On Mon, Oct 21, 2024 at 10:23:43PM +0800, Yang Erkun wrote:
> From: Yang Erkun <yangerkun@xxxxxxxxxx>
>
> The last reference for `cache_head` can be reduced to zero in `c_show`
> and `e_show`(using `rcu_read_lock` and `rcu_read_unlock`). Consequently,
> `svc_export_put` and `expkey_put` will be invoked, leading to two
> issues:
>
> 1. The `svc_export_put` will directly free ex_uuid. However,
> `e_show`/`c_show` will access `ex_uuid` after `cache_put`, which can
> trigger a use-after-free issue, shown below.
>
> ==================================================================
> BUG: KASAN: slab-use-after-free in svc_export_show+0x362/0x430 [nfsd]
> Read of size 1 at addr ff11000010fdc120 by task cat/870
>
> CPU: 1 UID: 0 PID: 870 Comm: cat Not tainted 6.12.0-rc3+ #1
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
> 1.16.1-2.fc37 04/01/2014
> Call Trace:
> <TASK>
> dump_stack_lvl+0x53/0x70
> print_address_description.constprop.0+0x2c/0x3a0
> print_report+0xb9/0x280
> kasan_report+0xae/0xe0
> svc_export_show+0x362/0x430 [nfsd]
> c_show+0x161/0x390 [sunrpc]
> seq_read_iter+0x589/0x770
> seq_read+0x1e5/0x270
> proc_reg_read+0xe1/0x140
> vfs_read+0x125/0x530
> ksys_read+0xc1/0x160
> do_syscall_64+0x5f/0x170
> entry_SYSCALL_64_after_hwframe+0x76/0x7e
>
> Allocated by task 830:
> kasan_save_stack+0x20/0x40
> kasan_save_track+0x14/0x30
> __kasan_kmalloc+0x8f/0xa0
> __kmalloc_node_track_caller_noprof+0x1bc/0x400
> kmemdup_noprof+0x22/0x50
> svc_export_parse+0x8a9/0xb80 [nfsd]
> cache_do_downcall+0x71/0xa0 [sunrpc]
> cache_write_procfs+0x8e/0xd0 [sunrpc]
> proc_reg_write+0xe1/0x140
> vfs_write+0x1a5/0x6d0
> ksys_write+0xc1/0x160
> do_syscall_64+0x5f/0x170
> entry_SYSCALL_64_after_hwframe+0x76/0x7e
>
> Freed by task 868:
> kasan_save_stack+0x20/0x40
> kasan_save_track+0x14/0x30
> kasan_save_free_info+0x3b/0x60
> __kasan_slab_free+0x37/0x50
> kfree+0xf3/0x3e0
> svc_export_put+0x87/0xb0 [nfsd]
> cache_purge+0x17f/0x1f0 [sunrpc]
> nfsd_destroy_serv+0x226/0x2d0 [nfsd]
> nfsd_svc+0x125/0x1e0 [nfsd]
> write_threads+0x16a/0x2a0 [nfsd]
> nfsctl_transaction_write+0x74/0xa0 [nfsd]
> vfs_write+0x1a5/0x6d0
> ksys_write+0xc1/0x160
> do_syscall_64+0x5f/0x170
> entry_SYSCALL_64_after_hwframe+0x76/0x7e
>
> 2. We cannot sleep while using `rcu_read_lock`/`rcu_read_unlock`.
> However, `svc_export_put`/`expkey_put` will call path_put, which
> subsequently triggers a sleeping operation due to the following
> `dput`.
>
> =============================
> WARNING: suspicious RCU usage
> 5.10.0-dirty #141 Not tainted
> -----------------------------
> ...
> Call Trace:
> dump_stack+0x9a/0xd0
> ___might_sleep+0x231/0x240
> dput+0x39/0x600
> path_put+0x1b/0x30
> svc_export_put+0x17/0x80
> e_show+0x1c9/0x200
> seq_read_iter+0x63f/0x7c0
> seq_read+0x226/0x2d0
> vfs_read+0x113/0x2c0
> ksys_read+0xc9/0x170
> do_syscall_64+0x33/0x40
> entry_SYSCALL_64_after_hwframe+0x67/0xd1
>
> Fix these issues by using `rcu_work` to help release
> `svc_expkey`/`svc_export`. This approach allows for an asynchronous
> context to invoke `path_put` and also facilitates the freeing of
> `uuid/exp/key` after an RCU grace period.
>
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
I'd go with:
Fixes: 9ceddd9da134 ("knfsd: Allow lockless lookups of the exports")
I plan to apply these three to nfsd-next (for v6.13).
> Signed-off-by: Yang Erkun <yangerkun@xxxxxxxxxx>
> ---
> fs/nfsd/export.c | 31 +++++++++++++++++++++++++------
> fs/nfsd/export.h | 4 ++--
> 2 files changed, 27 insertions(+), 8 deletions(-)
>
> diff --git a/fs/nfsd/export.c b/fs/nfsd/export.c
> index 49aede376d86..6d0455973d64 100644
> --- a/fs/nfsd/export.c
> +++ b/fs/nfsd/export.c
> @@ -40,15 +40,24 @@
> #define EXPKEY_HASHMAX (1 << EXPKEY_HASHBITS)
> #define EXPKEY_HASHMASK (EXPKEY_HASHMAX -1)
>
> -static void expkey_put(struct kref *ref)
> +static void expkey_put_work(struct work_struct *work)
> {
> - struct svc_expkey *key = container_of(ref, struct svc_expkey, h.ref);
> + struct svc_expkey *key =
> + container_of(to_rcu_work(work), struct svc_expkey, ek_rcu_work);
>
> if (test_bit(CACHE_VALID, &key->h.flags) &&
> !test_bit(CACHE_NEGATIVE, &key->h.flags))
> path_put(&key->ek_path);
> auth_domain_put(key->ek_client);
> - kfree_rcu(key, ek_rcu);
> + kfree(key);
> +}
> +
> +static void expkey_put(struct kref *ref)
> +{
> + struct svc_expkey *key = container_of(ref, struct svc_expkey, h.ref);
> +
> + INIT_RCU_WORK(&key->ek_rcu_work, expkey_put_work);
> + queue_rcu_work(system_wq, &key->ek_rcu_work);
> }
>
> static int expkey_upcall(struct cache_detail *cd, struct cache_head *h)
> @@ -355,16 +364,26 @@ static void export_stats_destroy(struct export_stats *stats)
> EXP_STATS_COUNTERS_NUM);
> }
>
> -static void svc_export_put(struct kref *ref)
> +static void svc_export_put_work(struct work_struct *work)
> {
> - struct svc_export *exp = container_of(ref, struct svc_export, h.ref);
> + struct svc_export *exp =
> + container_of(to_rcu_work(work), struct svc_export, ex_rcu_work);
> +
> path_put(&exp->ex_path);
> auth_domain_put(exp->ex_client);
> nfsd4_fslocs_free(&exp->ex_fslocs);
> export_stats_destroy(exp->ex_stats);
> kfree(exp->ex_stats);
> kfree(exp->ex_uuid);
> - kfree_rcu(exp, ex_rcu);
> + kfree(exp);
> +}
> +
> +static void svc_export_put(struct kref *ref)
> +{
> + struct svc_export *exp = container_of(ref, struct svc_export, h.ref);
> +
> + INIT_RCU_WORK(&exp->ex_rcu_work, svc_export_put_work);
> + queue_rcu_work(system_wq, &exp->ex_rcu_work);
> }
>
> static int svc_export_upcall(struct cache_detail *cd, struct cache_head *h)
> diff --git a/fs/nfsd/export.h b/fs/nfsd/export.h
> index 3794ae253a70..081afb68681e 100644
> --- a/fs/nfsd/export.h
> +++ b/fs/nfsd/export.h
> @@ -75,7 +75,7 @@ struct svc_export {
> u32 ex_layout_types;
> struct nfsd4_deviceid_map *ex_devid_map;
> struct cache_detail *cd;
> - struct rcu_head ex_rcu;
> + struct rcu_work ex_rcu_work;
> unsigned long ex_xprtsec_modes;
> struct export_stats *ex_stats;
> };
> @@ -92,7 +92,7 @@ struct svc_expkey {
> u32 ek_fsid[6];
>
> struct path ek_path;
> - struct rcu_head ek_rcu;
> + struct rcu_work ek_rcu_work;
> };
>
> #define EX_ISSYNC(exp) (!((exp)->ex_flags & NFSEXP_ASYNC))
> --
> 2.39.2
>
--
Chuck Lever
