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use fchmod() instead of chmod() because Android 8.0 (Oreo) terminates the

process if chmod() is called
sigsegv_dump
Greg Alexander 4 years ago
parent
commit
d637261fa1
  1. 34
      NOTES
  2. 15
      rsync/syscall.c

34
NOTES

@ -431,3 +431,37 @@ anybody.
I told the most recent guy to try SuperSU. I don't have any idea if that
will really work, to be honest.
October 28, 2017.
At the beginning of October, a user notified me that rsync doesn't work
on Android 8.0 (Oreo, API 26). In the past week, Google has upgraded my
Nexus 5x to Oreo and I can confirm it.
It seems that SE Linux or something causes certain system calls to
perform the equivalent of:
fprintf(stderr, "Bad system call\n");
exit(-1);
It should return ENOSYS instead, but someone at Google is not cool enough
to be working with Unix.
The first one I discovered like this is sigprocmask(), which we can
probably do without. The next one is chmod(), which is somewhat more
useful.
The troubling thing is that I can find a file where the commandline chmod
works, but the same chmod() doesn't work in rsync.
I figured maybe my NDK was just too old ("r10d"), but I think I can't
conveniently upgrade it because Google only distributes the NDK for Linux
x86-64 now. I was using SDK 7, so I tried SDK 11, 17, 19, and got the
same result. The NDK I have also has a directory for SDK 21, but it has
typos in the header files, or they aren't compatible with its version of
gcc. But anyways, if SDK 19 doesn't work then maybe it's more than just
linking against a bad version of Bionic.
Well, I think I've got it - fchmod() works, but chmod() does not.
*shrug*

15
rsync/syscall.c

@ -214,8 +214,21 @@ int do_chmod(const char *path, mode_t mode)
# else
code = 1;
# endif
} else
} else {
#if 0
/* NB - Android 8.0 Oreo gives "Bad system call" and terminates the
* process for any call to chmod(), but fchmod() is alright */
code = chmod(path, mode & CHMOD_BITS); /* DISCOURAGED FUNCTION */
#else
int fd = open(path, O_RDONLY);
if (fd < 0) {
code = fd;
} else {
code = fchmod(fd, mode & CHMOD_BITS);
close(fd);
}
#endif
}
#endif /* !HAVE_LCHMOD */
if (code != 0 && (preserve_perms || preserve_executability))
return code;

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