From: Yang Erkun <yangerkun@xxxxxxxxxx>
The function `e_show` was called with protection from RCU. This only
ensures that `exp` will not be freed. Therefore, the reference count for
`exp` can drop to zero, which will trigger a refcount use-after-free
warning when `exp_get` is called. To resolve this issue, use
`cache_get_rcu` to ensure that `exp` remains active.
------------[ cut here ]------------
refcount_t: addition on 0; use-after-free.
WARNING: CPU: 3 PID: 819 at lib/refcount.c:25
refcount_warn_saturate+0xb1/0x120
CPU: 3 UID: 0 PID: 819 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>
e_show+0x20b/0x230 [nfsd]
seq_read_iter+0x589/0x770
seq_read+0x1e5/0x270
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>
---
fs/nfsd/export.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/fs/nfsd/export.c b/fs/nfsd/export.c
index c82d8e3e0d4f..49aede376d86 100644
--- a/fs/nfsd/export.c
+++ b/fs/nfsd/export.c
@@ -1406,9 +1406,12 @@ static int e_show(struct seq_file *m, void *p)
return 0;
}
- exp_get(exp);
+ if (!cache_get_rcu(&exp->h))
+ return 0;
+
if (cache_check(cd, &exp->h, NULL))
return 0;
+
exp_put(exp);
return svc_export_show(m, cd, cp);
}
--
2.39.2
