setuid/setgid mode bits not always retained
srd424 opened this issue · 2 comments
Setuid/setgid bits are not always retained on extract. I notice this most obviously when moving Ubuntu containers around, in /sbin pam_extrausers_chkpwd and unix_chkpwd should be setgid. They get created correctly, but then reset:
15841 openat(7, ".#unix_chkpwdf53ffc41b6fa1c73", O_WRONLY|O_CREAT|O_EXCL|O_NOCTTY|O_NOFOLLOW|O_CLOEXEC, 0102755) = 8
15841 ioctl(8, FS_IOC_GETFLAGS, 0x7fff18156ca4) = 0
15841 write(8, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0(\0\1\0\0\0Y\26\0\0004\0\0\0"..., 21928) = 21928
15841 fstat(8, {st_mode=S_IFREG|S_ISGID|0755, st_size=21928, ...}) = 0
15841 fchown(8, 0, 42) = 0
15841 fgetxattr(8, "security.capability", 0x7fff18156b68, 1) = -1 ENODATA (No data available)
15841 fgetxattr(8, "security.selinux", 0x55f3b4f42920, 255) = -1 ENODATA (No data available)
15841 utimensat(8, NULL, [UTIME_OMIT, {tv_sec=1551277610, tv_nsec=0} /* 2019-02-27T14:26:50+0000 */], 0) = 0
15841 renameat(7, ".#unix_chkpwdf53ffc41b6fa1c73", 7, "unix_chkpwd") = 0
15841 ioctl(8, FS_IOC_GETFLAGS, 0x7fff18156ad4) = 0
15841 fstat(8, {st_mode=S_IFREG|0755, st_size=21928, ...}) = 0
15841 close(8) = 0
fchown(2) behaviour on Linux seems to be responsible, per man page:
When the owner or group of an executable file is changed by an unprivileged user, the S_ISUID and S_ISGID mode bits are cleared. POSIX does not specify whether this also should happen when root does the chown(); the Linux behavior depends on the kernel version, and since Linux 2.2.13, root is treated like other users.
ca_decoder_finalize_child performs the fchown(), so probably needs to reset the mode again afterwards...
Slightly baffled how this one has slipped through the net for so long?
Attached should do the trick (sorry, I'm a dinosaur who doesn't do git..)
OK, I think I've managed to do a PR. I feel a bit like a T. Rex trying to fly an A380..