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Wed, 02 Sep 2026 06:12:21 -0700 (PDT) From: Coiby Xu X-Google-Original-From: Coiby Xu Date: Wed, 2 Sep 2026 20:53:51 +0800 To: Jinjie Ruan Cc: kexec@lists.infradead.org, Andrew Morton , Sourabh Jain , Baoquan He , Dave Young , Pratyush Yadav , Mike Rapoport , Pasha Tatashin , open list Subject: Re: [PATCH v4 1/9] crash_dump: Fix potential double free and UAF of keys_header Message-ID: References: <20260828084900.1496839-1-coiby.xu@gmail.com> <20260828084900.1496839-2-coiby.xu@gmail.com> <76f634e3-9adb-4ae2-b2b0-a7e13a2f93c3@huawei.com> 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=utf-8; format=flowed Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Tue, Sep 01, 2026 at 09:36:10AM +0800, Jinjie Ruan wrote: > > >在 2026/8/31 21:44, Coiby Xu 写道: >> On Mon, Aug 31, 2026 at 03:39:35PM +0800, Jinjie Ruan wrote: >>> >>> >>> 在 2026/8/28 16:48, Coiby Xu 写道: >>>> 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(-) >>>> > >[...] > >>>> @@ -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; >>> >>> I think there's still a bug for arm64 here. >>> >>> When is_dm_key_reused set to true, the outer while loop prematurely >>> clears the is_dm_key_reused flag at the end of >>> crash_load_dm_crypt_keys() in the very first iteration. >>> >>> Consequently, subsequent re-entrant calls to crash_load_dm_crypt_keys() >>> falsely perceive the keys as not reused, forcing a redundant execution >>> of build_keys_header() which overwrites the global keys_header pointer; >>> >>> This induces a silent kernel memory leak. >> >> Thanks for reviewing this patch and raising the concern! Unless I miss >> something, I don't think the global keys_header will be overwritten >> because kexec_file_post_load_cleanup_dm_crypt will called to free the >> memory during the end of kexec_file_load syscall. > >Hi Coiby, Hi Jinjie, > >Not really on arm64, as below: > >kexec_file_load syscall >-> kimage_file_alloc_init() > -> kimage_file_prepare_segments() > -> kexec_image_load_default() > -> arm64 image_load() > -> load_other_segments() while retry loop > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > -> crash_load_dm_crypt_keys() -> May be called >repeatedly!!! Memory leak bug here as I described above, Thanks for providing the stack trace to help me understand the problem! Now I see what I missed. I also notice your "[PATCH v3 04/17] arm64: kexec_file: Fix elf_headers memory leak in retry loop" is addressing the same problem for the elf_headers. I'll have a careful look at related patches and re-think the solution. > > -> kimage_file_post_load_cleanup() > >> >>> >>> 92 >-------/* >>> 93 >------- * The location of the kernel segment may make it impossible >>> to satisfy >>> 94 >------- * the other segment requirements, so we try repeatedly to >>> find a >>> 95 >------- * location that will work. >>> 96 >------- */ >>> 97 >-------while ((ret = kexec_add_buffer(&kbuf)) == 0) { >>> 98 >------->-------/* Try to load additional data */ >>> 99 >------->-------kernel_segment = &image- >>> >segment[kernel_segment_number]; >>> 100 >------->-------ret = load_other_segments(image, kernel_segment->mem, >>> 101 >------->------->------->------->-------  kernel_segment->memsz, >>> initrd, >>> 102 >------->------->------->------->-------  initrd_len, cmdline); >>> 103 >------->-------if (!ret) >>> 104 >------->------->-------break; >>> 105 >>> 106 >------->-------/* >>> 107 >------->------- * We couldn't find space for the other segments; >>> erase the >>> 108 >------->------- * kernel segment and try the next available hole. >>> 109 >------->------- */ >>> 110 >------->-------image->nr_segments -= 1; >>> 111 >------->-------kbuf.buf_min = kernel_segment->mem + >>> kernel_segment->memsz; >>> 112 >------->-------kbuf.mem = KEXEC_BUF_MEM_UNKNOWN; >>> 113 >-------} >> >> Btw, I assume the above text is not related to the discussion, right? > >The code closely related to my description above — the arm64 >crash_load_dm_crypt_keys() — is exactly called within the >load_other_segments() in the while loop mentioned earlier. Therefore, >crash_load_dm_crypt_keys() may be called repeatedly before >kexec_file_post_load_cleanup_dm_crypt(). > >We can refer to the arm64 commit 108aa503657e ("arm64: kexec_file: try >more regions if loading segments fails") , which introduced the retry loop. Thanks for the explanation and also pointing me to the reference commit! > >Best regards, >Jinjie > >> [...] >> > -- Best regards, Coiby