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Date: Mon, 26 Feb 2024 16:43:52 +0100
From: Jiri Pirko <jiri@resnulli.us>
To: Alexander Lobakin <aleksander.lobakin@intel.com>
Cc: "David S. Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	Michael Chan <michael.chan@broadcom.com>,
	Somnath Kotur <somnath.kotur@broadcom.com>,
	Pavan Chebbi <pavan.chebbi@broadcom.com>,
	Kalesh AP <kalesh-anakkur.purayil@broadcom.com>,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH net-next] bnxt_en: fix accessing vnic_info before
 allocating it
Message-ID: <ZdyxuDFY9_LpXr89@nanopsycho>
References: <20240226144911.1297336-1-aleksander.lobakin@intel.com>
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In-Reply-To: <20240226144911.1297336-1-aleksander.lobakin@intel.com>

Mon, Feb 26, 2024 at 03:49:11PM CET, aleksander.lobakin@intel.com wrote:
>bnxt_alloc_mem() dereferences ::vnic_info in the variable declaration
>block, but allocates it much later. As a result, the following crash
>happens on my setup:
>
> BUG: kernel NULL pointer dereference, address: 0000000000000090
> fbcon: Taking over console
> #PF: supervisor write access in kernel mode
> #PF: error_code (0x0002) - not-present page
> PGD 12f382067 P4D 0
> Oops: 8002 [#1] PREEMPT SMP NOPTI
> CPU: 47 PID: 2516 Comm: NetworkManager Not tainted 6.8.0-rc5-libeth+ #49
> Hardware name: Intel Corporation M50CYP2SBSTD/M58CYP2SBSTD, BIOS SE5C620.86B.01.01.0088.2305172341 05/17/2023
> RIP: 0010:bnxt_alloc_mem+0x1609/0x1910 [bnxt_en]
> Code: 81 c8 48 83 c8 08 31 c9 e9 d7 fe ff ff c7 44 24 Oc 00 00 00 00 49 89 d5 e9 2d fe ff ff 41 89 c6 e9 88 00 00 00 48 8b 44 24 50 <80> 88 90 00 00 00 Od 8b 43 74 a8 02 75 1e f6 83 14 02 00 00 80 74
> RSP: 0018:ff3f25580f3432c8 EFLAGS: 00010246
> RAX: 0000000000000000 RBX: ff15a5cfc45249e0 RCX: 0000002079777000
> RDX: ff15a5dfb9767000 RSI: 0000000000000000 RDI: 0000000000000000
> RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
> R10: ff15a5dfb9777000 R11: ffffff8000000000 R12: 0000000000000000
> R13: 0000000000000000 R14: 0000000000000020 R15: ff15a5cfce34f540
> FS:  000007fb9a160500(0000) GS:ff15a5dfbefc0000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CRO: 0000000080050033
> CR2: 0000000000000090 CR3: 0000000109efc00Z CR4: 0000000000771ef0
> DR0: 0000000000000000 DR1: 0000000000000000 DRZ: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> PKRU: 55555554
>
> Call Trace:
> <TASK>
> ? __die_body+0x68/0xb0
> ? page_fault_oops+0x3a6/0x400
> ? exc_page_fault+0x7a/0x1b0
> ? asm_exc_page_fault+0x26/8x30
> ? bnxt_alloc_mem+0x1609/0x1910 [bnxt_en]
> ? bnxt_alloc_mem+0x1389/8x1918 [bnxt_en]
> _bnxt_open_nic+0x198/0xa50 [bnxt_en]
> ? bnxt_hurm_if_change+0x287/0x3d0 [bnxt_en]
> bnxt_open+0xeb/0x1b0 [bnxt_en]
> _dev_open+0x12e/0x1f0
> _dev_change_flags+0xb0/0x200
> dev_change_flags+0x25/0x60
> do_setlink+0x463/0x1260
> ? sock_def_readable+0x14/0xc0
> ? rtnl_getlink+0x4b9/0x590
> ? _nla_validate_parse+0x91/0xfa0
> rtnl_newlink+0xbac/0xe40
> <...>
>
>Don't create a variable and dereference the first array member directly
>since it's used only once in the code.
>
>Fixes: ef4ee64e9990 ("bnxt_en: Define BNXT_VNIC_DEFAULT for the default vnic index")

Nice example how things may go off when patch is doing multiple things
at once :)


>Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>

Reviewed-by: Jiri Pirko <jiri@nvidia.com>