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Fri, 28 Aug 2026 01:49:08 -0700 (PDT) From: Coiby Xu To: kexec@lists.infradead.org Cc: Andrew Morton , Sourabh Jain , Baoquan He , Dave Young , Pratyush Yadav , Mike Rapoport , Pasha Tatashin , linux-kernel@vger.kernel.org (open list) Subject: [PATCH v4 1/9] crash_dump: Fix potential double free and UAF of keys_header Date: Fri, 28 Aug 2026 16:48:47 +0800 Message-ID: <20260828084900.1496839-2-coiby.xu@gmail.com> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260828084900.1496839-1-coiby.xu@gmail.com> References: <20260828084900.1496839-1-coiby.xu@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit If kexec_add_buffer somehow fails, keys_header will be freed. Depending on /sys/kernel/config/crash_dm_crypt_key/reuse, it will lead to the following two problems if the kexec_file_load syscall is called again, 1. Double free of keys_header if reuse=false 2. UAF of keys_header if reuse=true To address these problems and also make it easier to reason about the code, keep two invariants, 1. keys_header will always be freed at the end of kexec_file_load syscall except during kdump image unloading for CPU/memory hot-plugging support 2. There will always be valid keys_header if reuse=true Fixes: 479e58549b0f ("crash_dump: store dm crypt keys in kdump reserved memory") Fixes: 9ebfa8dcaea7 ("crash_dump: reuse saved dm crypt keys for CPU/memory hot-plugging") Reported-by: Sourabh Jain Signed-off-by: Coiby Xu --- include/linux/kexec.h | 6 ++++ kernel/crash_dump_dm_crypt.c | 66 ++++++++++++++++++++++++++---------- kernel/kexec_file.c | 2 ++ 3 files changed, 56 insertions(+), 18 deletions(-) diff --git a/include/linux/kexec.h b/include/linux/kexec.h index 0af8ae4fdd08..0fa8bac04576 100644 --- a/include/linux/kexec.h +++ b/include/linux/kexec.h @@ -552,6 +552,12 @@ void set_kexec_sig_enforced(void); static inline void set_kexec_sig_enforced(void) {} #endif +#ifdef CONFIG_CRASH_DM_CRYPT +void kexec_file_post_load_cleanup_dm_crypt(struct kimage *image); +#else +static inline void kexec_file_post_load_cleanup_dm_crypt(struct kimage *image) {} +#endif + #endif /* !defined(__ASSEBMLY__) */ #endif /* LINUX_KEXEC_H */ diff --git a/kernel/crash_dump_dm_crypt.c b/kernel/crash_dump_dm_crypt.c index c685497cd470..4335b6cb1fc4 100644 --- a/kernel/crash_dump_dm_crypt.c +++ b/kernel/crash_dump_dm_crypt.c @@ -84,18 +84,25 @@ static int add_key_to_keyring(struct dm_crypt_key *dm_key, return r; } -static void get_keys_from_kdump_reserved_memory(void) +static int get_keys_from_kdump_reserved_memory(void) { struct keys_header *keys_header_loaded; + size_t keys_header_size; - arch_kexec_unprotect_crashkres(); + keys_header_size = get_keys_header_size(key_count); + keys_header = kzalloc(keys_header_size, GFP_KERNEL); + if (!keys_header) + return -ENOMEM; + arch_kexec_unprotect_crashkres(); keys_header_loaded = kmap_local_page(pfn_to_page( kexec_crash_image->dm_crypt_keys_addr >> PAGE_SHIFT)); - memcpy(keys_header, keys_header_loaded, get_keys_header_size(key_count)); + memcpy(keys_header, keys_header_loaded, keys_header_size); kunmap_local(keys_header_loaded); arch_kexec_protect_crashkres(); + + return 0; } static int restore_dm_crypt_keys_to_thread_keyring(void) @@ -286,17 +293,28 @@ 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) { + bool val; + int r; + 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; } - if (kstrtobool(page, &is_dm_key_reused)) + if (kstrtobool(page, &val) || !val) return -EINVAL; - if (is_dm_key_reused) - get_keys_from_kdump_reserved_memory(); + if (is_dm_key_reused) { + pr_info("Already got dm-crypt keys, please continue with kexec_file_load syscall\n"); + } else { + r = get_keys_from_kdump_reserved_memory(); + if (r) { + pr_warn("Failed to get dm-crypt keys from reserved memory\n"); + return r; + } + is_dm_key_reused = true; + } return count; } @@ -369,9 +387,6 @@ static int build_keys_header(void) struct config_key *key; int i, r; - if (keys_header != NULL) - kvfree(keys_header); - keys_header = kzalloc(get_keys_header_size(key_count), GFP_KERNEL); if (!keys_header) return -ENOMEM; @@ -415,8 +430,7 @@ int crash_load_dm_crypt_keys(struct kimage *image) .top_down = false, .random = true, }; - int r; - + int r = 0; if (key_count <= 0) { kexec_dprintk("No dm-crypt keys\n"); @@ -424,14 +438,15 @@ int crash_load_dm_crypt_keys(struct kimage *image) } if (!is_dm_key_reused) { - image->dm_crypt_keys_addr = 0; r = build_keys_header(); - if (r) { - pr_err("Failed to build dm-crypt keys header, ret=%d\n", r); - return r; - } + if (r) + goto out; } + /* + * keys_header will be copied to reserver memory later and then be + * cleaned up at the end of kexec_file_load syscall + */ kbuf.buffer = keys_header; kbuf.bufsz = get_keys_header_size(key_count); @@ -441,18 +456,33 @@ int crash_load_dm_crypt_keys(struct kimage *image) r = kexec_add_buffer(&kbuf); if (r) { pr_err("Failed to call kexec_add_buffer, ret=%d\n", r); - kvfree((void *)kbuf.buffer); - return r; + goto out; } + image->dm_crypt_keys_addr = kbuf.mem; image->dm_crypt_keys_sz = kbuf.bufsz; kexec_dprintk( "Loaded dm crypt keys to kexec_buffer bufsz=0x%lx memsz=0x%lx\n", kbuf.bufsz, kbuf.memsz); +out: + is_dm_key_reused = false; return r; } +void kexec_file_post_load_cleanup_dm_crypt(struct kimage *image) +{ + /* + * For CPU/memory hot-plugging, the kdump image will be reloaded. Prevent + * keys_header from being cleaned up during unloading when + * is_dm_key_reused=true + */ + if (!is_dm_key_reused) { + kfree_sensitive(keys_header); + keys_header = NULL; + } +} + static int __init configfs_dmcrypt_keys_init(void) { int ret; diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c index 59fb9d71e9d8..062f7e79016d 100644 --- a/kernel/kexec_file.c +++ b/kernel/kexec_file.c @@ -140,6 +140,8 @@ void kimage_file_post_load_cleanup(struct kimage *image) kfree(image->image_loader_data); image->image_loader_data = NULL; + kexec_file_post_load_cleanup_dm_crypt(image); + kexec_file_dbg_print = false; } -- 2.55.0