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Sat, 29 Aug 2026 07:02:48 +0000 (GMT) Received: from [9.67.168.106] (unknown [9.67.168.106]) by smtpav01.fra02v.mail.ibm.com (Postfix) with ESMTP; Sat, 29 Aug 2026 07:02:48 +0000 (GMT) Message-ID: <86f3b10d-6fc2-4dbc-a20b-5d2365601be2@linux.ibm.com> Date: Sat, 29 Aug 2026 12:32:46 +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 v4 2/9] 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 , Pratyush Yadav , Mike Rapoport , Pasha Tatashin , open list References: <20260828084900.1496839-1-coiby.xu@gmail.com> <20260828084900.1496839-3-coiby.xu@gmail.com> Content-Language: en-US From: Sourabh Jain In-Reply-To: <20260828084900.1496839-3-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-Authority-Analysis: v=2.4 cv=bc1bluPB c=1 sm=1 tr=0 ts=6a92841f cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=IkcTkHD0fZMA:10 a=Sv0fKeRqtYgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=RzCfie-kr_QcCd8fBx8p:22 a=VnNF1IyMAAAA:8 a=pGLkceISAAAA:8 a=qB5L7vjBzVN11irf6e0A:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 X-Proofpoint-Spam-Info: AW1haW4tMjYwODI5MDA1OSBTYWx0ZWRfXwF/upvELz7dE A8dF5CBEGApjFdJDyFmfEx1TQFECq+NMACuDUqcNX4w4A6O7+LduNGHLiN3hw+i9s7o9SBlDNnA czipNkNeWJZGfM4TVzysZhYh6Tsjzzs= X-Proofpoint-ORIG-GUID: ZvVGOsM6rQs9pyie3E9vGxNwjDMWbLrX X-Proofpoint-GUID: HEeFwjPPEteVzn4Clz4tAvemJvGVmajp X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwODI5MDA1OSBTYWx0ZWRfX0skYbYZFDSlU NrZeiRXcLEf4ZpqgPAabd3pab3rd4l8oAX3S0YWYAmvEUjqFiNmT/9q5vCQ3G+W2cNlCbvc/Wxa 7gEvcFdftJBPPhLyM7Ls6jdbDh4+8+xHihAJv9JAJDedX76bwTdeKPKzoi68vnofyhIkQ0dPFsP ASFomG94tBKsjbpSCaJqjOokAI7LcKQc2msFsgjpXNuWIseim2g/94SoKcUn9sOn47kHg5dHNLw my4/4UHQa/bEE89W651H0VFAM5fM3wkDYFRlGT9F6JKC8Qcu3PoYXHfcCNUzBZpMm7rIv2umT6i KU10kgJhPs8wOKNT4jfYyNqofnWpB8M22adOqa6yNhTbW0RM+C8Ojh0YKCCrZx8BVf1YQvWlJ6D LYwDD51YKDmyJYUlK9NldzYyBdGt7YuoAnXV2VuZOy5LO5ZSwQEJCg65dFnjaPOyzS3Yiv25Y4p 3ncdjR3Qrje6iCbcKxA== 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=2026-08-29_02,2026-08-27_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 suspectscore=0 adultscore=0 malwarescore=0 spamscore=0 lowpriorityscore=0 phishscore=0 clxscore=1015 priorityscore=1501 impostorscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2608290059 On 28/08/26 14:18, 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. To have serial > access to config/crash_dm_crypt_key/reuse, use the kexec lock as we also > need to access kexec_crash_image serially. > > 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 | 28 ++++++++++++++++++++++++---- > 1 file changed, 24 insertions(+), 4 deletions(-) > > diff --git a/kernel/crash_dump_dm_crypt.c b/kernel/crash_dump_dm_crypt.c > index 4335b6cb1fc4..026c7de4ad85 100644 > --- a/kernel/crash_dump_dm_crypt.c > +++ b/kernel/crash_dump_dm_crypt.c > @@ -7,6 +7,7 @@ > #include > #include > #include > +#include "kexec_internal.h" > > #define KEY_NUM_MAX 128 /* maximum dm crypt keys */ > #define KEY_SIZE_MAX 256 /* maximum dm crypt key size */ > @@ -296,14 +297,20 @@ static ssize_t config_keys_reuse_store(struct config_item *item, > bool val; > int r; > > + if (!kexec_trylock()) { > + r = -EBUSY; > + goto unlock; Are we unlocking a lock that we didn't acquire? How about returning -EBUSY directly instead? > + } > + > + r = -EINVAL; > if (!kexec_crash_image || !kexec_crash_image->dm_crypt_keys_addr) { > kexec_dprintk( > "dm-crypt keys haven't be saved to crash-reserved memory\n"); > - return -EINVAL; > + goto unlock; > } > > if (kstrtobool(page, &val) || !val) > - return -EINVAL; > + goto unlock; > > if (is_dm_key_reused) { > pr_info("Already got dm-crypt keys, please continue with kexec_file_load syscall\n"); > @@ -311,12 +318,15 @@ 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; [...] > } > > - return count; > + r = count; > +unlock: > + kexec_unlock(); > + return r; > } > > CONFIGFS_ATTR(config_keys_, reuse); > @@ -421,6 +431,8 @@ 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 +444,9 @@ 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 +496,11 @@ void kexec_file_post_load_cleanup_dm_crypt(struct kimage *image) I explored the kexec_file_load syscall entry path and noticed that there is a path where the call to kimage_file_post_load_cleanup() can be skipped. For example, if kexec_file_load is called and everything goes well but kexec_post_load() fails, we skip kimage_file_post_load_cleanup(), and consequently kexec_file_post_load_cleanup_dm_crypt() as well. If that happens, the config_keys_subsys.su_mutex remains locked, which could cause problems with the next kexec load, right? - Sourabh Jain > 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)