On 2023-09-07 23:36, Jordi Sanfeliu wrote:
some days later, I decided to include support for lchown in the Fiwix
kernel ...<https://github.com/mikaku/Fiwix/commit/4a82a2de818436a42ab22e34caa6a68b66c93b0a>
You added lchown but removed chown? Not sure that's an improvement.
Anyway, just for fun I wrote the attached patch. Does it fix the
original problem for you? I have not installed it into Gnulib because I
lack easy access to oddball operating systems that have that particular
chown bug.
From fa893bf7902889a4375392a0f5a1f0e64e6592dc Mon Sep 17 00:00:00 2001
From: Paul Eggert <[email protected]>
Date: Fri, 8 Sep 2023 18:59:04 -0700
Subject: [PATCH] chown: work around symlink issues on odd platforms
Problem reported by Jordi Sanfeliu in:
https://lists.gnu.org/archive/html/bug-gnulib/2023-07/msg00116.html
* lib/chown.c (rpl_chown) [CHOWN_MODIFIES_SYMLINK]:
Do not declare unused locals st, stat_valid.
Redo to just call chown if arg is a symlink.
This induces a race but is perhaps the best we can do easily
on oddball platforms where chown does not follow symlinks.
---
ChangeLog | 11 ++++++++++
lib/chown.c | 63 +++++++++++++++++++++++------------------------------
2 files changed, 38 insertions(+), 36 deletions(-)
diff --git a/ChangeLog b/ChangeLog
index 2aec64130e..5963bed7d5 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,14 @@
+2023-09-08 Paul Eggert <[email protected]>
+
+ chown: work around symlink issues on odd platforms
+ Problem reported by Jordi Sanfeliu in:
+ https://lists.gnu.org/archive/html/bug-gnulib/2023-07/msg00116.html
+ * lib/chown.c (rpl_chown) [CHOWN_MODIFIES_SYMLINK]:
+ Do not declare unused locals st, stat_valid.
+ Redo to just call chown if arg is a symlink.
+ This induces a race but is perhaps the best we can do easily
+ on oddball platforms where chown does not follow symlinks.
+
2023-09-07 Paul Eggert <[email protected]>
mbscasecmp: support GNULIB_MCEL_PREFER
diff --git a/lib/chown.c b/lib/chown.c
index d735818afd..a89a460536 100644
--- a/lib/chown.c
+++ b/lib/chown.c
@@ -53,8 +53,11 @@ chown (_GL_UNUSED const char *file, _GL_UNUSED uid_t uid,
int
rpl_chown (const char *file, uid_t uid, gid_t gid)
{
+# if (CHOWN_CHANGE_TIME_BUG || CHOWN_FAILS_TO_HONOR_ID_OF_NEGATIVE_ONE \
+ || CHOWN_TRAILING_SLASH_BUG)
struct stat st;
bool stat_valid = false;
+# endif
int result;
# if CHOWN_CHANGE_TIME_BUG
@@ -80,42 +83,30 @@ rpl_chown (const char *file, uid_t uid, gid_t gid)
# endif
# if CHOWN_MODIFIES_SYMLINK
- {
- /* Handle the case in which the system-supplied chown function
- does *not* follow symlinks. Instead, it changes permissions
- on the symlink itself. To work around that, we open the
- file (but this can fail due to lack of read or write permission) and
- use fchown on the resulting descriptor. */
- int open_flags = O_NONBLOCK | O_NOCTTY | O_CLOEXEC;
- int fd = open (file, O_RDONLY | open_flags);
- if (0 <= fd
- || (errno == EACCES
- && 0 <= (fd = open (file, O_WRONLY | open_flags))))
- {
- int saved_errno;
- bool fchown_socket_failure;
-
- result = fchown (fd, uid, gid);
- saved_errno = errno;
-
- /* POSIX says fchown can fail with errno == EINVAL on sockets
- and pipes, so fall back on chown in that case. */
- fchown_socket_failure =
- (result != 0 && saved_errno == EINVAL
- && fstat (fd, &st) == 0
- && (S_ISFIFO (st.st_mode) || S_ISSOCK (st.st_mode)));
-
- close (fd);
-
- if (! fchown_socket_failure)
- {
- errno = saved_errno;
- return result;
- }
- }
- else if (errno != EACCES)
- return -1;
- }
+ /* The system-supplied chown function does not follow symlinks.
+ If the file is a symlink, open the file (following symlinks), and
+ fchown the resulting descriptor. Although the open might fail
+ due to lack of permissions, it's the best we can easily do. */
+ char linkbuf[1];
+ if (0 <= readlink (file, linkbuf, sizeof linkbuf))
+ {
+ int open_flags = O_NONBLOCK | O_NOCTTY | O_CLOEXEC;
+ int fd = open (file, O_RDONLY | open_flags);
+ if (fd < 0
+ && (errno != EACCES
+ || ((fd = open (file, O_WRONLY | open_flags)) < 0))
+ && (errno != EACCES || O_EXEC == O_RDONLY
+ || ((fd = open (file, O_EXEC | open_flags)) < 0))
+ && (errno != EACCES || O_SEARCH == O_RDONLY || O_SEARCH == O_EXEC
+ || ((fd = open (file, O_SEARCH | open_flags)) < 0)))
+ return fd;
+
+ int r = fchown (fd, uid, gid);
+ int err = errno;
+ close (fd);
+ errno = err;
+ return r;
+ }
# endif
# if CHOWN_TRAILING_SLASH_BUG
--
2.39.2
