From: Aleksa Sarai <cyphar@cyphar.com> To: Al Viro <viro@zeniv.linux.org.uk>, Jeff Layton <jlayton@kernel.org>, "J. Bruce Fields" <bfields@fieldses.org>, Arnd Bergmann <arnd@arndb.de>, David Howells <dhowells@redhat.com>, Shuah Khan <shuah@kernel.org>, Shuah Khan <skhan@linuxfoundation.org>, Ingo Molnar <mingo@redhat.com>, Peter Zijlstra <peterz@infradead.org>, Christian Brauner <christian@brauner.io> Cc: Aleksa Sarai <cyphar@cyphar.com>, Eric Biederman <ebiederm@xmission.com>, Andy Lutomirski <luto@kernel.org>, Andrew Morton <akpm@linux-foundation.org>, Alexei Starovoitov <ast@kernel.org>, Kees Cook <keescook@chromium.org>, Jann Horn <jannh@google.com>, Tycho Andersen <tycho@tycho.ws>, David Drysdale <drysdale@google.com>, Chanho Min <chanho.min@lge.com>, Oleg Nesterov <oleg@redhat.com>, Rasmus Villemoes <linux@rasmusvillemoes.dk>, Alexander Shishkin <alexander.shishkin@linux.intel.com>, Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>, Aleksa Sarai <asarai@suse.de>, Linus Torvalds <torvalds@linux-foundation.org>, containers@lists.linux-foundation.org, linux-alpha@vger.kernel.org, linux-api@vger.kernel.org, linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-ia64@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-m68k@lists.linux-m68k.org, linux-mips@vger.kernel.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, linux-xtensa@linux-xtensa.org, sparclinux@vger.kernel.org Subject: [PATCH v12 07/12] open: O_EMPTYPATH: procfs-less file descriptor re-opening Date: Thu, 5 Sep 2019 06:19:28 +1000 Message-ID: <20190904201933.10736-8-cyphar@cyphar.com> (raw) In-Reply-To: <20190904201933.10736-1-cyphar@cyphar.com> Userspace has made use of /proc/self/fd very liberally to allow for descriptors to be re-opened. There are a wide variety of uses for this feature, but it has always required constructing a pathname and could not be done without procfs mounted. The obvious solution for this is to extend openat(2) to have an AT_EMPTY_PATH-equivalent -- O_EMPTYPATH. Now that descriptor re-opening has been made safe through the new magic-link resolution restrictions, we can replicate these restrictions for O_EMPTYPATH. In particular, we only allow "upgrading" the file descriptor if the corresponding FMODE_PATH_* bit is set (or the FMODE_{READ,WRITE} cases for non-O_PATH file descriptors). When doing openat(O_EMPTYPATH|O_PATH), O_PATH takes precedence and O_EMPTYPATH is ignored. Very few users ever have a need to O_PATH re-open an existing file descriptor, and so accommodating them at the expense of further complicating O_PATH makes little sense. Ultimately, if users ask for this we can always add RESOLVE_EMPTY_PATH to resolveat(2) in the future. Signed-off-by: Aleksa Sarai <cyphar@cyphar.com> --- arch/alpha/include/uapi/asm/fcntl.h | 1 + arch/parisc/include/uapi/asm/fcntl.h | 39 ++++++++++++++-------------- arch/sparc/include/uapi/asm/fcntl.h | 1 + fs/fcntl.c | 2 +- fs/namei.c | 20 ++++++++++++++ fs/open.c | 7 ++++- include/linux/fcntl.h | 2 +- include/uapi/asm-generic/fcntl.h | 4 +++ 8 files changed, 54 insertions(+), 22 deletions(-) diff --git a/arch/alpha/include/uapi/asm/fcntl.h b/arch/alpha/include/uapi/asm/fcntl.h index 50bdc8e8a271..1f879bade68b 100644 --- a/arch/alpha/include/uapi/asm/fcntl.h +++ b/arch/alpha/include/uapi/asm/fcntl.h @@ -34,6 +34,7 @@ #define O_PATH 040000000 #define __O_TMPFILE 0100000000 +#define O_EMPTYPATH 0200000000 #define F_GETLK 7 #define F_SETLK 8 diff --git a/arch/parisc/include/uapi/asm/fcntl.h b/arch/parisc/include/uapi/asm/fcntl.h index 03ce20e5ad7d..5d709058a76f 100644 --- a/arch/parisc/include/uapi/asm/fcntl.h +++ b/arch/parisc/include/uapi/asm/fcntl.h @@ -2,26 +2,27 @@ #ifndef _PARISC_FCNTL_H #define _PARISC_FCNTL_H -#define O_APPEND 000000010 -#define O_BLKSEEK 000000100 /* HPUX only */ -#define O_CREAT 000000400 /* not fcntl */ -#define O_EXCL 000002000 /* not fcntl */ -#define O_LARGEFILE 000004000 -#define __O_SYNC 000100000 +#define O_APPEND 0000000010 +#define O_BLKSEEK 0000000100 /* HPUX only */ +#define O_CREAT 0000000400 /* not fcntl */ +#define O_EXCL 0000002000 /* not fcntl */ +#define O_LARGEFILE 0000004000 +#define __O_SYNC 0000100000 #define O_SYNC (__O_SYNC|O_DSYNC) -#define O_NONBLOCK 000200004 /* HPUX has separate NDELAY & NONBLOCK */ -#define O_NOCTTY 000400000 /* not fcntl */ -#define O_DSYNC 001000000 /* HPUX only */ -#define O_RSYNC 002000000 /* HPUX only */ -#define O_NOATIME 004000000 -#define O_CLOEXEC 010000000 /* set close_on_exec */ - -#define O_DIRECTORY 000010000 /* must be a directory */ -#define O_NOFOLLOW 000000200 /* don't follow links */ -#define O_INVISIBLE 004000000 /* invisible I/O, for DMAPI/XDSM */ - -#define O_PATH 020000000 -#define __O_TMPFILE 040000000 +#define O_NONBLOCK 0000200004 /* HPUX has separate NDELAY & NONBLOCK */ +#define O_NOCTTY 0000400000 /* not fcntl */ +#define O_DSYNC 0001000000 /* HPUX only */ +#define O_RSYNC 0002000000 /* HPUX only */ +#define O_NOATIME 0004000000 +#define O_CLOEXEC 0010000000 /* set close_on_exec */ + +#define O_DIRECTORY 0000010000 /* must be a directory */ +#define O_NOFOLLOW 0000000200 /* don't follow links */ +#define O_INVISIBLE 0004000000 /* invisible I/O, for DMAPI/XDSM */ + +#define O_PATH 0020000000 +#define __O_TMPFILE 0040000000 +#define O_EMPTYPATH 0100000000 #define F_GETLK64 8 #define F_SETLK64 9 diff --git a/arch/sparc/include/uapi/asm/fcntl.h b/arch/sparc/include/uapi/asm/fcntl.h index 67dae75e5274..dc86c9eaf950 100644 --- a/arch/sparc/include/uapi/asm/fcntl.h +++ b/arch/sparc/include/uapi/asm/fcntl.h @@ -37,6 +37,7 @@ #define O_PATH 0x1000000 #define __O_TMPFILE 0x2000000 +#define O_EMPTYPATH 0x4000000 #define F_GETOWN 5 /* for sockets. */ #define F_SETOWN 6 /* for sockets. */ diff --git a/fs/fcntl.c b/fs/fcntl.c index 3d40771e8e7c..4cf05a2fd162 100644 --- a/fs/fcntl.c +++ b/fs/fcntl.c @@ -1031,7 +1031,7 @@ static int __init fcntl_init(void) * Exceptions: O_NONBLOCK is a two bit define on parisc; O_NDELAY * is defined as O_NONBLOCK on some platforms and not on others. */ - BUILD_BUG_ON(21 - 1 /* for O_RDONLY being 0 */ != + BUILD_BUG_ON(22 - 1 /* for O_RDONLY being 0 */ != HWEIGHT32( (VALID_OPEN_FLAGS & ~(O_NONBLOCK | O_NDELAY)) | __FMODE_EXEC | __FMODE_NONOTIFY)); diff --git a/fs/namei.c b/fs/namei.c index 54d57dad0f91..e39b573fcc4d 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -3571,6 +3571,24 @@ static int trailing_magiclink(struct nameidata *nd, int acc_mode, return may_open_magiclink(upgrade_mask, acc_mode); } +static int do_emptypath(struct nameidata *nd, const struct open_flags *op, + struct file *file) +{ + int error; + /* We don't support AT_FDCWD (since O_PATH is disallowed here). */ + struct fd f = fdget_raw(nd->dfd); + + if (!f.file) + return -EBADF; + + /* Apply trailing_magiclink()-like restrictions. */ + error = may_open_magiclink(f.file->f_mode, op->acc_mode); + if (!error) + error = vfs_open(&f.file->f_path, file); + fdput(f); + return error; +} + static struct file *path_openat(struct nameidata *nd, const struct open_flags *op, unsigned flags) { @@ -3583,6 +3601,8 @@ static struct file *path_openat(struct nameidata *nd, if (unlikely(file->f_flags & __O_TMPFILE)) { error = do_tmpfile(nd, flags, op, file); + } else if (unlikely(file->f_flags & O_EMPTYPATH)) { + error = do_emptypath(nd, op, file); } else if (unlikely(file->f_flags & O_PATH)) { /* Inlined path_lookupat() with a trailing_magiclink() check. */ fmode_t opath_mask = op->opath_mask; diff --git a/fs/open.c b/fs/open.c index 806a75d685e1..310b896eecf0 100644 --- a/fs/open.c +++ b/fs/open.c @@ -1015,6 +1015,8 @@ static inline int build_open_flags(int flags, umode_t mode, struct open_flags *o lookup_flags |= LOOKUP_DIRECTORY; if (!(flags & O_NOFOLLOW)) lookup_flags |= LOOKUP_FOLLOW; + if (flags & O_EMPTYPATH) + lookup_flags |= LOOKUP_EMPTY; op->lookup_flags = lookup_flags; return 0; } @@ -1076,14 +1078,17 @@ long do_sys_open(int dfd, const char __user *filename, int flags, umode_t mode) { struct open_flags op; int fd = build_open_flags(flags, mode, &op); + int empty = 0; struct filename *tmp; if (fd) return fd; - tmp = getname(filename); + tmp = getname_flags(filename, op.lookup_flags, &empty); if (IS_ERR(tmp)) return PTR_ERR(tmp); + if (!empty) + op.open_flag &= ~O_EMPTYPATH; fd = get_unused_fd_flags(flags); if (fd >= 0) { diff --git a/include/linux/fcntl.h b/include/linux/fcntl.h index d019df946cb2..2868ae6c8fc1 100644 --- a/include/linux/fcntl.h +++ b/include/linux/fcntl.h @@ -9,7 +9,7 @@ (O_RDONLY | O_WRONLY | O_RDWR | O_CREAT | O_EXCL | O_NOCTTY | O_TRUNC | \ O_APPEND | O_NDELAY | O_NONBLOCK | O_NDELAY | __O_SYNC | O_DSYNC | \ FASYNC | O_DIRECT | O_LARGEFILE | O_DIRECTORY | O_NOFOLLOW | \ - O_NOATIME | O_CLOEXEC | O_PATH | __O_TMPFILE) + O_NOATIME | O_CLOEXEC | O_PATH | __O_TMPFILE | O_EMPTYPATH) #ifndef force_o_largefile #define force_o_largefile() (!IS_ENABLED(CONFIG_ARCH_32BIT_OFF_T)) diff --git a/include/uapi/asm-generic/fcntl.h b/include/uapi/asm-generic/fcntl.h index 9dc0bf0c5a6e..ae6862f69cc2 100644 --- a/include/uapi/asm-generic/fcntl.h +++ b/include/uapi/asm-generic/fcntl.h @@ -89,6 +89,10 @@ #define __O_TMPFILE 020000000 #endif +#ifndef O_EMPTYPATH +#define O_EMPTYPATH 040000000 +#endif + /* a horrid kludge trying to make sure that this will fail on old kernels */ #define O_TMPFILE (__O_TMPFILE | O_DIRECTORY) #define O_TMPFILE_MASK (__O_TMPFILE | O_DIRECTORY | O_CREAT) -- 2.23.0
next prev parent reply index Thread overview: 65+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-09-04 20:19 [PATCH v12 00/12] namei: openat2(2) path resolution restrictions Aleksa Sarai 2019-09-04 20:19 ` [PATCH v12 01/12] lib: introduce copy_struct_{to,from}_user helpers Aleksa Sarai 2019-09-04 20:48 ` Linus Torvalds 2019-09-04 21:00 ` Randy Dunlap 2019-09-05 7:32 ` Peter Zijlstra 2019-09-05 9:26 ` Aleksa Sarai 2019-09-05 9:43 ` Peter Zijlstra 2019-09-05 10:57 ` Peter Zijlstra 2019-09-11 10:37 ` Aleksa Sarai 2019-09-05 13:35 ` Aleksa Sarai 2019-09-05 17:01 ` Aleksa Sarai 2019-09-05 8:43 ` Rasmus Villemoes 2019-09-05 9:50 ` Aleksa Sarai 2019-09-05 10:45 ` Christian Brauner 2019-09-05 9:09 ` Andreas Schwab 2019-09-05 10:13 ` [PATCH v12 01/12] lib: introduce copy_struct_{to, from}_user helpers Gabriel Paubert 2019-09-05 11:05 ` [PATCH v12 01/12] lib: introduce copy_struct_{to,from}_user helpers Christian Brauner 2019-09-05 11:17 ` Rasmus Villemoes 2019-09-05 11:29 ` Christian Brauner 2019-09-05 13:40 ` Aleksa Sarai 2019-09-05 11:09 ` Christian Brauner 2019-09-05 11:27 ` Aleksa Sarai 2019-09-05 11:40 ` Christian Brauner 2019-09-05 18:07 ` Al Viro 2019-09-05 18:23 ` Christian Brauner 2019-09-05 18:28 ` Al Viro 2019-09-05 18:35 ` Christian Brauner 2019-09-05 19:56 ` Aleksa Sarai 2019-09-05 22:31 ` Al Viro 2019-09-06 7:00 ` Christian Brauner 2019-09-05 23:00 ` Aleksa Sarai 2019-09-05 23:49 ` Al Viro 2019-09-06 0:09 ` Aleksa Sarai 2019-09-06 0:14 ` Al Viro 2019-09-04 20:19 ` [PATCH v12 02/12] clone3: switch to copy_struct_from_user() Aleksa Sarai 2019-09-04 20:19 ` [PATCH v12 03/12] sched_setattr: switch to copy_struct_{to,from}_user() Aleksa Sarai 2019-09-04 20:19 ` [PATCH v12 04/12] perf_event_open: switch to copy_struct_from_user() Aleksa Sarai 2019-09-04 20:19 ` [PATCH v12 05/12] namei: obey trailing magic-link DAC permissions Aleksa Sarai 2019-09-17 21:30 ` Jann Horn 2019-09-18 13:51 ` Aleksa Sarai 2019-09-18 15:46 ` Aleksa Sarai 2019-09-04 20:19 ` [PATCH v12 06/12] procfs: switch magic-link modes to be more sane Aleksa Sarai 2019-09-04 20:19 ` Aleksa Sarai [this message] 2019-09-04 20:19 ` [PATCH v12 08/12] namei: O_BENEATH-style path resolution flags Aleksa Sarai 2019-09-04 20:19 ` [PATCH v12 09/12] namei: LOOKUP_IN_ROOT: chroot-like path resolution Aleksa Sarai 2019-09-04 20:19 ` [PATCH v12 10/12] namei: aggressively check for nd->root escape on ".." resolution Aleksa Sarai 2019-09-04 21:09 ` Linus Torvalds 2019-09-04 21:35 ` Linus Torvalds 2019-09-04 21:36 ` Linus Torvalds 2019-09-04 21:48 ` Aleksa Sarai 2019-09-04 22:16 ` Linus Torvalds 2019-09-04 22:31 ` David Howells 2019-09-04 22:38 ` Linus Torvalds 2019-09-04 23:29 ` Al Viro 2019-09-04 23:44 ` Linus Torvalds 2019-09-04 20:19 ` [PATCH v12 11/12] open: openat2(2) syscall Aleksa Sarai 2019-09-04 21:00 ` Randy Dunlap 2019-09-07 12:40 ` Jeff Layton 2019-09-07 16:58 ` Linus Torvalds 2019-09-07 17:42 ` Andy Lutomirski 2019-09-07 17:45 ` Linus Torvalds 2019-09-07 18:15 ` Andy Lutomirski 2019-09-10 6:35 ` Ingo Molnar 2019-09-08 16:24 ` Aleksa Sarai 2019-09-04 20:19 ` [PATCH v12 12/12] selftests: add openat2(2) selftests Aleksa Sarai
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