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Thu, 25 Jun 2026 03:50:43 -0700 (PDT) From: Coiby Xu X-Google-Original-From: Coiby Xu Date: Thu, 25 Jun 2026 18:46:33 +0800 To: Guangshuo Li Cc: Andrew Morton , Baoquan He , Vivek Goyal , Dave Young , kexec@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] crash_dump: release keyring reference at the correct time Message-ID: References: <20260603135056.1397084-1-lgs201920130244@gmail.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=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20260603135056.1397084-1-lgs201920130244@gmail.com> Hi Guangshuo, Thanks for sending this patch! Your fix is more complete than my version https://lore.kernel.org/kexec/20260501234342.2518281-2-coiby.xu@gmail.com/ So I plan to drop mine from the patch set. I only have some nitpicking for this patch. Please check inline comments. On Wed, Jun 03, 2026 at 09:50:56PM +0800, Guangshuo Li wrote: >restore_dm_crypt_keys_to_thread_keyring() gets a reference to the user >keyring before restoring the saved dm-crypt keys. > >The same keyring reference is then passed to add_key_to_keyring() for each >saved key, but add_key_to_keyring() drops that reference on every call. >This is only balanced when exactly one key is restored. With multiple >keys, the keyring reference is dropped too many times and may trigger a >refcount underflow or use-after-free. My testing shows when there are more than five keys to be added, this "refcount_t: underflow; use-after" error can occur. Maybe you can include this info in your commit msg. > >The early error paths after lookup_user_key() also return without dropping >the keyring reference. > >Keep ownership of the keyring reference in >restore_dm_crypt_keys_to_thread_keyring(), drop it once on all exit paths, >and make add_key_to_keyring() only use the reference without consuming it. > >Fixes: 62f17d9df692 ("crash_dump: retrieve dm crypt keys in kdump kernel") >Signed-off-by: Guangshuo Li >--- > kernel/crash_dump_dm_crypt.c | 15 ++++++++++----- > 1 file changed, 10 insertions(+), 5 deletions(-) > >diff --git a/kernel/crash_dump_dm_crypt.c b/kernel/crash_dump_dm_crypt.c >index a20d4097744a..641c290f1270 100644 >--- a/kernel/crash_dump_dm_crypt.c >+++ b/kernel/crash_dump_dm_crypt.c >@@ -80,7 +80,6 @@ static int add_key_to_keyring(struct dm_crypt_key *dm_key, > kexec_dprintk("Error when adding key"); > } > >- key_ref_put(keyring_ref); > return r; > } > >@@ -104,6 +103,7 @@ static int restore_dm_crypt_keys_to_thread_keyring(void) > size_t keys_header_size; > key_ref_t keyring_ref; I think ordering local variables from longest line length to shortest line length a.k.a Reverse Christmas Tree style is preferred i.e. int ret = 0; u64 addr; -- Best regards, Coiby