vfs: add faccessat2 syscall

POSIX defines faccessat() as having a fourth "flags" argument, while the linux syscall doesn't have it. Glibc tries to emulate AT_EACCESS and AT_SYMLINK_NOFOLLOW, but AT_EACCESS emulation is broken. Add a new faccessat(2) syscall with the added flags argument and implement both flags. The value of AT_EACCESS is defined in glibc headers to be the same as AT_REMOVEDIR. Use this value for the kernel interface as well, together with the explanatory comment. Also add AT_EMPTY_PATH support, which is not documented by POSIX, but can be useful and is trivial to implement.

Miklos Szeredi committed 6 years ago

Commit c8ffd8b1 parent 55923e423 files · +62 −13Browse files

Unified · Split

23 files

arch/alpha/kernel/syscalls/syscall.tbl +1 −0
arch/arm/tools/syscall.tbl +1 −0
arch/arm64/include/asm/unistd.h +1 −1
arch/arm64/include/asm/unistd32.h +2 −0
arch/ia64/kernel/syscalls/syscall.tbl +1 −0
arch/m68k/kernel/syscalls/syscall.tbl +1 −0
arch/microblaze/kernel/syscalls/syscall.tbl +1 −0
arch/mips/kernel/syscalls/syscall_n32.tbl +1 −0
arch/mips/kernel/syscalls/syscall_n64.tbl +1 −0
arch/mips/kernel/syscalls/syscall_o32.tbl +1 −0
arch/parisc/kernel/syscalls/syscall.tbl +1 −0
arch/powerpc/kernel/syscalls/syscall.tbl +1 −0
arch/s390/kernel/syscalls/syscall.tbl +1 −0
arch/sh/kernel/syscalls/syscall.tbl +1 −0
arch/sparc/kernel/syscalls/syscall.tbl +1 −0
arch/x86/entry/syscalls/syscall_32.tbl +1 −0
arch/x86/entry/syscalls/syscall_64.tbl +1 −0
arch/xtensa/kernel/syscalls/syscall.tbl +1 −0
fs/internal.h +0 −1
fs/open.c +26 −8
include/linux/syscalls.h +4 −2
include/uapi/asm-generic/unistd.h +3 −1
include/uapi/linux/fcntl.h +10 −0

arch/alpha/kernel/syscalls/syscall.tbl+1−0

@@ -477,3 +477,4 @@ · 476 unmodified lines
477	477	# 545 reserved for clone3
478	478	547 common openat2 sys_openat2
479	479	548 common pidfd_getfd sys_pidfd_getfd
	480	+549 common faccessat2 sys_faccessat2

arch/arm/tools/syscall.tbl+1−0

@@ -451,3 +451,4 @@ · 450 unmodified lines
451	451	435 common clone3 sys_clone3
452	452	437 common openat2 sys_openat2
453	453	438 common pidfd_getfd sys_pidfd_getfd
	454	+439 common faccessat2 sys_faccessat2

arch/arm64/include/asm/unistd.h+1−1

@@ -38,7 +38,7 @@ · 37 unmodified lines
38	38	#define __ARM_NR_compat_set_tls (__ARM_NR_COMPAT_BASE + 5)
39	39	#define __ARM_NR_COMPAT_END (__ARM_NR_COMPAT_BASE + 0x800)
40	40
41		−#define __NR_compat_syscalls 439
	41	+#define __NR_compat_syscalls 440
42	42	#endif
43	43
44	44	#define __ARCH_WANT_SYS_CLONE

arch/arm64/include/asm/unistd32.h+2−0

@@ -883,6 +883,8 @@ __SYSCALL(__NR_clone3, sys_clone3) · 882 unmodified lines
883	883	__SYSCALL(__NR_openat2, sys_openat2)
884	884	#define __NR_pidfd_getfd 438
885	885	__SYSCALL(__NR_pidfd_getfd, sys_pidfd_getfd)
	886	+#define __NR_faccessat2 439
	887	+__SYSCALL(__NR_faccessat2, sys_faccessat2)
886	888
887	889	/*
888	890	* Please add new compat syscalls above this comment and update

arch/ia64/kernel/syscalls/syscall.tbl+1−0

@@ -358,3 +358,4 @@ · 357 unmodified lines
358	358	# 435 reserved for clone3
359	359	437 common openat2 sys_openat2
360	360	438 common pidfd_getfd sys_pidfd_getfd
	361	+439 common faccessat2 sys_faccessat2

arch/m68k/kernel/syscalls/syscall.tbl+1−0

@@ -437,3 +437,4 @@ · 436 unmodified lines
437	437	435 common clone3 __sys_clone3
438	438	437 common openat2 sys_openat2
439	439	438 common pidfd_getfd sys_pidfd_getfd
	440	+439 common faccessat2 sys_faccessat2

arch/microblaze/kernel/syscalls/syscall.tbl+1−0

@@ -443,3 +443,4 @@ · 442 unmodified lines
443	443	435 common clone3 sys_clone3
444	444	437 common openat2 sys_openat2
445	445	438 common pidfd_getfd sys_pidfd_getfd
	446	+439 common faccessat2 sys_faccessat2

arch/mips/kernel/syscalls/syscall_n32.tbl+1−0

@@ -376,3 +376,4 @@ · 375 unmodified lines
376	376	435 n32 clone3 __sys_clone3
377	377	437 n32 openat2 sys_openat2
378	378	438 n32 pidfd_getfd sys_pidfd_getfd
	379	+439 n32 faccessat2 sys_faccessat2

arch/mips/kernel/syscalls/syscall_n64.tbl+1−0

@@ -352,3 +352,4 @@ · 351 unmodified lines
352	352	435 n64 clone3 __sys_clone3
353	353	437 n64 openat2 sys_openat2
354	354	438 n64 pidfd_getfd sys_pidfd_getfd
	355	+439 n64 faccessat2 sys_faccessat2

arch/mips/kernel/syscalls/syscall_o32.tbl+1−0

@@ -425,3 +425,4 @@ · 424 unmodified lines
425	425	435 o32 clone3 __sys_clone3
426	426	437 o32 openat2 sys_openat2
427	427	438 o32 pidfd_getfd sys_pidfd_getfd
	428	+439 o32 faccessat2 sys_faccessat2

arch/parisc/kernel/syscalls/syscall.tbl+1−0

@@ -435,3 +435,4 @@ · 434 unmodified lines
435	435	435 common clone3 sys_clone3_wrapper
436	436	437 common openat2 sys_openat2
437	437	438 common pidfd_getfd sys_pidfd_getfd
	438	+439 common faccessat2 sys_faccessat2

arch/powerpc/kernel/syscalls/syscall.tbl+1−0

@@ -527,3 +527,4 @@ · 526 unmodified lines
527	527	435 spu clone3 sys_ni_syscall
528	528	437 common openat2 sys_openat2
529	529	438 common pidfd_getfd sys_pidfd_getfd
	530	+439 common faccessat2 sys_faccessat2

arch/s390/kernel/syscalls/syscall.tbl+1−0

@@ -440,3 +440,4 @@ · 439 unmodified lines
440	440	435 common clone3 sys_clone3 sys_clone3
441	441	437 common openat2 sys_openat2 sys_openat2
442	442	438 common pidfd_getfd sys_pidfd_getfd sys_pidfd_getfd
	443	+439 common faccessat2 sys_faccessat2 sys_faccessat2

arch/sh/kernel/syscalls/syscall.tbl+1−0

@@ -440,3 +440,4 @@ · 439 unmodified lines
440	440	# 435 reserved for clone3
441	441	437 common openat2 sys_openat2
442	442	438 common pidfd_getfd sys_pidfd_getfd
	443	+439 common faccessat2 sys_faccessat2

arch/sparc/kernel/syscalls/syscall.tbl+1−0

@@ -483,3 +483,4 @@ · 482 unmodified lines
483	483	# 435 reserved for clone3
484	484	437 common openat2 sys_openat2
485	485	438 common pidfd_getfd sys_pidfd_getfd
	486	+439 common faccessat2 sys_faccessat2

arch/x86/entry/syscalls/syscall_32.tbl+1−0

@@ -442,3 +442,4 @@ · 441 unmodified lines
442	442	435 i386 clone3 sys_clone3
443	443	437 i386 openat2 sys_openat2
444	444	438 i386 pidfd_getfd sys_pidfd_getfd
	445	+439 i386 faccessat2 sys_faccessat2

arch/x86/entry/syscalls/syscall_64.tbl+1−0

@@ -359,6 +359,7 @@ · 358 unmodified lines
359	359	435 common clone3 sys_clone3
360	360	437 common openat2 sys_openat2
361	361	438 common pidfd_getfd sys_pidfd_getfd
	362	+439 common faccessat2 sys_faccessat2
362	363
363	364	#
364	365	# x32-specific system call numbers start at 512 to avoid cache impact

arch/xtensa/kernel/syscalls/syscall.tbl+1−0

@@ -408,3 +408,4 @@ · 407 unmodified lines
408	408	435 common clone3 sys_clone3
409	409	437 common openat2 sys_openat2
410	410	438 common pidfd_getfd sys_pidfd_getfd
	411	+439 common faccessat2 sys_faccessat2

fs/internal.h+0−1

@@ -126,7 +126,6 @@ extern struct open_how build_open_how(int flags, umode_t mode); · 125 unmodified lines
126	126	extern int build_open_flags(const struct open_how how, struct open_flags op);
127	127
128	128	long do_sys_ftruncate(unsigned int fd, loff_t length, int small);
129		−long do_faccessat(int dfd, const char __user *filename, int mode);
130	129	int do_fchmodat(int dfd, const char __user *filename, umode_t mode);
131	130	int do_fchownat(int dfd, const char __user *filename, uid_t user, gid_t group,
132	131	int flag);

fs/open.c+26−8

@@ -394,20 +394,30 @@ static const struct cred *access_override_creds(void) · 393 unmodified lines
394	394	return old_cred;
395	395	}
396	396
397		−long do_faccessat(int dfd, const char __user *filename, int mode)
	397	+long do_faccessat(int dfd, const char __user *filename, int mode, int flags)
398	398	{
399	399	struct path path;
400	400	struct inode *inode;
401	401	int res;
402	402	unsigned int lookup_flags = LOOKUP_FOLLOW;
403		− const struct cred *old_cred;
	403	+ const struct cred *old_cred = NULL;
404	404
405	405	if (mode & ~S_IRWXO) /* where's F_OK, X_OK, W_OK, R_OK? */
406	406	return -EINVAL;
407	407
408		− old_cred = access_override_creds();
409		− if (!old_cred)
410		− return -ENOMEM;
	408	+ if (flags & ~(AT_EACCESS \| AT_SYMLINK_NOFOLLOW \| AT_EMPTY_PATH))
	409	+ return -EINVAL;
	410	+
	411	+ if (flags & AT_SYMLINK_NOFOLLOW)
	412	+ lookup_flags &= ~LOOKUP_FOLLOW;
	413	+ if (flags & AT_EMPTY_PATH)
	414	+ lookup_flags \|= LOOKUP_EMPTY;
	415	+
	416	+ if (!(flags & AT_EACCESS)) {
	417	+ old_cred = access_override_creds();
	418	+ if (!old_cred)
	419	+ return -ENOMEM;
	420	+ }
411	421
412	422	retry:
413	423	res = user_path_at(dfd, filename, lookup_flags, &path);
@@ -450,18 +460,26 @@ out_path_release: · 36 unmodified lines
450	460	goto retry;
451	461	}
452	462	out:
453		− revert_creds(old_cred);
	463	+ if (old_cred)
	464	+ revert_creds(old_cred);
	465	+
454	466	return res;
455	467	}
456	468
457	469	SYSCALL_DEFINE3(faccessat, int, dfd, const char __user *, filename, int, mode)
458	470	{
459		− return do_faccessat(dfd, filename, mode);
	471	+ return do_faccessat(dfd, filename, mode, 0);
	472	+}
	473	+
	474	+SYSCALL_DEFINE4(faccessat2, int, dfd, const char __user *, filename, int, mode,
	475	+ int, flags)
	476	+{
	477	+ return do_faccessat(dfd, filename, mode, flags);
460	478	}
461	479
462	480	SYSCALL_DEFINE2(access, const char __user *, filename, int, mode)
463	481	{
464		− return do_faccessat(AT_FDCWD, filename, mode);
	482	+ return do_faccessat(AT_FDCWD, filename, mode, 0);
465	483	}
466	484
467	485	int ksys_chdir(const char __user *filename)

include/linux/syscalls.h+4−2

@@ -428,6 +428,8 @@ asmlinkage long sys_ftruncate64(unsigned int fd, loff_t length); · 427 unmodified lines
428	428	#endif
429	429	asmlinkage long sys_fallocate(int fd, int mode, loff_t offset, loff_t len);
430	430	asmlinkage long sys_faccessat(int dfd, const char __user *filename, int mode);
	431	+asmlinkage long sys_faccessat2(int dfd, const char __user *filename, int mode,
	432	+ int flags);
431	433	asmlinkage long sys_chdir(const char __user *filename);
432	434	asmlinkage long sys_fchdir(unsigned int fd);
433	435	asmlinkage long sys_chroot(const char __user *filename);
@@ -1333,11 +1335,11 @@ static inline int ksys_chmod(const char __user *filename, umode_t mode) · 899 unmodified lines
1333	1335	return do_fchmodat(AT_FDCWD, filename, mode);
1334	1336	}
1335	1337
1336		−extern long do_faccessat(int dfd, const char __user *filename, int mode);
	1338	+long do_faccessat(int dfd, const char __user *filename, int mode, int flags);
1337	1339
1338	1340	static inline long ksys_access(const char __user *filename, int mode)
1339	1341	{
1340		− return do_faccessat(AT_FDCWD, filename, mode);
	1342	+ return do_faccessat(AT_FDCWD, filename, mode, 0);
1341	1343	}
1342	1344
1343	1345	extern int do_fchownat(int dfd, const char __user *filename, uid_t user,

include/uapi/asm-generic/unistd.h+3−1

@@ -855,9 +855,11 @@ __SYSCALL(__NR_clone3, sys_clone3) · 854 unmodified lines
855	855	__SYSCALL(__NR_openat2, sys_openat2)
856	856	#define __NR_pidfd_getfd 438
857	857	__SYSCALL(__NR_pidfd_getfd, sys_pidfd_getfd)
	858	+#define __NR_faccessat2 439
	859	+__SYSCALL(__NR_faccessat2, sys_faccessat2)
858	860
859	861	#undef __NR_syscalls
860		−#define __NR_syscalls 439
	862	+#define __NR_syscalls 440
861	863
862	864	/*
863	865	* 32 bit systems traditionally used different

include/uapi/linux/fcntl.h+10−0

@@ -84,10 +84,20 @@ · 83 unmodified lines
84	84	#define DN_ATTRIB 0x00000020 /* File changed attibutes */
85	85	#define DN_MULTISHOT 0x80000000 /* Don't remove notifier */
86	86
	87	+/*
	88	+ * The constants AT_REMOVEDIR and AT_EACCESS have the same value. AT_EACCESS is
	89	+ * meaningful only to faccessat, while AT_REMOVEDIR is meaningful only to
	90	+ * unlinkat. The two functions do completely different things and therefore,
	91	+ * the flags can be allowed to overlap. For example, passing AT_REMOVEDIR to
	92	+ * faccessat would be undefined behavior and thus treating it equivalent to
	93	+ * AT_EACCESS is valid undefined behavior.
	94	+ */
87	95	#define AT_FDCWD -100 /* Special value used to indicate
88	96	openat should use the current
89	97	working directory. */
90	98	#define AT_SYMLINK_NOFOLLOW 0x100 /* Do not follow symbolic links. */
	99	+#define AT_EACCESS 0x200 /* Test access permitted for
	100	+ effective IDs, not real IDs. */
91	101	#define AT_REMOVEDIR 0x200 /* Remove directory instead of
92	102	unlinking file. */
93	103	#define AT_SYMLINK_FOLLOW 0x400 /* Follow symbolic links. */