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Merge branch 'asix-Improve-robustness'
Dean Jenkins says: ==================== asix: Improve robustness Please consider taking these patches to improve the robustness of the ASIX USB to Ethernet driver. Failures prompting an ASIX driver code review ============================================= On an ARM i.MX6 embedded platform some strange one-off and two-off failures were observed in and around the ASIX USB to Ethernet driver. This was observed on a highly modified kernel 3.14 with the ASIX driver containing back-ported changes from kernel.org up to kernel 4.8 approximately. a) A one-off failure in asix_rx_fixup_internal(): There was an occurrence of an attempt to write off the end of the netdev buffer which was trapped by skb_over_panic() in skb_put(). [20030.846440] skbuff: skb_over_panic: text:7f2271c0 len:120 put:60 head:8366ecc0 data:8366ed02 tail:0x8366ed7a end:0x8366ed40 dev:eth0 [20030.863007] Kernel BUG at 8044ce38 [verbose debug info unavailable] [20031.215345] Backtrace: [20031.217884] [<8044cde0>] (skb_panic) from [<8044d50c>] (skb_put+0x50/0x5c) [20031.227408] [<8044d4bc>] (skb_put) from [<7f2271c0>] (asix_rx_fixup_internal+0x1c4/0x23c [asix]) [20031.242024] [<7f226ffc>] (asix_rx_fixup_internal [asix]) from [<7f22724c>] (asix_rx_fixup_common+0x14/0x18 [asix]) [20031.260309] [<7f227238>] (asix_rx_fixup_common [asix]) from [<7f21f7d4>] (usbnet_bh+0x74/0x224 [usbnet]) [20031.269879] [<7f21f760>] (usbnet_bh [usbnet]) from [<8002f834>] (call_timer_fn+0xa4/0x1f0) [20031.283961] [<8002f790>] (call_timer_fn) from [<80030834>] (run_timer_softirq+0x230/0x2a8) [20031.302782] [<80030604>] (run_timer_softirq) from [<80028780>] (__do_softirq+0x15c/0x37c) [20031.321511] [<80028624>] (__do_softirq) from [<80028c38>] (irq_exit+0x8c/0xe8) [20031.339298] [<80028bac>] (irq_exit) from [<8000e9c8>] (handle_IRQ+0x8c/0xc8) [20031.350038] [<8000e93c>] (handle_IRQ) from [<800085c8>] (gic_handle_irq+0xb8/0xf8) [20031.365528] [<80008510>] (gic_handle_irq) from [<8050de80>] (__irq_svc+0x40/0x70) Analysis of the logic of the ASIX driver (containing backported changes from kernel.org up to kernel 4.8 approximately) suggested that the software could not trigger skb_over_panic(). The analysis of the kernel BUG() crash information suggested that the netdev buffer was written with 2 minimal 60 octet length Ethernet frames (ASIX hardware drops the 4 octet FCS field) and the 2nd Ethernet frame attempted to write off the end of the netdev buffer. Note that the netdev buffer should only contain 1 Ethernet frame so if an attempt to write 2 Ethernet frames into the buffer is made then that is wrong. However, the logic of the asix_rx_fixup_internal() only allows 1 Ethernet frame to be written into the netdev buffer. Potentially this failure was due to memory corruption because it was only seen once. b) Two-off failures in the NAPI layer's backlog queue: There were 2 crashes in the NAPI layer's backlog queue presumably after asix_rx_fixup_internal() called usbnet_skb_return(). [24097.273945] Unable to handle kernel NULL pointer dereference at virtual address 00000004 [24097.398944] PC is at process_backlog+0x80/0x16c [24097.569466] Backtrace: [24097.572007] [<8045ad98>] (process_backlog) from [<8045b64c>] (net_rx_action+0xcc/0x248) [24097.591631] [<8045b580>] (net_rx_action) from [<80028780>] (__do_softirq+0x15c/0x37c) [24097.610022] [<80028624>] (__do_softirq) from [<800289cc>] (run_ksoftirqd+0x2c/0x84) and [ 1059.828452] Unable to handle kernel NULL pointer dereference at virtual address 00000000 [ 1059.953715] PC is at process_backlog+0x84/0x16c [ 1060.140896] Backtrace: [ 1060.143434] [<8045ad98>] (process_backlog) from [<8045b64c>] (net_rx_action+0xcc/0x248) [ 1060.163075] [<8045b580>] (net_rx_action) from [<80028780>] (__do_softirq+0x15c/0x37c) [ 1060.181474] [<80028624>] (__do_softirq) from [<80028c38>] (irq_exit+0x8c/0xe8) [ 1060.199256] [<80028bac>] (irq_exit) from [<8000e9c8>] (handle_IRQ+0x8c/0xc8) [ 1060.210006] [<8000e93c>] (handle_IRQ) from [<800085c8>] (gic_handle_irq+0xb8/0xf8) [ 1060.225492] [<80008510>] (gic_handle_irq) from [<8050de80>] (__irq_svc+0x40/0x70) The embedded board was only using an ASIX USB to Ethernet adaptor eth0. Analysis suggested that the doubly-linked list pointers of the backlog queue had been corrupted because one of the link pointers was NULL. Potentially this failure was due to memory corruption because it was only seen twice. Results of the ASIX driver code review ====================================== During the code review some weaknesses were observed in the ASIX driver and the following patches have been created to improve the robustness. Brief overview of the patches ----------------------------- 1. asix: Add rx->ax_skb = NULL after usbnet_skb_return() The current ASIX driver sends the received Ethernet frame to the NAPI layer of the network stack via the call to usbnet_skb_return() in asix_rx_fixup_internal() but retains the rx->ax_skb pointer to the netdev buffer. The driver no longer needs the rx->ax_skb pointer at this point because the NAPI layer now has the Ethernet frame. This means that asix_rx_fixup_internal() must not use rx->ax_skb after the call to usbnet_skb_return() because it could corrupt the handling of the Ethernet frame within the network layer. Therefore, to remove the risk of erroneous usage of rx->ax_skb, set rx->ax_skb to NULL after the call to usbnet_skb_return(). This avoids potential erroneous freeing of rx->ax_skb and erroneous writing to the netdev buffer. If the software now somehow inappropriately reused rx->ax_skb, then a NULL pointer dereference of rx->ax_skb would occur which makes investigation easier. 2. asix: Ensure asix_rx_fixup_info members are all reset This patch creates reset_asix_rx_fixup_info() to allow all the asix_rx_fixup_info structure members to be consistently reset to initial conditions. Call reset_asix_rx_fixup_info() upon each detectable error condition so that the next URB is processed from a known state. Otherwise, there is a risk that some members of the asix_rx_fixup_info structure may be incorrect after an error occurred so potentially leading to a malfunction. 3. asix: Fix small memory leak in ax88772_unbind() This patch creates asix_rx_fixup_common_free() to allow the rx->ax_skb to be freed when necessary. asix_rx_fixup_common_free() is called from ax88772_unbind() before the parent private data structure is freed. Without this patch, there is a risk of a small netdev buffer memory leak each time ax88772_unbind() is called during the reception of an Ethernet frame that spans across 2 URBs. Testing ======= The patches have been sanity tested on a 64-bit Linux laptop running kernel 4.13-rc2 with the 3 patches applied on top. The ASIX USB to Adaptor used for testing was (output of lsusb): ID 0b95:772b ASIX Electronics Corp. AX88772B Test #1 ------- The test ran a flood ping test script which slowly incremented the ICMP Echo Request's payload from 0 to 5000 octets. This eventually causes IPv4 fragmentation to occur which causes Ethernet frames to be sent very close to each other so increases the probability that an Ethernet frame will span 2 URBs. The test showed that all pings were successful. The test took about 15 minutes to complete. Test #2 ------- A script was run on the laptop to periodically run ifdown and ifup every second so that the ASIX USB to Adaptor was up for 1 second and down for 1 second. From a Linux PC connected to the laptop, the following ping command was used ping -f -s 5000 <ip address of laptop> The large ICMP payload causes IPv4 fragmentation resulting in multiple Ethernet frames per original IP packet. Kernel debug within the ASIX driver was enabled to see whether any ASIX errors were generated. The test was run for about 24 hours and no ASIX errors were seen. Patches ======= The 3 patches have been rebased off the net-next repo master branch with HEAD fbbeefd net: fec: Allow reception of frames bigger than 1522 bytes ==================== Signed-off-by: David S. Miller <davem@davemloft.net>
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