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From: Roman Gushchin To: Parav Pandit Cc: Jason Gunthorpe , Leon Romanovsky , Maher Sanalla , "linux-rdma@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] RDMA/core: fix a NULL-pointer dereference in hw_stat_device_show() Message-ID: References: <20250221020555.4090014-1-roman.gushchin@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT On Fri, Feb 21, 2025 at 03:14:16AM +0000, Parav Pandit wrote: > > > From: Roman Gushchin > > Sent: Friday, February 21, 2025 7:36 AM > > > > Commit 54747231150f ("RDMA: Introduce and use rdma_device_to_ibdev()") > > introduced rdma_device_to_ibdev() helper which has to be used to obtain an > > ib_device pointer from a device pointer. > > > > > hw_stat_device_show() and hw_stat_device_store() were missed. > > > > It causes a NULL pointer dereference panic on an attempt to read hw counters > > from a namespace, when the device structure is not embedded into the > > ib_device structure. > Do you mean net namespace other than default init_net? > Assuming the answer is yes, some question below. > > > In this case casting the device pointer into the ib_device > > pointer using container_of() is wrong. > > Instead, rdma_device_to_ibdev() should be used, which uses the back- > > reference (container_of(device, struct ib_core_device, dev))->owner. > > > > [42021.807566] BUG: kernel NULL pointer dereference, address: > > 0000000000000028 [42021.814463] #PF: supervisor read access in kernel > > mode [42021.819549] #PF: error_code(0x0000) - not-present page > > [42021.824636] PGD 0 P4D 0 [42021.827145] Oops: 0000 [#1] SMP PTI > > [42021.830598] CPU: 82 PID: 2843922 Comm: switchto-defaul Kdump: loaded > > Tainted: G S W I XXX > > [42021.841697] Hardware name: XXX > > [42021.849619] RIP: 0010:hw_stat_device_show+0x1e/0x40 [ib_core] > > [42021.855362] Code: 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 0f 1f > > 44 00 00 49 89 d0 4c 8b 5e 20 48 8b 8f b8 04 00 00 48 81 c7 f0 fa ff ff <48> 8b > > 41 28 48 29 ce 48 83 c6 d0 48 c1 ee 04 69 d6 ab aa aa aa 48 [42021.873931] > > RSP: 0018:ffff97fe90f03da0 EFLAGS: 00010287 [42021.879108] RAX: > > ffff9406988a8c60 RBX: ffff940e1072d438 RCX: 0000000000000000 > > [42021.886169] RDX: ffff94085f1aa000 RSI: ffff93c6cbbdbcb0 RDI: > > ffff940c7517aef0 [42021.893230] RBP: ffff97fe90f03e70 R08: > > ffff94085f1aa000 R09: 0000000000000000 [42021.900294] R10: > > ffff94085f1aa000 R11: ffffffffc0775680 R12: ffffffff87ca2530 [42021.907355] > > R13: ffff940651602840 R14: ffff93c6cbbdbcb0 R15: ffff94085f1aa000 > > [42021.914418] FS: 00007fda1a3b9700(0000) GS:ffff94453fb80000(0000) > > knlGS:0000000000000000 [42021.922423] CS: 0010 DS: 0000 ES: 0000 CR0: > > 0000000080050033 [42021.928130] CR2: 0000000000000028 CR3: > > 00000042dcfb8003 CR4: 00000000003726f0 [42021.935194] DR0: > > 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > > [42021.942257] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: > > 0000000000000400 [42021.949324] Call Trace: > > [42021.951756] > > [42021.953842] [] ? show_regs+0x64/0x70 [42021.959030] > > [] ? __die+0x78/0xc0 [42021.963874] [] ? > > page_fault_oops+0x2b5/0x3b0 [42021.969749] [] ? > > exc_page_fault+0x1a2/0x3c0 [42021.975549] [] ? > > asm_exc_page_fault+0x26/0x30 [42021.981517] [] ? > > __pfx_show_hw_stats+0x10/0x10 [ib_core] [42021.988482] > > [] ? hw_stat_device_show+0x1e/0x40 [ib_core] > > [42021.995438] [] dev_attr_show+0x1e/0x50 > > [42022.000803] [] sysfs_kf_seq_show+0x81/0xe0 > > [42022.006508] [] seq_read_iter+0xf4/0x410 > > [42022.011954] [] vfs_read+0x16e/0x2f0 [42022.017058] > > [] ksys_read+0x6e/0xe0 [42022.022073] [] > > do_syscall_64+0x6a/0xa0 [42022.027441] [] > > entry_SYSCALL_64_after_hwframe+0x78/0xe2 > > > > Fixes: 54747231150f ("RDMA: Introduce and use rdma_device_to_ibdev()") > Commit eb15c78b05bd9 eliminated hw_counters sysfs directory into the net namespace. > I don't see it created in any other net ns other than init_net with kernel 6.12+. > > I am puzzled. Can you please explain/share the reproduction steps for generating above call trace? Hi Parav! This bug was spotted in the production on a small number of machines. They were running a 6.6-based kernel (with no changes around this code). I don't have a reproducer (and there is no simple way for me to reproduce the problem), but I've several core dumps and from inspecting them it was clear that a ib_device pointer obtained in hw_stat_device_show() was wrong. At the same time the ib_pointer obtained in the way rdma_device_to_ibdev() works was correct. Thanks!