linux-kernel - Re: [PATCH] nfs: handle failure of nfs_get_lock

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Message-ID: <678aae33-3af0-4229-a2ce-d9cef1572f96@huawei.com>
Date: Thu, 17 Apr 2025 20:24:18 +0800
From: Li Lingfeng <lilingfeng3@...wei.com>
To: Jeff Layton <jlayton@...nel.org>, <trondmy@...nel.org>, <anna@...nel.org>,
	<bcodding@...hat.com>
CC: <linux-nfs@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<yukuai1@...weicloud.com>, <houtao1@...wei.com>, <yi.zhang@...wei.com>,
	<yangerkun@...wei.com>, <lilingfeng@...weicloud.com>
Subject: Re: [PATCH] nfs: handle failure of nfs_get_lock_context in unlock
 path


在 2025/4/17 18:29, Jeff Layton 写道:
> On Thu, 2025-04-17 at 15:25 +0800, Li Lingfeng wrote:
>> When memory is insufficient, the allocation of nfs_lock_context in
>> nfs_get_lock_context() fails and returns -ENOMEM. If we mistakenly treat
>> an nfs4_unlockdata structure (whose l_ctx member has been set to -ENOMEM)
>> as valid and proceed to execute rpc_run_task(), this will trigger a NULL
>> pointer dereference in nfs4_locku_prepare. For example:
>>
>> BUG: kernel NULL pointer dereference, address: 000000000000000c
>> PGD 0 P4D 0
>> Oops: Oops: 0000 [#1] SMP PTI
>> CPU: 15 UID: 0 PID: 12 Comm: kworker/u64:0 Not tainted 6.15.0-rc2-dirty #60
>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-2.fc40
>> Workqueue: rpciod rpc_async_schedule
>> RIP: 0010:nfs4_locku_prepare+0x35/0xc2
>> Code: 89 f2 48 89 fd 48 c7 c7 68 69 ef b5 53 48 8b 8e 90 00 00 00 48 89 f3
>> RSP: 0018:ffffbbafc006bdb8 EFLAGS: 00010246
>> RAX: 000000000000004b RBX: ffff9b964fc1fa00 RCX: 0000000000000000
>> RDX: 0000000000000000 RSI: fffffffffffffff4 RDI: ffff9ba53fddbf40
>> RBP: ffff9ba539934000 R08: 0000000000000000 R09: ffffbbafc006bc38
>> R10: ffffffffb6b689c8 R11: 0000000000000003 R12: ffff9ba539934030
>> R13: 0000000000000001 R14: 0000000004248060 R15: ffffffffb56d1c30
>> FS: 0000000000000000(0000) GS:ffff9ba5881f0000(0000) knlGS:00000000
>> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> CR2: 000000000000000c CR3: 000000093f244000 CR4: 00000000000006f0
>> Call Trace:
>>   <TASK>
>>   __rpc_execute+0xbc/0x480
>>   rpc_async_schedule+0x2f/0x40
>>   process_one_work+0x232/0x5d0
>>   worker_thread+0x1da/0x3d0
>>   ? __pfx_worker_thread+0x10/0x10
>>   kthread+0x10d/0x240
>>   ? __pfx_kthread+0x10/0x10
>>   ret_from_fork+0x34/0x50
>>   ? __pfx_kthread+0x10/0x10
>>   ret_from_fork_asm+0x1a/0x30
>>   </TASK>
>> Modules linked in:
>> CR2: 000000000000000c
>> ---[ end trace 0000000000000000 ]---
>>
>> Free the allocated nfs4_unlockdata when nfs_get_lock_context() fails and
>> return NULL to terminate subsequent rpc_run_task, preventing NULL pointer
>> dereference.
>>
>> Fixes: f30cb757f680 ("NFS: Always wait for I/O completion before unlock")
>> Signed-off-by: Li Lingfeng <lilingfeng3@...wei.com>
>> ---
>>   fs/nfs/nfs4proc.c | 9 ++++++++-
>>   1 file changed, 8 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
>> index 970f28dbf253..9f5689c43a50 100644
>> --- a/fs/nfs/nfs4proc.c
>> +++ b/fs/nfs/nfs4proc.c
>> @@ -7074,10 +7074,18 @@ static struct nfs4_unlockdata *nfs4_alloc_unlockdata(struct file_lock *fl,
>>   	struct nfs4_unlockdata *p;
>>   	struct nfs4_state *state = lsp->ls_state;
>>   	struct inode *inode = state->inode;
>> +	struct nfs_lock_context *l_ctx;
>>   
>>   	p = kzalloc(sizeof(*p), GFP_KERNEL);
>>   	if (p == NULL)
>>   		return NULL;
>> +	l_ctx = nfs_get_lock_context(ctx);
>> +	if (!IS_ERR(l_ctx)) {
>> +		p->l_ctx = l_ctx;
>> +	} else {
>> +		kfree(p);
>> +		return NULL;
>> +	}
>>   	p->arg.fh = NFS_FH(inode);
>>   	p->arg.fl = &p->fl;
>>   	p->arg.seqid = seqid;
>> @@ -7085,7 +7093,6 @@ static struct nfs4_unlockdata *nfs4_alloc_unlockdata(struct file_lock *fl,
>>   	p->lsp = lsp;
>>   	/* Ensure we don't close file until we're done freeing locks! */
>>   	p->ctx = get_nfs_open_context(ctx);
> Not exactly the same problem, but get_nfs_open_context() can fail too.
> Does it need error handling for that as well?

Hi,

IIUC, nfs_open_context is allocated during file open and attached to
filp->private_data. Upon successful file opening, the context remains valid.
Post-lock acquisition, nfs_open_context can be retrieved via
file_lock->file->nfs_open_context chain. Thus get_nfs_open_context() here
should have non-failure guarantee in standard code paths.

Best regards,
Lingfeng

>
>> -	p->l_ctx = nfs_get_lock_context(ctx);
>>   	locks_init_lock(&p->fl);
>>   	locks_copy_lock(&p->fl, fl);
>>   	p->server = NFS_SERVER(inode);
> Good catch:
>
> Reviewed-by: Jeff Layton <jlayton@...nel.org>
>