Re: [net RFC v1 1/1] page_pool: fix NULL dereference crash

Toke Høiland-Jørgensen
2022-01-24T12:13:02Z

Alexei Starovoitov <alexei.starovoitov@gmail.com> writes:

> On Fri, Jan 21, 2022 at 6:20 PM Colin Foster
> <colin.foster@in-advantage.com> wrote:
>>
>> On Fri, Jan 21, 2022 at 05:13:28PM -0800, Alexei Starovoitov wrote:
>> > On Fri, Jan 21, 2022 at 4:57 PM Colin Foster
>> > <colin.foster@in-advantage.com> wrote:
>> > >
>> > > Check for the existence of page pool params before dereferencing. This can
>> > > cause crashes in certain conditions.
>> >
>> > In what conditions?
>> > Out of tree driver?
>>
>> Hi Alexei,
>>
>> Thanks for the quick response.
>>
>> I'm actively working on a DSA driver that is currently out-of-tree, but
>> trying to get it into mainline. But I'm not convinced that's the
>> problem...
>>
>> I'm using a beagelebone black with the cpsw_new driver. There are two
>> tweaks to that driver: the default vlan port is 10 and 11 so there's no
>> conflict between cpsw_new and DSA, and the ndev->max_mtu / rx_packet_max
>> have been increased to 1600 to allow for DSA frames larger than the
>> standard MTU of 1500.
>>
>> My focus is on the DSA driver, but the crash happens as soon as I run
>> "ip link set eth0 up" which is invoking the cpsw_new driver. Therefore I
>> suspect that the issue is not directly related to the DSA section
>> (ocelot / felix, much of which uses code that is mainline)
>>
>> As I suggested, I haven't dug into what is going on around the
>> page_pool yet. If there is something that is pre-loading memory at 1500
>> byte intervals and I broke that, that's entirely on me.
>>
>> [ removes 1600 byte MTU patch and pool patch ]
>>
>> I can confirm it still crashes when I don't modify the MTU in the
>> cpsw_new driver... so that doesn't seem to be it. That crash log is
>> below.
>>
>>
>> # ip link set eth0 up
>> [ 18.074704] cpsw-switch 4a100000.switch: starting ndev. mode: dual_mac
>> [ 18.174286] SMSC LAN8710/LAN8720 4a101000.mdio:00: attached PHY driver (mii_bus:phy_addr=4a101000.mdio:00, irq=POLL)
>> [ 18.185458] 8<--- cut here ---
>> [ 18.188554] Unable to handle kernel paging request at virtual address c3104440
>> [ 18.195819] [c3104440] *pgd=8300041e(bad)
>> [ 18.199885] Internal error: Oops: 8000000d [#1] SMP ARM
>> [ 18.205148] Modules linked in:
>> [ 18.208233] CPU: 0 PID: 168 Comm: ip Not tainted 5.16.0-05302-g8bd405e6e8a0-dirty #265
>> [ 18.216201] Hardware name: Generic AM33XX (Flattened Device Tree)
>> [ 18.222328] PC is at 0xc3104440
>> [ 18.225500] LR is at __page_pool_alloc_pages_slow+0xbc/0x2e0
>> [ 18.231222] pc : [<c3104440>] lr : [<c0ee06c8>] psr: a00b0013
>> [ 18.237523] sp : c3104440 ip : 00000020 fp : c219e580
>> [ 18.242778] r10: c1a04d54 r9 : 00000000 r8 : 00000000
>> [ 18.248032] r7 : c36b9000 r6 : 00000000 r5 : c36b9084 r4 : 00000000
>> [ 18.254595] r3 : c07a399c r2 : 00000000 r1 : c325784c r0 : dfa48bc0
>> [ 18.261162] Flags: NzCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment none
>> [ 18.268343] Control: 10c5387d Table: 836f0019 DAC: 00000051
>> [ 18.274119] Register r0 information: non-slab/vmalloc memory
>> [ 18.279825] Register r1 information: non-slab/vmalloc memory
>> [ 18.285523] Register r2 information: NULL pointer
>> [ 18.290260] Register r3 information: non-slab/vmalloc memory
>> [ 18.295957] Register r4 information: NULL pointer
>> [ 18.300693] Register r5 information: slab kmalloc-1k start c36b9000 pointer offset 132 size 1024
>> [ 18.309569] Register r6 information: NULL pointer
>> [ 18.314306] Register r7 information: slab kmalloc-1k start c36b9000 pointer offset 0 size 1024
>> [ 18.322999] Register r8 information: NULL pointer
>> [ 18.327736] Register r9 information: NULL pointer
>> [ 18.332473] Register r10 information: non-slab/vmalloc memory
>> [ 18.338257] Register r11 information: slab kmalloc-4k start c219e000 pointer offset 1408 size 4096
>> [ 18.347301] Register r12 information: non-paged memory
>> [ 18.352475] Process ip (pid: 168, stack limit = 0x7eb0d4ab)
>> [ 18.358089] Stack: (0xc3104440 to 0xc3258000)
>> (too big a stack to show)
>>
>>
>> I can confirm that it crashes on net-next/master as well:
>> commit fe8152b38d3a, using the same DTB that defines the cpsw_new port
>> as the DSA master. Relevant DTS snippet from my in-development driver:
>>
>> +&spi0 {
>> + #address-cells = <1>;
>> + #size-cells = <0>;
>> + status = "okay";
>> +
>> + ocelot-chip@0 {
>> + compatible = "mscc,vsc7512_mfd_spi";
>> + spi-max-frequency = <2500000>;
>> + reg = <0>;
>> +
>> + ethernet-switch@0 {
>> + compatible = "mscc,vsc7512-ext-switch";
>> + ports {
>> + #address-cells = <1>;
>> + #size-cells = <0>;
>> +
>> + port@0 {
>> + reg = <0>;
>> + label = "cpu";
>> + status = "okay";
>> + ethernet = <&mac_sw>;
>> + phy-handle = <&sw_phy0>;
>> + phy-mode = "internal";
>> + };
>>
>>
>> I was hoping for an "oh, if a switch is set up in DSA the page_pool gets
>> set up this way" type scenario. I fully understand that might not be the
>> case, and the issue could be in something I'm doing incorrectly - it
>> certainly wouldn't be the first time.
>>
>> If this patch doesn't make sense I can look deeper. As mentioned, I'm
>> working to get this accepted upstream, so I'll have to figure it out one
>> way or another.
>
> With !pool tweak the patch makes sense.
>
> Toke, wdyt?

I don't really see how page_pool_set_pp_info() can be called with a NULL
'pool' pointer. There are only two callers:
__page_pool_alloc_page_order() and __page_pool_alloc_pages_slow(). And
both functions deref the pool pointer right before calling
page_pool_set_pp_info(), so I don't really see how this patch would
actually be a proper fix?

Looking a bit closer, actually the fault seems like it lies with the
driver; Colin, could you please check if the patch below fixes your
issue?

I'll go check all the other drivers as well and send a fix for all that
are affected...

-Toke

diff --git a/drivers/net/ethernet/ti/cpsw_priv.c b/drivers/net/ethernet/ti/cpsw_priv.c
index 3537502e5e8b..648c78ecf2a5 100644
--- a/drivers/net/ethernet/ti/cpsw_priv.c
+++ b/drivers/net/ethernet/ti/cpsw_priv.c
@@ -1146,7 +1146,7 @@ int cpsw_fill_rx_channels(struct cpsw_priv *priv)
static struct page_pool *cpsw_create_page_pool(struct cpsw_common *cpsw,
int size)
{
- struct page_pool_params pp_params;
+ struct page_pool_params pp_params = {};
struct page_pool *pool;

pp_params.order = 0;