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Writing to the netdevsim debugfs file "netdevsim/netdevsimN/fib/nexthop_bucket_activity" enters nsim_nexthop_bucket_activity_write(), which looks up a nexthop in data->nexthop_ht under rtnl_lock(). If a network namespace teardown, devlink reload or device deletion runs concurrently, nsim_fib_destroy() frees that rhashtable (and the surrounding nsim_fib_data) while the write is still in flight, leading to a slab-use-after-free: BUG: KASAN: slab-use-after-free in nsim_nexthop_bucket_activity_write+0xb9e/0xdf0 Read of size 4 at addr ff1100001a379808 by task syz.0.11967/27894 CPU: 0 UID: 0 PID: 27894 Comm: syz.0.11967 Not tainted 7.1.0-rc4-gf6f1bfc1980a #4 Call Trace: nsim_nexthop_bucket_activity_write+0xb9e/0xdf0 full_proxy_write+0x135/0x1a0 vfs_write+0x2e2/0x1040 ksys_write+0x146/0x270 __x64_sys_write+0x76/0xb0 do_syscall_64+0xb9/0x5b0 entry_SYSCALL_64_after_hwframe+0x74/0x7c Allocated by task 15957: rhashtable_init_noprof+0x3ec/0x860 nsim_fib_create+0x371/0xca0 nsim_drv_probe+0xd60/0x15c0 ... new_device_store+0x425/0x7f0 Freed by task 24: rhashtable_free_and_destroy+0x10d/0x620 nsim_fib_destroy+0xc9/0x1c0 nsim_dev_reload_destroy+0x1e7/0x530 nsim_dev_reload_down+0x6b/0xd0 devlink_reload+0x1b5/0x770 devlink_pernet_pre_exit+0x25d/0x3a0 ops_undo_list+0x1b7/0xb90 cleanup_net+0x47f/0x8a0 The buggy address belongs to the object at ff1100001a379800 which belongs to the cache kmalloc-1k of size 1024 The freed 1k object is the bucket table of data->nexthop_ht. Shortly after, the dangling table is dereferenced again and the machine also takes a GPF in __rht_bucket_nested() from the same call site. The root cause is a lifetime mismatch: the debugfs files reference nsim_fib_data (the writer dereferences data->nexthop_ht), but the interface is not bracketed around the lifetime of that data. nsim_fib_destroy() freed both rhashtables and only removed the debugfs directory afterwards, and nsim_fib_create() created the debugfs files before the rhashtables were initialized and, on the error path, freed them before removing the files. debugfs keeps the file itself alive across a ->write() via debugfs_file_get()/debugfs_file_put() (fs/debugfs/file.c), but it does not keep data->nexthop_ht alive, so the in-flight writer dereferenced freed memory. rtnl_lock() in the writer does not help, because the teardown path does not take rtnl around rhashtable_free_and_destroy(). Fix it by bracketing the debugfs interface around the data it exposes, keeping nsim_fib_create() and nsim_fib_destroy() symmetric: - In nsim_fib_destroy(), tear down the debugfs files before the data structures they reference. debugfs_remove_recursive() drops the initial active-user reference and then waits for every in-flight ->write() to drop its reference before returning, and rejects new opens (__debugfs_file_removed(), fs/debugfs/inode.c). Once it returns, no debugfs accessor can reach the FIB data, so the rhashtables and nsim_fib_data can be destroyed safely. This also covers the bool knobs in the same directory, which store pointers into the same nsim_fib_data, and the final kfree(data). - In nsim_fib_create(), create the debugfs files after the rhashtables and notifiers are set up. This closes the same race on the error-unwind path, where a concurrent writer could otherwise observe a half-constructed instance or a table that the unwind has already freed. (With only the destroy-side change, a writer racing the create window instead dereferences an uninitialized data->nexthop_ht.) This is reproducible by racing, in a loop, writes to /sys/kernel/debug/netdevsim/netdevsimN/fib/nexthop_bucket_activity against a teardown of the same netdevsim instance -- a devlink reload ("devlink dev reload netdevsim/netdevsimN"), destroying the network namespace it lives in, or "echo N > /sys/bus/netdevsim/del_device". It was found with syzkaller; a syzkaller reproducer is available. A standalone C reproducer does not trigger it reliably because the race needs the netns-teardown/reload path. Cc: <stable+noautosel@kernel.org> # netdevsim is a test harness, it's never loaded on production systems Signed-off-by: Zijing Yin <yzjaurora@gmail.com> Reviewed-by: Ido Schimmel <idosch@nvidia.com> Link: https://patch.msgid.link/20260529135718.1804031-1-yzjaurora@gmail.com Signed-off-by: Jakub Kicinski <kuba@kernel.org>
1671 lines
40 KiB
1671 lines
40 KiB