This is a note to let you know that I've just added the patch titled net: Make tcp_allowed_congestion_control readonly in non-init netns to the 5.11-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: net-make-tcp_allowed_congestion_control-readonly-in-non-init-netns.patch and it can be found in the queue-5.11 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 97684f0970f6e112926de631fdd98d9693c7e5c1 Mon Sep 17 00:00:00 2001 From: Jonathon Reinhart <jonathon.reinhart@xxxxxxxxx> Date: Tue, 13 Apr 2021 03:08:48 -0400 Subject: net: Make tcp_allowed_congestion_control readonly in non-init netns From: Jonathon Reinhart <jonathon.reinhart@xxxxxxxxx> commit 97684f0970f6e112926de631fdd98d9693c7e5c1 upstream. Currently, tcp_allowed_congestion_control is global and writable; writing to it in any net namespace will leak into all other net namespaces. tcp_available_congestion_control and tcp_allowed_congestion_control are the only sysctls in ipv4_net_table (the per-netns sysctl table) with a NULL data pointer; their handlers (proc_tcp_available_congestion_control and proc_allowed_congestion_control) have no other way of referencing a struct net. Thus, they operate globally. Because ipv4_net_table does not use designated initializers, there is no easy way to fix up this one "bad" table entry. However, the data pointer updating logic shouldn't be applied to NULL pointers anyway, so we instead force these entries to be read-only. These sysctls used to exist in ipv4_table (init-net only), but they were moved to the per-net ipv4_net_table, presumably without realizing that tcp_allowed_congestion_control was writable and thus introduced a leak. Because the intent of that commit was only to know (i.e. read) "which congestion algorithms are available or allowed", this read-only solution should be sufficient. The logic added in recent commit 31c4d2f160eb: ("net: Ensure net namespace isolation of sysctls") does not and cannot check for NULL data pointers, because other table entries (e.g. /proc/sys/net/netfilter/nf_log/) have .data=NULL but use other methods (.extra2) to access the struct net. Fixes: 9cb8e048e5d9 ("net/ipv4/sysctl: show tcp_{allowed, available}_congestion_control in non-initial netns") Signed-off-by: Jonathon Reinhart <jonathon.reinhart@xxxxxxxxx> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- net/ipv4/sysctl_net_ipv4.c | 16 +++++++++++++--- 1 file changed, 13 insertions(+), 3 deletions(-) --- a/net/ipv4/sysctl_net_ipv4.c +++ b/net/ipv4/sysctl_net_ipv4.c @@ -1369,9 +1369,19 @@ static __net_init int ipv4_sysctl_init_n if (!table) goto err_alloc; - /* Update the variables to point into the current struct net */ - for (i = 0; i < ARRAY_SIZE(ipv4_net_table) - 1; i++) - table[i].data += (void *)net - (void *)&init_net; + for (i = 0; i < ARRAY_SIZE(ipv4_net_table) - 1; i++) { + if (table[i].data) { + /* Update the variables to point into + * the current struct net + */ + table[i].data += (void *)net - (void *)&init_net; + } else { + /* Entries without data pointer are global; + * Make them read-only in non-init_net ns + */ + table[i].mode &= ~0222; + } + } } net->ipv4.ipv4_hdr = register_net_sysctl(net, "net/ipv4", table); Patches currently in stable-queue which might be from jonathon.reinhart@xxxxxxxxx are queue-5.11/net-make-tcp_allowed_congestion_control-readonly-in-non-init-netns.patch