5.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Yang Erkun <yangerkun@xxxxxxxxxx> commit 2862eee078a4d2d1f584e7f24fa50dddfa5f3471 upstream. The function `c_show` was called with protection from RCU. This only ensures that `cp` will not be freed. Therefore, the reference count for `cp` can drop to zero, which will trigger a refcount use-after-free warning when `cache_get` is called. To resolve this issue, use `cache_get_rcu` to ensure that `cp` remains active. ------------[ cut here ]------------ refcount_t: addition on 0; use-after-free. WARNING: CPU: 7 PID: 822 at lib/refcount.c:25 refcount_warn_saturate+0xb1/0x120 CPU: 7 UID: 0 PID: 822 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 RIP: 0010:refcount_warn_saturate+0xb1/0x120 Call Trace: <TASK> c_show+0x2fc/0x380 [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 Cc: stable@xxxxxxxxxxxxxxx # v4.20+ Signed-off-by: Yang Erkun <yangerkun@xxxxxxxxxx> Reviewed-by: Jeff Layton <jlayton@xxxxxxxxxx> Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- net/sunrpc/cache.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) --- a/net/sunrpc/cache.c +++ b/net/sunrpc/cache.c @@ -1407,7 +1407,9 @@ static int c_show(struct seq_file *m, vo seq_printf(m, "# expiry=%ld refcnt=%d flags=%lx\n", convert_to_wallclock(cp->expiry_time), kref_read(&cp->ref), cp->flags); - cache_get(cp); + if (!cache_get_rcu(cp)) + return 0; + if (cache_check(cd, cp, NULL)) /* cache_check does a cache_put on failure */ seq_printf(m, "# ");
