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[46.135.27.89]) by smtp.gmail.com with ESMTPSA id y17-20020a170906525100b00992c92af6f4sm1536006ejm.144.2023.08.18.12.12.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 18 Aug 2023 12:12:42 -0700 (PDT) Date: Fri, 18 Aug 2023 21:12:39 +0200 From: Mateusz Guzik To: Kees Cook Cc: "Eric W. Biederman" , syzbot , anton@tuxera.com, brauner@kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-ntfs-dev@lists.sourceforge.net, syzkaller-bugs@googlegroups.com, viro@zeniv.linux.org.uk Subject: Re: [syzbot] [ntfs?] WARNING in do_open_execat Message-ID: <20230818191239.3cprv2wncyyy5yxj@f> References: <000000000000c74d44060334d476@google.com> <87o7j471v8.fsf@email.froward.int.ebiederm.org> <202308181030.0DA3FD14@keescook> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <202308181030.0DA3FD14@keescook> X-Stat-Signature: mpejxom499w7rfz7t7h1cpstanpby8uq X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 4DC1F8000D X-Rspam-User: X-HE-Tag: 1692385964-123061 X-HE-Meta: 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 tolJpNje 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, Aug 18, 2023 at 10:33:26AM -0700, Kees Cook wrote: > This is a double-check I left in place, since it shouldn't have been reachable: > > /* > * may_open() has already checked for this, so it should be > * impossible to trip now. But we need to be extra cautious > * and check again at the very end too. > */ > err = -EACCES; > if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode) || > path_noexec(&file->f_path))) > goto exit; > As I mentioned in my other e-mail, the check is racy -- an unlucky enough remounting with noexec should trip over it, and probably a chmod too. However, that's not what triggers the warn in this case. The ntfs image used here is intentionally corrupted and the inode at hand has a mode of 777 (as in type not specified). Then the type check in may_open(): switch (inode->i_mode & S_IFMT) { fails to match anything. This debug printk: diff --git a/fs/namei.c b/fs/namei.c index e56ff39a79bc..05652e8a1069 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -3259,6 +3259,10 @@ static int may_open(struct mnt_idmap *idmap, const struct path *path, if ((acc_mode & MAY_EXEC) && path_noexec(path)) return -EACCES; break; + default: + /* bogus mode! */ + printk(KERN_EMERG "got bogus mode inode!\n"); + return -EACCES; } error = inode_permission(idmap, inode, MAY_OPEN | acc_mode); catches it. All that said, I think adding a WARN_ONCE here is prudent, but I don't know if denying literally all opts is the way to go. Do other filesystems have provisions to prevent inodes like this from getting here?