From: Evan Lambert The function io_buffer_register_bvec() calculates the allocation size for the io_mapped_ubuf based on blk_rq_nr_phys_segments(rq). This function calculates the number of scatter-gather elements after megine physically contiguous pages. However, the subsequent loop uses rq_for_each_bvec() to populate the array, which iterates over every individual bio_vec in the request, regardless of physical contiguity. If a request has multiple bio_vec entries that are physically contiguous, blk_rq_nr_phys_segments() returns a value smaller than the total number of bio_vecs. This leads to a slab-out-of-bounds write. The path is reachable from userspace via the ublk driver when a server issues a UBLK_IO_REGISTER_IO_BUF command. This requires the UBLK_F_SUPPORT_ZERO_COPY flag which is protected by CAP_NET_ADMIN. Fix this by calculating the total number of bio_vecs by iterating over the request's bios and summing their bi_vcnt. KASAN report: [18:01:50] BUG: KASAN: slab-out-of-bounds in io_buffer_register_bvec+0x813/0xb80 [18:01:50] Write of size 8 at addr ffff88800223b238 by task kunit_try_catch/27 [18:01:50] [18:01:50] CPU: 0 UID: 0 PID: 27 Comm: kunit_try_catch Tainted: G N 6.19.0-rc1-g346af1a0c65a-dirty #44 PREEMPT(none) [18:01:50] Tainted: [N]=TEST [18:01:50] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 0.1 11/11/2019 [18:01:50] Call Trace: [18:01:50] [18:01:50] dump_stack_lvl+0x4d/0x70 [18:01:50] print_report+0x151/0x4c0 [18:01:50] ? __pfx__raw_spin_lock_irqsave+0x10/0x10 [18:01:50] ? io_buffer_register_bvec+0x813/0xb80 [18:01:50] kasan_report+0xec/0x120 [18:01:50] ? io_buffer_register_bvec+0x813/0xb80 [18:01:50] io_buffer_register_bvec+0x813/0xb80 [18:01:50] io_buffer_register_bvec_overflow_test+0x4e6/0x9b0 [18:01:50] ? __pfx_io_buffer_register_bvec_overflow_test+0x10/0x10 [18:01:50] ? __pfx_pick_next_task_fair+0x10/0x10 [18:01:50] ? _raw_spin_lock+0x7e/0xd0 [18:01:50] ? finish_task_switch.isra.0+0x19a/0x650 [18:01:50] ? __pfx_read_tsc+0x10/0x10 [18:01:50] ? ktime_get_ts64+0x79/0x240 [18:01:50] kunit_try_run_case+0x19b/0x2c0 [18:01:50] ? __pfx_kunit_try_run_case+0x10/0x10 [18:01:50] ? __pfx_kunit_generic_run_threadfn_adapter+0x10/0x10 [18:01:50] kunit_generic_run_threadfn_adapter+0x80/0xf0 [18:01:50] kthread+0x323/0x670 [18:01:50] ? __pfx_kthread+0x10/0x10 [18:01:50] ? __pfx__raw_spin_lock_irq+0x10/0x10 [18:01:50] ? __pfx_kthread+0x10/0x10 [18:01:50] ret_from_fork+0x329/0x420 [18:01:50] ? __pfx_ret_from_fork+0x10/0x10 [18:01:50] ? __switch_to+0xa0f/0xd40 [18:01:50] ? __pfx_kthread+0x10/0x10 [18:01:50] ret_from_fork_asm+0x1a/0x30 [18:01:50] [18:01:50] [18:01:50] Allocated by task 27: [18:01:50] kasan_save_stack+0x30/0x50 [18:01:50] kasan_save_track+0x14/0x30 [18:01:50] __kasan_kmalloc+0x7f/0x90 [18:01:50] io_cache_alloc_new+0x35/0xc0 [18:01:50] io_buffer_register_bvec+0x196/0xb80 [18:01:50] io_buffer_register_bvec_overflow_test+0x4e6/0x9b0 [18:01:50] kunit_try_run_case+0x19b/0x2c0 [18:01:50] kunit_generic_run_threadfn_adapter+0x80/0xf0 [18:01:50] kthread+0x323/0x670 [18:01:50] ret_from_fork+0x329/0x420 [18:01:50] ret_from_fork_asm+0x1a/0x30 [18:01:50] [18:01:50] The buggy address belongs to the object at ffff88800223b000 [18:01:50] which belongs to the cache kmalloc-1k of size 1024 [18:01:50] The buggy address is located 0 bytes to the right of [18:01:50] allocated 568-byte region [ffff88800223b000, ffff88800223b238) [18:01:50] [18:01:50] The buggy address belongs to the physical page: [18:01:50] page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x2238 [18:01:50] head: order:2 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0 [18:01:50] flags: 0x4000000000000040(head|zone=1) [18:01:50] page_type: f5(slab) [18:01:50] raw: 4000000000000040 ffff888001041dc0 dead000000000122 0000000000000000 [18:01:50] raw: 0000000000000000 0000000080080008 00000000f5000000 0000000000000000 [18:01:50] head: 4000000000000040 ffff888001041dc0 dead000000000122 0000000000000000 [18:01:50] head: 0000000000000000 0000000080080008 00000000f5000000 0000000000000000 [18:01:50] head: 4000000000000002 ffffea0000088e01 00000000ffffffff 00000000ffffffff [18:01:50] head: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000 [18:01:50] page dumped because: kasan: bad access detected [18:01:50] [18:01:50] Memory state around the buggy address: [18:01:50] ffff88800223b100: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 [18:01:50] ffff88800223b180: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 [18:01:50] >ffff88800223b200: 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc [18:01:50] ^ [18:01:50] ffff88800223b280: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc [18:01:50] ffff88800223b300: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc [18:01:50] ================================================================== [18:01:50] Disabling lock debugging due to kernel taint Fixes: 27cb27b6d5ea ("io_uring: add support for kernel registered bvecs") Signed-off-by: Evan Lambert --- io_uring/rsrc.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c index a63474b331bf..7602b71543e0 100644 --- a/io_uring/rsrc.c +++ b/io_uring/rsrc.c @@ -946,6 +946,7 @@ int io_buffer_register_bvec(struct io_uring_cmd *cmd, struct request *rq, struct io_mapped_ubuf *imu; struct io_rsrc_node *node; struct bio_vec bv; + struct bio *bio; unsigned int nr_bvecs = 0; int ret = 0; @@ -967,11 +968,10 @@ int io_buffer_register_bvec(struct io_uring_cmd *cmd, struct request *rq, goto unlock; } - /* - * blk_rq_nr_phys_segments() may overestimate the number of bvecs - * but avoids needing to iterate over the bvecs - */ - imu = io_alloc_imu(ctx, blk_rq_nr_phys_segments(rq)); + __rq_for_each_bio(bio, rq) + nr_bvecs += bio->bi_vcnt; + + imu = io_alloc_imu(ctx, nr_bvecs); if (!imu) { kfree(node); ret = -ENOMEM; @@ -988,6 +988,7 @@ int io_buffer_register_bvec(struct io_uring_cmd *cmd, struct request *rq, imu->is_kbuf = true; imu->dir = 1 << rq_data_dir(rq); + nr_bvecs = 0; rq_for_each_bvec(bv, rq, rq_iter) imu->bvec[nr_bvecs++] = bv; imu->nr_bvecs = nr_bvecs; -- 2.52.0