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From: Benjamin Coddington <bcodding@redhat.com>
To: Jorge Mora <jmora1300@gmail.com>
Cc: linux-nfs@vger.kernel.org, trond.myklebust@hammerspace.com,
 anna@kernel.org
Subject: Re: [PATCH] NFSv4.2: fix nfs4_listxattr kernel BUG at
 mm/usercopy.c:102
Date: Fri, 26 Jan 2024 09:49:43 -0500
Message-ID: <8D1EF949-6A21-4839-B044-6AD4ABD49614@redhat.com>
In-Reply-To: <20240125145613.12995-1-mora@netapp.com>
References: <20240125145613.12995-1-mora@netapp.com>
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On 25 Jan 2024, at 9:56, Jorge Mora wrote:

> A call to listxattr() with a buffer size = 0 returns the actual
> size of the buffer needed for a subsequent call. When size > 0,
> nfs4_listxattr() does not return an error because either
> generic_listxattr() or nfs4_listxattr_nfs4_label() consumes
> exactly all the bytes then size is 0 when calling
> nfs4_listxattr_nfs4_user() which then triggers the following
> kernel BUG:
>
>   [   99.403778] kernel BUG at mm/usercopy.c:102!
>   [   99.404063] Internal error: Oops - BUG: 00000000f2000800 [#1] SMP
>   [   99.408463] CPU: 0 PID: 3310 Comm: python3 Not tainted 6.6.0-61.fc40.aarch64 #1
>   [   99.415827] Call trace:
>   [   99.415985]  usercopy_abort+0x70/0xa0
>   [   99.416227]  __check_heap_object+0x134/0x158
>   [   99.416505]  check_heap_object+0x150/0x188
>   [   99.416696]  __check_object_size.part.0+0x78/0x168
>   [   99.416886]  __check_object_size+0x28/0x40
>   [   99.417078]  listxattr+0x8c/0x120
>   [   99.417252]  path_listxattr+0x78/0xe0
>   [   99.417476]  __arm64_sys_listxattr+0x28/0x40
>   [   99.417723]  invoke_syscall+0x78/0x100
>   [   99.417929]  el0_svc_common.constprop.0+0x48/0xf0
>   [   99.418186]  do_el0_svc+0x24/0x38
>   [   99.418376]  el0_svc+0x3c/0x110
>   [   99.418554]  el0t_64_sync_handler+0x120/0x130
>   [   99.418788]  el0t_64_sync+0x194/0x198
>   [   99.418994] Code: aa0003e3 d000a3e0 91310000 97f49bdb (d4210000)
>
> Issue is reproduced when generic_listxattr() returns 'system.nfs4_acl',
> thus calling lisxattr() with size = 16 will trigger the bug.
>
> Add check on nfs4_listxattr() to return ERANGE error when it is
> called with size > 0 and the return value is greater than size.
>
> Fixes: 012a211abd5d ("NFSv4.2: hook in the user extended attribute handlers")
> Signed-off-by: Jorge Mora <mora@netapp.com>

Reviewed-by: Benjamin Coddington <bcodding@redhat.com>

Ben