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From 9621618c701a2d5eb3e26f40c68354d4dfb8f872 Mon Sep 17 00:00:00 2001
From: Andre McCurdy <armccurdy@gmail.com>
Date: Tue, 10 Oct 2017 14:33:30 -0700
Subject: [PATCH 12/12] don't pass AT_SYMLINK_NOFOLLOW flag to faccessat()
Avoid using AT_SYMLINK_NOFOLLOW flag. It doesn't seem like the right
thing to do and it's not portable (not supported by musl). See:
http://lists.landley.net/pipermail/toybox-landley.net/2014-September/003610.html
http://www.openwall.com/lists/musl/2015/02/05/2
Note that laccess() is never passing AT_EACCESS so a lot of the
discussion in the links above doesn't apply. Note also that
(currently) all systemd callers of laccess() pass mode as F_OK, so
only check for existence of a file, not access permissions.
Therefore, in this case, the only distiction between faccessat()
with (flag == 0) and (flag == AT_SYMLINK_NOFOLLOW) is the behaviour
for broken symlinks; laccess() on a broken symlink will succeed with
(flag == AT_SYMLINK_NOFOLLOW) and fail (flag == 0).
The laccess() macros was added to systemd some time ago and it's not
clear if or why it needs to return success for broken symlinks. Maybe
just historical and not actually necessary or desired behaviour?
Signed-off-by: Andre McCurdy <armccurdy@gmail.com>
---
Upstream-Status: Pending
src/basic/fs-util.h | 22 +++++++++++++++++++++-
src/shared/base-filesystem.c | 6 +++---
2 files changed, 24 insertions(+), 4 deletions(-)
diff --git a/src/basic/fs-util.h b/src/basic/fs-util.h
index 094acf179..cdbc0ae72 100644
--- a/src/basic/fs-util.h
+++ b/src/basic/fs-util.h
@@ -48,7 +48,27 @@ int fchmod_umask(int fd, mode_t mode);
int fd_warn_permissions(const char *path, int fd);
-#define laccess(path, mode) faccessat(AT_FDCWD, (path), (mode), AT_SYMLINK_NOFOLLOW)
+/*
+ Avoid using AT_SYMLINK_NOFOLLOW flag. It doesn't seem like the right thing to
+ do and it's not portable (not supported by musl). See:
+
+ http://lists.landley.net/pipermail/toybox-landley.net/2014-September/003610.html
+ http://www.openwall.com/lists/musl/2015/02/05/2
+
+ Note that laccess() is never passing AT_EACCESS so a lot of the discussion in
+ the links above doesn't apply. Note also that (currently) all systemd callers
+ of laccess() pass mode as F_OK, so only check for existence of a file, not
+ access permissions. Therefore, in this case, the only distiction between
+ faccessat() with (flag == 0) and (flag == AT_SYMLINK_NOFOLLOW) is the
+ behaviour for broken symlinks; laccess() on a broken symlink will succeed
+ with (flag == AT_SYMLINK_NOFOLLOW) and fail (flag == 0).
+
+ The laccess() macros was added to systemd some time ago and it's not clear if
+ or why it needs to return success for broken symlinks. Maybe just historical
+ and not actually necessary or desired behaviour?
+*/
+
+#define laccess(path, mode) faccessat(AT_FDCWD, (path), (mode), 0)
int touch_file(const char *path, bool parents, usec_t stamp, uid_t uid, gid_t gid, mode_t mode);
int touch(const char *path);
diff --git a/src/shared/base-filesystem.c b/src/shared/base-filesystem.c
index 903a18786..2f6052ee7 100644
--- a/src/shared/base-filesystem.c
+++ b/src/shared/base-filesystem.c
@@ -70,7 +70,7 @@ int base_filesystem_create(const char *root, uid_t uid, gid_t gid) {
return log_error_errno(errno, "Failed to open root file system: %m");
for (i = 0; i < ELEMENTSOF(table); i ++) {
- if (faccessat(fd, table[i].dir, F_OK, AT_SYMLINK_NOFOLLOW) >= 0)
+ if (faccessat(fd, table[i].dir, F_OK, 0) >= 0)
continue;
if (table[i].target) {
@@ -78,7 +78,7 @@ int base_filesystem_create(const char *root, uid_t uid, gid_t gid) {
/* check if one of the targets exists */
NULSTR_FOREACH(s, table[i].target) {
- if (faccessat(fd, s, F_OK, AT_SYMLINK_NOFOLLOW) < 0)
+ if (faccessat(fd, s, F_OK, 0) < 0)
continue;
/* check if a specific file exists at the target path */
@@ -89,7 +89,7 @@ int base_filesystem_create(const char *root, uid_t uid, gid_t gid) {
if (!p)
return log_oom();
- if (faccessat(fd, p, F_OK, AT_SYMLINK_NOFOLLOW) < 0)
+ if (faccessat(fd, p, F_OK, 0) < 0)
continue;
}
--
2.14.2
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