Reading or writing a link state sysfs attribute after the upstream bridge's pcie_link_state has been freed triggers a NULL pointer dereference. This was first seen on a 6.12 based kernel by userspace stress testing a PCIe endpoint on an RK3588 EVB1 (Intel I350 dual-port NIC behind the root port). The same NULL pointer dereference exists in upstream and can be reproduced reliably on: # lspci 00:00.0 PCI bridge: Rockchip Electronics Co., Ltd RK3588 (rev 01) 01:00.0 Ethernet controller: Intel Corporation I350 Gigabit Network Connection (rev 01) 01:00.1 Ethernet controller: Intel Corporation I350 Gigabit Network Connection (rev 01) by running: echo 1 > /sys/bus/pci/devices/0000:01:00.0/remove cat /sys/bus/pci/devices/0000:01:00.1/link/l1_aspm Unable to handle kernel NULL pointer dereference at virtual address 0000000000000030 Mem abort info: ESR = 0x0000000096000004 EC = 0x25: DABT (current EL), IL = 32 bits SET = 0, FnV = 0 EA = 0, S1PTW = 0 FSC = 0x04: level 0 translation fault Data abort info: ISV = 0, ISS = 0x00000004, ISS2 = 0x00000000 CM = 0, WnR = 0, TnD = 0, TagAccess = 0 GCS = 0, Overlay = 0, DirtyBit = 0 user pgtable: 4k pages, 48-bit VAs, pgdp=0000000106959000 [0000000000000030] pgd=0000000000000000, p4d=0000000000000000 Internal error: Oops: 0000000096000004 [#1] SMP Modules linked in: CPU: 3 UID: 0 PID: 646 Comm: cat Not tainted 7.3.0-rc6-next-20261007-00007-gf2fe32674ebe-dirty #134 PREEMPT(full) Hardware name: Rockchip RK3588 EVB1 V10 Board (DT) pstate: 40400009 (nZcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--) pc : l1_aspm_show+0x64/0x88 lr : dev_attr_show+0x24/0x68 sp : ffff800086f9bbf0 x29: ffff800086f9bbf0 x28: ffff0001036c0000 x27: 0000000000000000 x26: 0000000000000000 x25: 000000007ffff001 x24: 0000000000000001 x23: ffff800081781630 x22: ffff0001008d3c00 x21: ffff0001053b9000 x20: ffff0001020880d0 x19: ffff800082441c28 x18: 0000000000000000 x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000000 x14: 0000000000000000 x13: 0000000000000000 x12: 00000000ffffe000 x11: ffff0001053b9000 x10: 0000000000c00010 x9 : 0000000000000070 x8 : 0000000000000000 x7 : 0000000000000000 x6 : 000000000000003f x5 : 0000000000000040 x4 : 0000000000000000 x3 : 0000000000000004 x2 : ffff0001053b9000 x1 : ffff800082441c28 x0 : ffff0001053b9000 Call trace: l1_aspm_show+0x64/0x88 (P) dev_attr_show+0x24/0x68 sysfs_kf_seq_show+0xb8/0x138 kernfs_seq_show+0x2c/0x38 seq_read_iter+0x120/0x3e0 kernfs_fop_read_iter+0x60/0x188 vfs_read+0x200/0x2b8 ksys_read+0x74/0xe8 __arm64_sys_read+0x1c/0x28 invoke_syscall+0x44/0xec el0_svc_common+0x8c/0xd8 do_el0_svc+0x1c/0x28 el0_svc+0x3c/0x98 el0t_64_sync_handler+0x84/0x12c el0t_64_sync+0x198/0x19c Code: aa1f03e8 d503233f a9bf7bfd 910003fd (b9403108) ---[ end trace 0000000000000000 ]--- Kernel panic - not syncing: Oops: Fatal exception SMP: stopping secondary CPUs Kernel Offset: disabled CPU features: 0x0,70000000,0070002a,01180a42,0800e20b Memory Limit: none ---[ end Kernel panic - not syncing: Oops: Fatal exception ]--- The sysfs attributes are created for every device below the link, but the link state is freed by pcie_aspm_exit_link_state() when function 0 of the downstream component is removed. A sibling function or a sysfs reader still holding a reference can then call into the show/store callbacks while pcie_aspm_get_link() returns NULL. aspm_attr_show_common(), aspm_attr_store_common(), clkpm_show() and clkpm_store() all dereference the link pointer unconditionally. Add the missing NULL checks, mirroring pcie_aspm_enabled(), and return -ENODEV. Cc: stable@vger.kernel.org Fixes: 72ea91afbfb0 ("PCI/ASPM: Add sysfs attributes for controlling ASPM link states") Signed-off-by: Shawn Lin --- drivers/pci/pcie/aspm.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c index f8e6497..0e0ba0e6 100644 --- a/drivers/pci/pcie/aspm.c +++ b/drivers/pci/pcie/aspm.c @@ -1777,6 +1777,9 @@ static ssize_t aspm_attr_show_common(struct device *dev, struct pci_dev *pdev = to_pci_dev(dev); struct pcie_link_state *link = pcie_aspm_get_link(pdev); + if (!link) + return -ENODEV; + return sysfs_emit(buf, "%d\n", (link->aspm_enabled & state) ? 1 : 0); } @@ -1788,6 +1791,9 @@ static ssize_t aspm_attr_store_common(struct device *dev, struct pcie_link_state *link = pcie_aspm_get_link(pdev); bool state_enable; + if (!link) + return -ENODEV; + if (kstrtobool(buf, &state_enable) < 0) return -EINVAL; @@ -1836,6 +1842,9 @@ static ssize_t clkpm_show(struct device *dev, struct pci_dev *pdev = to_pci_dev(dev); struct pcie_link_state *link = pcie_aspm_get_link(pdev); + if (!link) + return -ENODEV; + return sysfs_emit(buf, "%d\n", link->clkpm_enabled); } @@ -1847,6 +1856,9 @@ static ssize_t clkpm_store(struct device *dev, struct pcie_link_state *link = pcie_aspm_get_link(pdev); bool state_enable; + if (!link) + return -ENODEV; + if (kstrtobool(buf, &state_enable) < 0) return -EINVAL; -- 2.7.4