err = -ENOBUFS; int alloc_min_size; - unsigned int rmem; int alloc_size; if (!lock_taken) @@ -2235,8 +2235,9 @@ static int netlink_dump(struct sock *sk, bool lock_taken) if (!skb) goto errout_skb; + rcvbuf = READ_ONCE(sk->sk_rcvbuf); rmem = atomic_add_return(skb->truesize, &sk->sk_rmem_alloc); - if (rmem >= READ_ONCE(sk->sk_rcvbuf)) { + if (rmem != skb->truesize && rmem >= rcvbuf) { atomic_sub(skb->truesize, &sk->sk_rmem_alloc); goto errout_skb; }