On Fri, Jul 21, 2023 at 11:56 AM Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > > On Fri, Jul 21, 2023 at 11:23:10AM -0700, Khazhy Kumykov wrote: > > On Fri, Jul 21, 2023 at 11:10 AM Khazhy Kumykov <khazhy@xxxxxxxxxx> wrote: > > > > > > On Mon, Jun 19, 2023 at 7:56 PM syzbot > > > <syzbot+18996170f8096c6174d0@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote: > > > > > > > > Hello, > > > > > > > > syzbot found the following issue on: > > > > > > > > HEAD commit: 40f71e7cd3c6 Merge tag 'net-6.4-rc7' of git://git.kernel.o.. > > > > git tree: upstream > > > > console+strace: https://syzkaller.appspot.com/x/log.txt?x=1581445b280000 > > > > kernel config: https://syzkaller.appspot.com/x/.config?x=ac246111fb601aec > > > > dashboard link: https://syzkaller.appspot.com/bug?extid=18996170f8096c6174d0 > > > > compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2 > > > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=15d23487280000 > > > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16613ed3280000 > > > > > > > > Downloadable assets: > > > > disk image: https://storage.googleapis.com/syzbot-assets/30922ad38c58/disk-40f71e7c.raw.xz > > > > vmlinux: https://storage.googleapis.com/syzbot-assets/3bd12e7503b8/vmlinux-40f71e7c.xz > > > > kernel image: https://storage.googleapis.com/syzbot-assets/1dcd340b18d4/bzImage-40f71e7c.xz > > > > > > > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > > > > Reported-by: syzbot+18996170f8096c6174d0@xxxxxxxxxxxxxxxxxxxxxxxxx > > > > > > > > ================================================================== > > > > BUG: KASAN: slab-out-of-bounds in read_descriptors+0x263/0x280 drivers/usb/core/sysfs.c:883 > > > > Read of size 8 at addr ffff88801e78b8c8 by task udevd/5011 > > > > > > > > CPU: 0 PID: 5011 Comm: udevd Not tainted 6.4.0-rc6-syzkaller-00195-g40f71e7cd3c6 #0 > > > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/27/2023 > > > > Call Trace: > > > > <TASK> > > > > __dump_stack lib/dump_stack.c:88 [inline] > > > > dump_stack_lvl+0xd9/0x150 lib/dump_stack.c:106 > > > > print_address_description.constprop.0+0x2c/0x3c0 mm/kasan/report.c:351 > > > > print_report mm/kasan/report.c:462 [inline] > > > > kasan_report+0x11c/0x130 mm/kasan/report.c:572 > > > > > > "src = udev->rawdescriptors[cfgno]" (so, just reading rawdescriptors) > > > > > > > read_descriptors+0x263/0x280 drivers/usb/core/sysfs.c:883 > > > > sysfs_kf_bin_read+0x19a/0x270 fs/sysfs/file.c:97 > > > > kernfs_file_read_iter fs/kernfs/file.c:251 [inline] > > > > kernfs_fop_read_iter+0x387/0x690 fs/kernfs/file.c:280 > > > > call_read_iter include/linux/fs.h:1862 [inline] > > > > new_sync_read fs/read_write.c:389 [inline] > > > > vfs_read+0x4b1/0x8a0 fs/read_write.c:470 > > > > ksys_read+0x12b/0x250 fs/read_write.c:613 > > > > do_syscall_x64 arch/x86/entry/common.c:50 [inline] > > > > do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80 > > > > entry_SYSCALL_64_after_hwframe+0x63/0xcd > > > > RIP: 0033:0x7f07c7916b6a > > > > Code: 00 3d 00 00 41 00 75 0d 50 48 8d 3d 2d 08 0a 00 e8 ea 7d 01 00 31 c0 e9 07 ff ff ff 64 8b 04 25 18 00 00 00 85 c0 75 1b 0f 05 <48> 3d 00 f0 ff ff 76 6c 48 8b 15 8f a2 0d 00 f7 d8 64 89 02 48 83 > > > > RSP: 002b:00007ffdf34973d8 EFLAGS: 00000246 ORIG_RAX: 0000000000000000 > > > > RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f07c7916b6a > > > > RDX: 0000000000010011 RSI: 00007ffdf3497407 RDI: 0000000000000008 > > > > RBP: 0000000000000008 R08: 0000000000000003 R09: f4f13e10193fbafe > > > > R10: 0000000000000000 R11: 0000000000000246 R12: 000055be37470e10 > > > > R13: 00007ffdf34a7ae8 R14: 00007ffdf34a8138 R15: 00007ffdf3497407 > > > > </TASK> > > > > > > > > Allocated by task 758: > > > > kasan_save_stack+0x22/0x40 mm/kasan/common.c:45 > > > > kasan_set_track+0x25/0x30 mm/kasan/common.c:52 > > > > ____kasan_kmalloc mm/kasan/common.c:374 [inline] > > > > ____kasan_kmalloc mm/kasan/common.c:333 [inline] > > > > __kasan_kmalloc+0xa2/0xb0 mm/kasan/common.c:383 > > > > kasan_kmalloc include/linux/kasan.h:196 [inline] > > > > __do_kmalloc_node mm/slab_common.c:966 [inline] > > > > __kmalloc+0x5e/0x190 mm/slab_common.c:979 > > > > kmalloc include/linux/slab.h:563 [inline] > > > > kzalloc include/linux/slab.h:680 [inline] > > > > > > kzmalloc(length) -> this length derived from dev->descriptor.bNumConfigurations > > > > > > The corresponding kfree is in usb_destroy_configuration (makes sense) > > > - we also set rawdescriptors to NULL here. If this race was happening, > > > I'd also expect some sort of null deref report... > > > > > > Stumbled upon https://lore.kernel.org/all/1599201467-11000-1-git-send-email-prime.zeng@xxxxxxxxxxxxx/T/, > > > which suggests that we can, instead, race with a descriptor change, > > > which sounds plausible - descriptor changes, bNumConfigurations no > > > longer lines up with our kmalloc... so we may run past the end of it. > > Ah yeah, the syzbot C repro does something like this, it has a virtual > > usb and keeps changing the descs -> which may end up calling > > hub_port_connect_change() > > Yes, that sounds right. > > The problem-causing commit is 45bf39f8df7f ("USB: core: Don't hold > device lock while reading the "descriptors" sysfs file"). When writing > the commit message I only considered changes to the rawdescriptors; it > didn't occur to me that the device descriptor might also change, which > would be just as dangerous. > > > > Looking at hub_port_connect_change(), we seem to read directly into > > > udev->descriptor, check if it changed, and if it did, set > > > udev->descriptor back to the old one...? If we have an ongoing sysfs > > > read, which directly touches udev->descriptor, there might be > > > trouble... > > > > > > I see this is called in both hub_port_connect_change() and > > > usb_reset_and_verify_device()... which both seem to lock the port_dev? > > > ("port_dev->status_lock"). This looks like a different lock than > > > usb_lock_device_interruptible would grab, maybe the code has changed > > > since that was reported in 2020. But it seems to suggest we want to > > > grab this lock in sysfs to safely read from udev->descriptor. > > > > > > (I'm not clear on when the sysfs gets added/removed, since it happens > > > in usb_bus_notify()..., the above two functions that touch > > > udev->descriptor don't look like they send the > > > BUS_NOTIFY_ADD/DEL_DEVICE to me, so the race seems plausible) > > > > Ah yeah - in hub_port_connect_change() we call hub_port_connect() if > > the descriptor changed, which notifies us of device remove *after* we > > already directly messed with udev->descriptor for a potentially live > > device. > > > > I do see there's several sysfs files that directly read > > udev->descriptor with no locking - should these all need to grab the > > port_dev->status_lock? > > I suppose some of them should. (For others, the caller will already > hold the device lock.) > > On the other hand, it would almost certainly be simpler if > hub_port_connect_change() and the other places calling > usb_get_device_descriptor() would read into a temporary buffer instead > of directly into udev->descriptor. Do you think the problem could be > solved this way? It would be cleaner in the end. Simpler... It'll probably be cleaner in the end, but we're snapshotting and resetting udev->descriptor several call frames above where we're calling usb_get_device_descriptor in the case of usb_reset_and_verify_device().. For hub_port_connect_change() it should be straightforward - use the on-stack descriptor as the buf for usb_get_descriptor(), and bail out like we do already. For usb_reset_and_verify_device... we're calling hub_port_init, which is directly modifying a bunch of the usb struct, fetches the descriptor, validates it, and we rely on the return here to decide whether or not to simulate a disconnect... I'd personally lean to reverting 45bf39f8df7f, but I'm not that familiar with the code here. :) > > Alan Stern
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