Fri, 25 Sep 2020 01:57:16 -0700
> syzbot found the following issue on:
>
> HEAD commit: 171d4ff7 Merge tag 'mmc-v5.9-rc4-2' of git://git.kernel.or..
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=17d457b5900000
> kernel config: https://syzkaller.appspot.com/x/.config?x=5f4c828c9e3cef97
> dashboard link: https://syzkaller.appspot.com/bug?extid=2d0585e5efcd43d113c2
> compiler: gcc (GCC) 10.1.0-syz 20200507
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=16a33ad3900000
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: [email protected]
>
> ==================================================================
> BUG: KASAN: use-after-free in memcpy include/linux/string.h:406 [inline]
> BUG: KASAN: use-after-free in fscache_set_key fs/fscache/cookie.c:93 [inline]
> BUG: KASAN: use-after-free in fscache_alloc_cookie+0xff/0x730
> fs/fscache/cookie.c:153
> Read of size 10 at addr ffff8880a6c28200 by task kworker/1:6/8760
>
> CPU: 1 PID: 8760 Comm: kworker/1:6 Not tainted 5.9.0-rc6-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> Workqueue: afs afs_manage_cell
> Call Trace:
> __dump_stack lib/dump_stack.c:77 [inline]
> dump_stack+0x198/0x1fd lib/dump_stack.c:118
> print_address_description.constprop.0.cold+0xae/0x497 mm/kasan/report.c:383
> __kasan_report mm/kasan/report.c:513 [inline]
> kasan_report.cold+0x1f/0x37 mm/kasan/report.c:530
> check_memory_region_inline mm/kasan/generic.c:186 [inline]
> check_memory_region+0x13d/0x180 mm/kasan/generic.c:192
> memcpy+0x20/0x60 mm/kasan/common.c:105
> memcpy include/linux/string.h:406 [inline]
> fscache_set_key fs/fscache/cookie.c:93 [inline]
> fscache_alloc_cookie+0xff/0x730 fs/fscache/cookie.c:153
> __fscache_acquire_cookie+0x16c/0x610 fs/fscache/cookie.c:288
> fscache_acquire_cookie include/linux/fscache.h:334 [inline]
> afs_activate_cell fs/afs/cell.c:609 [inline]
> afs_manage_cell+0x4fa/0x11c0 fs/afs/cell.c:697
> process_one_work+0x94c/0x1670 kernel/workqueue.c:2269
> worker_thread+0x64c/0x1120 kernel/workqueue.c:2415
> kthread+0x3b5/0x4a0 kernel/kthread.c:292
> ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294
>
> Allocated by task 10197:
> kasan_save_stack+0x1b/0x40 mm/kasan/common.c:48
> kasan_set_track mm/kasan/common.c:56 [inline]
> __kasan_kmalloc.constprop.0+0xbf/0xd0 mm/kasan/common.c:461
> __do_kmalloc mm/slab.c:3655 [inline]
> __kmalloc+0x1b0/0x360 mm/slab.c:3664
> kmalloc include/linux/slab.h:559 [inline]
> afs_alloc_cell fs/afs/cell.c:157 [inline]
> afs_lookup_cell+0x5e9/0x1440 fs/afs/cell.c:262
> afs_parse_source fs/afs/super.c:290 [inline]
> afs_parse_param+0x404/0x8c0 fs/afs/super.c:326
> vfs_parse_fs_param fs/fs_context.c:117 [inline]
> vfs_parse_fs_param+0x203/0x550 fs/fs_context.c:98
> vfs_parse_fs_string+0xe6/0x150 fs/fs_context.c:161
> generic_parse_monolithic+0x16f/0x1f0 fs/fs_context.c:201
> do_new_mount fs/namespace.c:2871 [inline]
> path_mount+0x133f/0x20a0 fs/namespace.c:3192
> do_mount fs/namespace.c:3205 [inline]
> __do_sys_mount fs/namespace.c:3413 [inline]
> __se_sys_mount fs/namespace.c:3390 [inline]
> __x64_sys_mount+0x27f/0x300 fs/namespace.c:3390
> do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
> entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
> Freed by task 16:
> kasan_save_stack+0x1b/0x40 mm/kasan/common.c:48
> kasan_set_track+0x1c/0x30 mm/kasan/common.c:56
> kasan_set_free_info+0x1b/0x30 mm/kasan/generic.c:355
> __kasan_slab_free+0xd8/0x120 mm/kasan/common.c:422
> __cache_free mm/slab.c:3418 [inline]
> kfree+0x10e/0x2b0 mm/slab.c:3756
> afs_cell_destroy+0x1b0/0x240 fs/afs/cell.c:500
> rcu_do_batch kernel/rcu/tree.c:2428 [inline]
> rcu_core+0x5ca/0x1130 kernel/rcu/tree.c:2656
> __do_softirq+0x1f8/0xb23 kernel/softirq.c:298
>
> The buggy address belongs to the object at ffff8880a6c28200
> which belongs to the cache kmalloc-32 of size 32
> The buggy address is located 0 bytes inside of
> 32-byte region [ffff8880a6c28200, ffff8880a6c28220)
> The buggy address belongs to the page:
> page:00000000c2f50dc7 refcount:1 mapcount:0 mapping:0000000000000000
> index:0xffff8880a6c28fc1 pfn:0xa6c28
> flags: 0xfffe0000000200(slab)
> raw: 00fffe0000000200 ffffea00028969c8 ffffea00025ca748 ffff8880aa040100
> raw: ffff8880a6c28fc1 ffff8880a6c28000 000000010000003f 0000000000000000
> page dumped because: kasan: bad access detected
>
> Memory state around the buggy address:
> ffff8880a6c28100: fa fb fb fb fc fc fc fc fa fb fb fb fc fc fc fc
> ffff8880a6c28180: fa fb fb fb fc fc fc fc fa fb fb fb fc fc fc fc
> >ffff8880a6c28200: fa fb fb fb fc fc fc fc fa fb fb fb fc fc fc fc
> ^
> ffff8880a6c28280: 00 00 00 00 fc fc fc fc 00 fc fc fc fc fc fc fc
> ffff8880a6c28300: fa fb fb fb fc fc fc fc fa fb fb fb fc fc fc fc
> ==================================================================
Flush the manager work before releasing cell's resources to avoid uaf.
To that end, add the AFS_CELL_DESTROYING cell state to infom the kworker
that there's no more job to do.
--- a/fs/afs/internal.h
+++ b/fs/afs/internal.h
@@ -344,6 +344,7 @@ enum afs_cell_state {
AFS_CELL_DEACTIVATING,
AFS_CELL_INACTIVE,
AFS_CELL_FAILED,
+ AFS_CELL_DESTROYING,
};
/*
--- a/fs/afs/cell.c
+++ b/fs/afs/cell.c
@@ -493,6 +493,7 @@ static void afs_cell_destroy(struct rcu_
ASSERTCMP(atomic_read(&cell->usage), ==, 0);
+ flush_work(&cell->manager);
afs_put_volume(cell->net, cell->root_volume,
afs_volume_trace_put_cell_root);
afs_put_vlserverlist(cell->net, rcu_access_pointer(cell->vl_servers));
afs_put_cell(cell->net, cell->alias_of);
@@ -672,13 +673,17 @@ static void afs_manage_cell(struct work_
again:
_debug("state %u", cell->state);
switch (cell->state) {
+ case AFS_CELL_DESTROYING:
+ return;
case AFS_CELL_INACTIVE:
case AFS_CELL_FAILED:
write_seqlock(&net->cells_lock);
usage = 1;
deleted = atomic_try_cmpxchg_relaxed(&cell->usage, &usage, 0);
- if (deleted)
+ if (deleted) {
rb_erase(&cell->net_node, &net->cells);
+ cell->state = AFS_CELL_DESTROYING;
+ }
write_sequnlock(&net->cells_lock);
if (deleted)
goto final_destruction;
--
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