Messages in this thread | | | From | Dmitry Vyukov <> | Date | Tue, 7 Nov 2017 12:09:19 +0100 | Subject | Re: [devkmsg_write] BUG: KASAN: slab-out-of-bounds in copyin+0xea/0x170 |
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On Tue, Nov 7, 2017 at 11:45 AM, Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> wrote: > Hello, > > On (11/07/17 17:39), Fengguang Wu wrote: >> [ 22.184920] Freeing unused kernel memory: 824K >> [ 22.199198] Freeing unused kernel memory: 1436K >> [ 22.228460] x86/mm: Checked W+X mappings: passed, no W+X pages found. >> [ 22.230474] rodata_test: all tests were successful >> [ 22.254830] ================================================================== >> [ 22.257125] BUG: KASAN: slab-out-of-bounds in copyin+0xea/0x170 >> [ 22.258648] Write of size 26 at addr ffff880013432540 by task init/1 >> [ 22.260272] >> [ 22.260860] CPU: 0 PID: 1 Comm: init Not tainted 4.14.0-rc8 #14 >> [ 22.262379] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014 >> [ 22.264441] Call Trace: >> [ 22.265206] dump_stack+0x5d/0x81 >> [ 22.266147] print_address_description+0xa7/0x280 >> [ 22.267369] ? copyin+0xea/0x170 >> [ 22.268282] ? copyin+0xea/0x170 >> [ 22.268990] kasan_report+0xd3/0x150 >> [ 22.269551] ? quarantine_reduce+0x1/0x1a0 >> [ 22.270177] ? copyin+0xea/0x170 >> [ 22.270703] copyin+0xea/0x170 >> [ 22.271202] _copy_from_iter_full+0x14f/0x4f0 >> [ 22.271857] ? __kmalloc+0x1ad/0x2e0 >> [ 22.272420] devkmsg_write+0xb9/0x1a0 >> [ 22.272999] new_sync_write+0xd8/0x130 >> [ 22.273579] vfs_write+0x174/0x2b0 >> [ 22.274113] SyS_write+0x50/0xc0 >> [ 22.274611] do_int80_syscall_32+0x7a/0x1b0 >> [ 22.275216] entry_INT80_compat+0x2d/0x40 > > at a glance I don't see anything suspicious in devkmsg_write(). > >> [ 22.276103] Allocated by task 1: >> [ 22.276597] kasan_kmalloc+0x61/0xf0 >> [ 22.277202] __kmalloc+0x1ad/0x2e0 >> [ 22.277720] devkmsg_write+0x76/0x1a0 >> [ 22.278268] new_sync_write+0xd8/0x130 >> [ 22.278826] vfs_write+0x174/0x2b0 >> [ 22.279342] SyS_write+0x50/0xc0 >> [ 22.279840] do_int80_syscall_32+0x7a/0x1b0 >> [ 22.280441] entry_INT80_compat+0x2d/0x40 > > devkmsg_write() does > > buf = kmalloc(len+1, GFP_KERNEL); > ... > kfree(buf); > > kasan reports that this kfree() is actually happening in unpack_to_rootfs(), > before we do copy_from_iter_full().
Please ignore the free stack. For slab-out-of-bound bugs the object is not actually freed and KASAN prints the free stack where it was freed before it was re-allocated as new object.
Can that len+1 overflow? Is it checked?
>> [ 22.281326] Freed by task 1: >> [ 22.281788] kasan_slab_free+0xac/0x180 >> [ 22.282354] kfree+0x105/0x310 >> [ 22.282837] unpack_to_rootfs+0x260/0x2a1 >> [ 22.283420] populate_rootfs+0x5d/0x86 >> [ 22.283977] do_one_initcall+0x3b/0x180 >> [ 22.284544] do_basic_setup+0xb4/0xd0 >> [ 22.285091] kernel_init_freeable+0x7b/0xed >> [ 22.285680] kernel_init+0xe/0x110 >> [ 22.286171] ret_from_fork+0x25/0x30 > > unpack_to_rootfs() does > > header_buf = kmalloc(110, GFP_KERNEL); > symlink_buf = kmalloc(PATH_MAX + N_ALIGN(PATH_MAX) + 1, GFP_KERNEL); > name_buf = kmalloc(N_ALIGN(PATH_MAX), GFP_KERNEL); > ... > kfree(name_buf); > kfree(symlink_buf); > kfree(header_buf); > > kasan reports that one of the pointers was allocated in devkmsg_write(). > what am I missing? > > -ss
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