From: Yang Erkun <yangerkun@xxxxxxxxxx>
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
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Yang Erkun <yangerkun@xxxxxxxxxx>
---
net/sunrpc/cache.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c
index 1bd3e531b0e0..059f6ef1ad18 100644
--- a/net/sunrpc/cache.c
+++ b/net/sunrpc/cache.c
@@ -1427,7 +1427,9 @@ static int c_show(struct seq_file *m, void *p)
seq_printf(m, "# expiry=%lld 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_puts(m, "# ");
--
2.39.2
