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Wed, 5 Aug 2026 10:30:52 +0000 (GMT) Message-ID: <3010bbe1-844f-4513-9941-f4e92e581769@linux.ibm.com> Date: Wed, 5 Aug 2026 16:00:51 +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 v3 03/10] 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 , Pratyush Yadav , Mike Rapoport , Pasha Tatashin , Coiby Xu , open list References: <20260729033654.311541-1-coiby.xu@gmail.com> <20260729033654.311541-4-coiby.xu@gmail.com> Content-Language: en-US From: Sourabh Jain In-Reply-To: <20260729033654.311541-4-coiby.xu@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-Spam-Info: AW1haW4tMjYwODA1MDA4MSBTYWx0ZWRfX7gzgYwdN90ki kLqlAfUI8aer0EJ/eHHL+PKTW8Yl4Z67YF9RjhQVsy0/P0QfL/kYk9qafETNuETh7F2m3DduUeM ImeOSITGkdSsJhcx+oQpL2oHnprpOnE= X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwODA1MDA4MSBTYWx0ZWRfX0zWEHJKQId/R u17Y0qdhwVdpmtHs+PVQAot52URf5QOr8nIHyfGw2Q4XqVZeIOIIpd29qR0cUDexB5yldJdvD6S bMmH7meEi8pytTX9+Wj3ii0RPdGskWKi5vxO7YALWxr9DgUc7zij0AoqQHcCqbGL3pEkFFK6MZn EzGidPqo76uC3jjmOUPYhLs9qBNoc4Y1Gtuxm8m75CB1pseFw2Ijyjg0y1ihgD47/SeiDta7vsv 5RALeL2JHGtbPmpjmK6YLdV/e5hVVesxQr1C2xYCB8+RFZHCFELwUYDunswjzGgWoqSnF4l2UZv jiNbLn2HGrFQB2SJcoL8TQkdlQXF+fK/+QWAzWXE/41xsy+RP8OeqYhfw8nMtAqPcpxUVWsYHLJ JxftE52vuc6M+E5mS0VjOd52+DpWeJZYr1P6s3xpT7obJJDpCNmbRvsSUUF9mx6oVAi8un0Nn2x NoOk3Fe0xYZxXG+MZww== X-Authority-Analysis: v=2.4 cv=SI1ykuvH c=1 sm=1 tr=0 ts=6a7310e4 cx=c_pps a=GFwsV6G8L6GxiO2Y/PsHdQ==:117 a=GFwsV6G8L6GxiO2Y/PsHdQ==:17 a=IkcTkHD0fZMA:10 a=Sv0fKeRqtYgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=U7nrCbtTmkRpXpFmAIza:22 a=VnNF1IyMAAAA:8 a=pGLkceISAAAA:8 a=qB5L7vjBzVN11irf6e0A:9 a=QEXdDO2ut3YA:10 X-Proofpoint-ORIG-GUID: bHvENgRU6N_wDshmNENwktW58PeysO_u X-Proofpoint-GUID: -q2g72MqoFLV_YVMmIpVM7QksTSMsIIA X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-08-05_03,2026-08-04_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1011 bulkscore=0 suspectscore=0 impostorscore=0 spamscore=0 phishscore=0 priorityscore=1501 lowpriorityscore=0 adultscore=0 malwarescore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2608050081 On 29/07/26 09:06, 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. > > Fixes: 479e58549b0f ("crash_dump: store dm crypt keys in kdump reserved memory") > Suggested-by: Sourabh Jain > Signed-off-by: Coiby Xu > --- > kernel/crash_dump_dm_crypt.c | 23 +++++++++++++++++++++-- > 1 file changed, 21 insertions(+), 2 deletions(-) > > diff --git a/kernel/crash_dump_dm_crypt.c b/kernel/crash_dump_dm_crypt.c > index 4335b6cb1fc4..d2e66c6fe6f3 100644 > --- a/kernel/crash_dump_dm_crypt.c > +++ b/kernel/crash_dump_dm_crypt.c > @@ -293,6 +293,7 @@ static ssize_t config_keys_reuse_show(struct config_item *item, char *page) > static ssize_t config_keys_reuse_store(struct config_item *item, > const char *page, size_t count) > { > + struct mutex *lock; > bool val; > int r; > > @@ -302,8 +303,12 @@ static ssize_t config_keys_reuse_store(struct config_item *item, > return -EINVAL; > } > > + lock = &to_config_group(item)->cg_subsys->su_mutex; > + mutex_lock(lock); Is this lock only protecting against races between key reuse and kexec_file_load(), or does it also handle the case where a new key is added during key reuse or kexec_file_load() is running? If it is only intended to protect key reuse versus kexec_file_load(), why can't we use the kexec lock instead? The reason I'm asking is that, in upcoming patches, the key reuse path accesses kexec_crash_image properties and the crash reserved region directly. Doing so without taking the kexec lock (using kexec_trylock()) could lead to race conditions. - Sourabh Jain > + > + r = -EINVAL; > if (kstrtobool(page, &val) || !val) > - return -EINVAL; > + goto unlock; The jump above skips setting count, causing the function to return count instead of -EINVAL. Is this really intended? > > if (is_dm_key_reused) { > pr_info("Already got dm-crypt keys, please continue with kexec_file_load syscall\n"); > @@ -311,11 +316,15 @@ static ssize_t config_keys_reuse_store(struct config_item *item, > r = get_keys_from_kdump_reserved_memory(); > if (r) { > pr_warn("Failed to get dm-crypt keys from reserved memory\n"); > - return r; > + goto unlock; > } > is_dm_key_reused = true; > } > > + r = count; > + > +unlock: > + mutex_unlock(lock); > return count; > } > > @@ -421,6 +430,8 @@ static int build_keys_header(void) > return 0; > } > > +static bool mutex_acquired; > + > int crash_load_dm_crypt_keys(struct kimage *image) > { > struct kexec_buf kbuf = { > @@ -432,6 +443,9 @@ int crash_load_dm_crypt_keys(struct kimage *image) > }; > int r = 0; > > + mutex_lock(&config_keys_subsys.su_mutex); > + mutex_acquired = true; > + > if (key_count <= 0) { > kexec_dprintk("No dm-crypt keys\n"); > return 0; > @@ -481,6 +495,11 @@ void kexec_file_post_load_cleanup_dm_crypt(struct kimage *image) > kfree_sensitive(keys_header); > keys_header = NULL; > } > + > + if (mutex_acquired) { > + mutex_unlock(&config_keys_subsys.su_mutex); > + mutex_acquired = false; > + } > } > > static int __init configfs_dmcrypt_keys_init(void)