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Wed, 6 May 2026 13:56:18 +0000 (GMT) Message-ID: Date: Wed, 6 May 2026 19:26:16 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 3/9] crash_dump: Disallow writing to dm-crypt configfs during kexec_file_load syscall To: Coiby Xu , kexec@lists.infradead.org Cc: Andrew Morton , Baoquan He , Dave Young , Mike Rapoport , Pasha Tatashin , Pratyush Yadav , Coiby Xu , open list References: <20260501234342.2518281-1-coiby.xu@gmail.com> <20260501234342.2518281-4-coiby.xu@gmail.com> Content-Language: en-US From: Sourabh Jain In-Reply-To: <20260501234342.2518281-4-coiby.xu@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNTA2MDEzNCBTYWx0ZWRfX+OIqKkBCeiFx bcZ+n+v/FfXDCXC8oJi80fhWrzVjspMHE+SG5ZNvSsGCwpeNcl+Io+QnRYFUHfy5lZhomNoNcFV 1+j3R8z/j5MC2pK12Is87+CU3XGuJsRZKfErvj7OdToIZtCIAykr64nwIMlfj4dTKRs9iNdi5WX FVG5rk3cKmQ9KwmP4jHAfDylL46VRkHSn/ceOgTyUa4NatxHDIAj43+ERIGqeP0SluhQt/5CxXU wF/JYzVAneDH/cWH2+uv6PUG9kD3AVyLQpOrP5DFpDQn2oBfD5B2KH3VLasQGPAZqy+5p1P6Gc7 QxTt4TwJhnBZTKLk4sLavcwUgDz3AW5DdUMWJj4rZhGb+DsY0NUAdQmtWXbl1F6so/w0PT3zz9p Dd6csN7VQc6ePGUarc3J8NPn3xKsvgboL42gsgKhNFl8DpAc76CaysijI4e+133cBNTUb2Ev5yw PvgYZQNHqMqEDh1KarQ== X-Authority-Analysis: v=2.4 cv=J4GaKgnS c=1 sm=1 tr=0 ts=69fb4889 cx=c_pps a=bLidbwmWQ0KltjZqbj+ezA==:117 a=bLidbwmWQ0KltjZqbj+ezA==:17 a=IkcTkHD0fZMA:10 a=NGcC8JguVDcA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=RzCfie-kr_QcCd8fBx8p:22 a=pGLkceISAAAA:8 a=yykyRpDHwrTCM8KGDVYA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 X-Proofpoint-GUID: Sq2gUFsxyOg-spKC2V7oQqoOsWaaahR3 X-Proofpoint-ORIG-GUID: ZzVuH9N9anvlaACgUbC4Kjzf_M6QvfKX X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-05-05_03,2026-05-06_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 clxscore=1015 malwarescore=0 bulkscore=0 suspectscore=0 priorityscore=1501 spamscore=0 phishscore=0 adultscore=0 lowpriorityscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2604200000 definitions=main-2605060134 On 02/05/26 05:13, Coiby Xu wrote: > If writing to the configfs group happens concurrently during > kexec_file_load syscall, it may lead to the following issues, > - buffer overflow if dm-crypt keys are added after allocation > - stale total_keys if dm-crypt keys are removed during iteration > - keys_header will not be freed if config/crash_dm_crypt_key/reuse is > set true > > So hold config_keys_subsys.su_mutex for the entire sequence during the > kexec_file_load syscall to ensure a consistent snapshot. Yes, this will solve many synchronization problems when a  user tries to perform any operation under our configfs_subsystem while the kernel is executing the kexec_file_load system call. Now, regarding the third point about freeing key_header: this will work only if configfs takes the su_mutex lock before invoking the store callback. I am not sure whether it actually does. However, based on my previous comment on (2/9), if we keep config_keys_reuse_store() under the kexec lock, this will be taken care of. This is because the entire kexec_file_load system call already runs under the kexec lock. > > Fixes: 479e58549b0f ("crash_dump: store dm crypt keys in kdump reserved memory") > Signed-off-by: Coiby Xu > --- > kernel/crash_dump_dm_crypt.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/kernel/crash_dump_dm_crypt.c b/kernel/crash_dump_dm_crypt.c > index 4d8a3331bbe7..6377ee86ec50 100644 > --- a/kernel/crash_dump_dm_crypt.c > +++ b/kernel/crash_dump_dm_crypt.c > @@ -429,6 +429,7 @@ int crash_load_dm_crypt_keys(struct kimage *image) > }; > int r = 0; > > + mutex_lock(&config_keys_subsys.su_mutex); > > if (key_count <= 0) { > kexec_dprintk("No dm-crypt keys\n"); > @@ -479,6 +480,9 @@ void kexec_file_post_load_cleanup_dm_crypt(struct kimage *image) > kfree_sensitive(keys_header); > keys_header = NULL; > } > + > + if (mutex_is_locked(&config_keys_subsys.su_mutex)) > + mutex_unlock(&config_keys_subsys.su_mutex); How about release the lock in crash_load_dm_crypt_keys() itself? Given that config_keys_reuse_store() is placed under kexec lock? - Sourabh Jain > } > > static int __init configfs_dmcrypt_keys_init(void)