Re: [PATCH v2] nfsd: clear acl_access/acl_default after releasing them

[Chuck Lever <chuck.lever@oracle.com>]

On 1/26/25 8:51 AM, Rick Macklem wrote:
> On Sun, Jan 26, 2025 at 1:29 AM Li Lingfeng <lilingfeng3@huawei.com> wrote:
>>
>> If getting acl_default fails, acl_access and acl_default will be released
>> simultaneously. However, acl_access will still retain a pointer pointing
>> to the released posix_acl, which will trigger a WARNING in
>> nfs3svc_release_getacl like this:
>>
>> ------------[ cut here ]------------
>> refcount_t: underflow; use-after-free.
>> WARNING: CPU: 26 PID: 3199 at lib/refcount.c:28
>> refcount_warn_saturate+0xb5/0x170
>> Modules linked in:
>> CPU: 26 UID: 0 PID: 3199 Comm: nfsd Not tainted
>> 6.12.0-rc6-00079-g04ae226af01f-dirty #8
>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
>> 1.16.1-2.fc37 04/01/2014
>> RIP: 0010:refcount_warn_saturate+0xb5/0x170
>> Code: cc cc 0f b6 1d b3 20 a5 03 80 fb 01 0f 87 65 48 d8 00 83 e3 01 75
>> e4 48 c7 c7 c0 3b 9b 85 c6 05 97 20 a5 03 01 e8 fb 3e 30 ff <0f> 0b eb
>> cd 0f b6 1d 8a3
>> RSP: 0018:ffffc90008637cd8 EFLAGS: 00010282
>> RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffff83904fde
>> RDX: dffffc0000000000 RSI: 0000000000000008 RDI: ffff88871ed36380
>> RBP: ffff888158beeb40 R08: 0000000000000001 R09: fffff520010c6f56
>> R10: ffffc90008637ab7 R11: 0000000000000001 R12: 0000000000000001
>> R13: ffff888140e77400 R14: ffff888140e77408 R15: ffffffff858b42c0
>> FS:  0000000000000000(0000) GS:ffff88871ed00000(0000)
>> knlGS:0000000000000000
>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> CR2: 0000562384d32158 CR3: 000000055cc6a000 CR4: 00000000000006f0
>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>> Call Trace:
>>   <TASK>
>>   ? refcount_warn_saturate+0xb5/0x170
>>   ? __warn+0xa5/0x140
>>   ? refcount_warn_saturate+0xb5/0x170
>>   ? report_bug+0x1b1/0x1e0
>>   ? handle_bug+0x53/0xa0
>>   ? exc_invalid_op+0x17/0x40
>>   ? asm_exc_invalid_op+0x1a/0x20
>>   ? tick_nohz_tick_stopped+0x1e/0x40
>>   ? refcount_warn_saturate+0xb5/0x170
>>   ? refcount_warn_saturate+0xb5/0x170
>>   nfs3svc_release_getacl+0xc9/0xe0
>>   svc_process_common+0x5db/0xb60
>>   ? __pfx_svc_process_common+0x10/0x10
>>   ? __rcu_read_unlock+0x69/0xa0
>>   ? __pfx_nfsd_dispatch+0x10/0x10
>>   ? svc_xprt_received+0xa1/0x120
>>   ? xdr_init_decode+0x11d/0x190
>>   svc_process+0x2a7/0x330
>>   svc_handle_xprt+0x69d/0x940
>>   svc_recv+0x180/0x2d0
>>   nfsd+0x168/0x200
>>   ? __pfx_nfsd+0x10/0x10
>>   kthread+0x1a2/0x1e0
>>   ? kthread+0xf4/0x1e0
>>   ? __pfx_kthread+0x10/0x10
>>   ret_from_fork+0x34/0x60
>>   ? __pfx_kthread+0x10/0x10
>>   ret_from_fork_asm+0x1a/0x30
>>   </TASK>
>> Kernel panic - not syncing: kernel: panic_on_warn set ...
>>
>> Clear acl_access/acl_default after posix_acl_release is called to prevent
>> UAF from being triggered.
>>
>> Fixes: a257cdd0e217 ("[PATCH] NFSD: Add server support for NFSv3 ACLs.")
>> Link: https://lore.kernel.org/all/20241107014705.2509463-1-lilingfeng@huaweicloud.com/
>> Signed-off-by: Li Lingfeng <lilingfeng3@huawei.com>
>> ---
>> Changes in v2:
>> - Clear acl_access/acl_default after releasing them, instead of
>>    modifying the logic for setting them.
>> - Clear acl_access/acl_default in nfs2acl.c.
>> ---
>>   fs/nfsd/nfs2acl.c | 2 ++
>>   fs/nfsd/nfs3acl.c | 2 ++
>>   2 files changed, 4 insertions(+)
>>
>> diff --git a/fs/nfsd/nfs2acl.c b/fs/nfsd/nfs2acl.c
>> index 4e3be7201b1c..5fb202acb0fd 100644
>> --- a/fs/nfsd/nfs2acl.c
>> +++ b/fs/nfsd/nfs2acl.c
>> @@ -84,6 +84,8 @@ static __be32 nfsacld_proc_getacl(struct svc_rqst *rqstp)
>>   fail:
>>          posix_acl_release(resp->acl_access);
>>          posix_acl_release(resp->acl_default);
>> +       resp->acl_access = NULL;
>> +       resp->acl_default = NULL;
>>          goto out;
>>   }
>>
>> diff --git a/fs/nfsd/nfs3acl.c b/fs/nfsd/nfs3acl.c
>> index 5e34e98db969..7b5433bd3019 100644
>> --- a/fs/nfsd/nfs3acl.c
>> +++ b/fs/nfsd/nfs3acl.c
>> @@ -76,6 +76,8 @@ static __be32 nfsd3_proc_getacl(struct svc_rqst *rqstp)
>>   fail:
>>          posix_acl_release(resp->acl_access);
>>          posix_acl_release(resp->acl_default);
>> +       resp->acl_access = NULL;
>> +       resp->acl_default = NULL;
>>          goto out;
>>   }
>>
>> --
>> 2.31.1
>>
> This version looks fine to me, rick

Rick, may I add:

Reviewed-by: Rick Macklem <rmacklem@uoguelph.ca>

?

-- 
Chuck Lever