| Message ID | 20210413070848.7261-1-jonathon.reinhart@gmail.com (mailing list archive) |
|---|---|
| State | Superseded |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | net: Make tcp_allowed_congestion_control readonly in non-init netns | expand |
| Context | Check | Description |
|---|---|---|
| netdev/cover_letter | success | Link |
| netdev/fixes_present | success | Link |
| netdev/patch_count | success | Link |
| netdev/tree_selection | success | Guessed tree name to be net-next |
| netdev/subject_prefix | warning | Target tree name not specified in the subject |
| netdev/cc_maintainers | success | CCed 6 of 6 maintainers |
| netdev/source_inline | success | Was 0 now: 0 |
| netdev/verify_signedoff | success | Link |
| netdev/module_param | success | Was 0 now: 0 |
| netdev/build_32bit | success | Errors and warnings before: 1 this patch: 1 |
| netdev/kdoc | success | Errors and warnings before: 0 this patch: 0 |
| netdev/verify_fixes | fail | Link |
| netdev/checkpatch | warning | WARNING: line length of 81 exceeds 80 columns |
| netdev/build_allmodconfig_warn | success | Errors and warnings before: 1 this patch: 1 |
| netdev/header_inline | success | Link |
On Tue, Apr 13, 2021 at 03:08:48AM -0400, Jonathon Reinhart wrote: > 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@gmail.com> > --- Thanks for catching this. I think this works fine as a fix. What I wonder is whether we have a need to make tcp_allowed_congestion_control per-netns proper. That would be a bit more work of course and we don't need to do it right now. (Fwiw, we should really have a document describing the sysctls which are namespaced and how.) > net/ipv4/sysctl_net_ipv4.c | 16 +++++++++++++--- > 1 file changed, 13 insertions(+), 3 deletions(-) > > diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c > index a09e466ce11d..a62934b9f15a 100644 > --- a/net/ipv4/sysctl_net_ipv4.c > +++ b/net/ipv4/sysctl_net_ipv4.c > @@ -1383,9 +1383,19 @@ static __net_init int ipv4_sysctl_init_net(struct net *net) > 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; > + } > + } Just for future reference if we would need to distinguish between entries that do have data set and such that don't here we could also do the below. This works because the tcp_{available,allowed}_[..] do allocated into a local ctl_table variable anyway. diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c index f55095d3ed16..a1c8f5fe7501 100644 --- a/net/ipv4/sysctl_net_ipv4.c +++ b/net/ipv4/sysctl_net_ipv4.c @@ -877,12 +877,14 @@ static struct ctl_table ipv4_net_table[] = { }, { .procname = "tcp_available_congestion_control", + .data = ERR_PTR(-EINVAL), .maxlen = TCP_CA_BUF_MAX, .mode = 0444, .proc_handler = proc_tcp_available_congestion_control, }, { .procname = "tcp_allowed_congestion_control", + .data = ERR_PTR(-EINVAL), .maxlen = TCP_CA_BUF_MAX, .mode = 0644, .proc_handler = proc_allowed_congestion_control, @@ -1379,8 +1381,18 @@ static __net_init int ipv4_sysctl_init_net(struct net *net) 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 (!IS_ERR(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; + } + } }
On Tue, 13 Apr 2021 03:08:48 -0400 Jonathon Reinhart wrote:
> Fixes: 9cb8e048e5d9: ("net/ipv4/sysctl: show tcp_{allowed, available}_congestion_control in non-initial netns")
nit: no semicolon after the hash
On Tue, Apr 13, 2021 at 2:23 PM Jakub Kicinski <kuba@kernel.org> wrote: > > On Tue, 13 Apr 2021 03:08:48 -0400 Jonathon Reinhart wrote: > > Fixes: 9cb8e048e5d9: ("net/ipv4/sysctl: show tcp_{allowed, available}_congestion_control in non-initial netns") > > nit: no semicolon after the hash Oops. scripts/checkpatch.pl didn't catch this, but it looks like patchwork did. You indicated "nit": Shall I resubmit, or can something trivial like this be fixed up when committed? I'm fine either way, I just need to know what's expected. Also, this patch shows up in patchwork as "Not Applicable". I didn't see any notification about that state change, nor do I really know what that means. Was that due to this nit, or something else? Thanks for guiding me through this. Jonathon
On Wed, 14 Apr 2021 17:31:55 -0400 Jonathon Reinhart wrote: > On Tue, Apr 13, 2021 at 2:23 PM Jakub Kicinski <kuba@kernel.org> wrote: > > > > On Tue, 13 Apr 2021 03:08:48 -0400 Jonathon Reinhart wrote: > > > Fixes: 9cb8e048e5d9: ("net/ipv4/sysctl: show tcp_{allowed, available}_congestion_control in non-initial netns") > > > > nit: no semicolon after the hash > > Oops. scripts/checkpatch.pl didn't catch this, but it looks like patchwork did. > > You indicated "nit": Shall I resubmit, or can something trivial like > this be fixed up when committed? I'm fine either way, I just need to > know what's expected. I was just pointing it out, I wasn't 100% sure if it's important enough for DaveM to request a repost. > Also, this patch shows up in patchwork as "Not Applicable". I didn't > see any notification about that state change, nor do I really know > what that means. Was that due to this nit, or something else? > > Thanks for guiding me through this. I think best way forward is to repost with the nit addressed.
diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c index a09e466ce11d..a62934b9f15a 100644 --- a/net/ipv4/sysctl_net_ipv4.c +++ b/net/ipv4/sysctl_net_ipv4.c @@ -1383,9 +1383,19 @@ static __net_init int ipv4_sysctl_init_net(struct net *net) 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);
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@gmail.com> --- net/ipv4/sysctl_net_ipv4.c | 16 +++++++++++++--- 1 file changed, 13 insertions(+), 3 deletions(-)