Submitting SQEs through an io_uring BPF loop can trigger a NULL pointer dereference in io_submit_sqes(), as shown by the following arm64 report: [ 2049.380301] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000 [ 2049.388788] pc : io_submit_sqes+0x48/0x6c4 [ 2049.389153] lr : bpf_io_uring_submit_sqes+0x10/0x1c [ 2049.396310] Call trace: [ 2049.396531] io_submit_sqes+0x48/0x6c4 (P) [ 2049.396893] bpf_io_uring_submit_sqes+0x10/0x1c [ 2049.397293] bpf_prog_1a2a95cb199202b5+0x3c/0x68 [ 2049.397699] bpf__io_uring_bpf_ops_loop_step+0x5c/0x94 [ 2049.398149] io_run_loop+0x70/0x2e4 [ 2049.398461] __arm64_sys_io_uring_enter+0xf0/0x710 [ 2049.398882] invoke_syscall+0x54/0x10c [ 2049.399414] el0_svc_common.constprop.0+0x40/0xe0 [ 2049.399829] do_el0_svc+0x1c/0x28 [ 2049.400125] el0_svc+0x38/0x1d0 [ 2049.400409] el0t_64_sync_handler+0xa0/0xe4 [ 2049.400779] el0t_64_sync+0x198/0x19c io_uring_enter() dispatches to io_run_loop() before reaching the normal submission path's io_uring_add_tctx_node() call. The loop only checks whether the caller is allowed to run task work; it does not initialize current->io_uring or associate the task with the ring. A BPF call to bpf_io_uring_submit_sqes() then reaches io_get_task_refs(), which assumes that current->io_uring is valid. A ring created with IORING_SETUP_R_DISABLED, IORING_SETUP_SINGLE_ISSUER and IORING_SETUP_DEFER_TASKRUN can be enabled by a different task that has never used io_uring. Enabling the ring makes that task the submitter without allocating its io_uring task context. Its first BPF-driven submission of a pending SQE can therefore cause a kernel Oops. Call io_uring_add_tctx_node() in io_run_loop() before invoking the loop and propagate any initialization error. Do this before acquiring uring_lock, since task context setup may acquire the same mutex. This also establishes the task-to-ring association used for cancellation. Fixes: 033af2b3eb19 ("io_uring: introduce callback driven main loop") Signed-off-by: Yao Kai --- io_uring/loop.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/io_uring/loop.c b/io_uring/loop.c index bbbb6ef14e6a..3d472b7827fa 100644 --- a/io_uring/loop.c +++ b/io_uring/loop.c @@ -2,6 +2,7 @@ #include "io_uring.h" #include "wait.h" #include "loop.h" +#include "tctx.h" static inline int io_loop_nr_cqes(const struct io_ring_ctx *ctx, const struct iou_loop_params *lp) @@ -81,6 +82,10 @@ int io_run_loop(struct io_ring_ctx *ctx) { int ret; + ret = io_uring_add_tctx_node(ctx); + if (unlikely(ret)) + return ret; + if (!io_allowed_run_tw(ctx)) return -EEXIST; -- 2.43.0