diff mbox series

[1/3] nfsd: make sure exp active before svc_export_show

Message ID 20241021142343.3857891-2-yangerkun@huaweicloud.com (mailing list archive)
State New
Headers show
Series bugfix for c_show/e_show | expand

Commit Message

yangerkun Oct. 21, 2024, 2:23 p.m. UTC 
From: Yang Erkun <yangerkun@huawei.com>

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@huawei.com>
---
 fs/nfsd/export.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

Comments

Chuck Lever Oct. 21, 2024, 5:10 p.m. UTC | #1 
On Mon, Oct 21, 2024 at 10:23:41PM +0800, Yang Erkun wrote:
> From: Yang Erkun <yangerkun@huawei.com>
> 
> 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")

This seems better:

Fixes: bf18f163e89c ("NFSD: Using exp_get for export getting")
Cc: stable@vger.kernel.org # 4.20+


> Signed-off-by: Yang Erkun <yangerkun@huawei.com>
> ---
>  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
>
diff mbox series

Patch

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);
 }