Re: How is pivot_root intended to be used?
Thank you, I think I will change the code to be like:
int old_root = open("/", O_DIRECTORY);
if (-1 == old_root) {
perror("open");
return EXIT_FAILURE;
}
if (-1 == syscall(__NR_pivot_root, ".", ".")) {
perror("pivot_root");
return EXIT_FAILURE;
}
if (-1 == fchdir(old_root)) {
perror("fchdir");
return EXIT_FAILURE;
}
if (-1 == umount2(".", MNT_DETACH)) {
perror("umount");
return EXIT_FAILURE;
}
if (-1 == close(old_root)) {
perror("close");
return EXIT_FAILURE;
}
if (-1 == chdir("/")) {
perror("chdir");
return EXIT_FAILURE;
}
This seems more understandable to me and less likely to have bugs later on.
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Re: How is pivot_root intended to be used?
Thank you, I think I will change the code to be like:
int old_root = open(/, O_DIRECTORY);
if (-1 == old_root) {
perror(open);
return EXIT_FAILURE;
}
if (-1 == syscall(__NR_pivot_root, ., .)) {
perror(pivot_root);
return EXIT_FAILURE;
}
if (-1 == fchdir(old_root)) {
perror(fchdir);
return EXIT_FAILURE;
}
if (-1 == umount2(., MNT_DETACH)) {
perror(umount);
return EXIT_FAILURE;
}
if (-1 == close(old_root)) {
perror(close);
return EXIT_FAILURE;
}
if (-1 == chdir(/)) {
perror(chdir);
return EXIT_FAILURE;
}
This seems more understandable to me and less likely to have bugs later on.
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Re: How is pivot_root intended to be used?
On 09/01/2014 02:19 PM, Steven Stewart-Gallus wrote:
Hello,
I am not confused about how I can currently use pivot_root for
containers on my kernel (version 3.13). Currently a sequence like:
if (-1 == syscall(__NR_pivot_root, ".", ".")) {
perror("pivot_root");
return EXIT_FAILURE;
}
if (-1 == umount2(".", MNT_DETACH)) {
perror("umount");
return EXIT_FAILURE;
Given the comment, you don't know what '.' refers to in the umount2 call
above. In fact, I think you're actually detaching the wrong thing,
leaving possible security issues.
See:
https://github.com/sandstorm-io/sandstorm/blob/master/src/sandstorm/supervisor-main.c%2B%2B#L922
for a program that does this more carefully.
--Andy
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Re: How is pivot_root intended to be used?
On 09/01/2014 02:19 PM, Steven Stewart-Gallus wrote:
Hello,
I am not confused about how I can currently use pivot_root for
containers on my kernel (version 3.13). Currently a sequence like:
if (-1 == syscall(__NR_pivot_root, ., .)) {
perror(pivot_root);
return EXIT_FAILURE;
}
if (-1 == umount2(., MNT_DETACH)) {
perror(umount);
return EXIT_FAILURE;
Given the comment, you don't know what '.' refers to in the umount2 call
above. In fact, I think you're actually detaching the wrong thing,
leaving possible security issues.
See:
https://github.com/sandstorm-io/sandstorm/blob/master/src/sandstorm/supervisor-main.c%2B%2B#L922
for a program that does this more carefully.
--Andy
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How is pivot_root intended to be used?
Hello,
I am not confused about how I can currently use pivot_root for
containers on my kernel (version 3.13). Currently a sequence like:
if (-1 == syscall(__NR_pivot_root, ".", ".")) {
perror("pivot_root");
return EXIT_FAILURE;
}
if (-1 == umount2(".", MNT_DETACH)) {
perror("umount");
return EXIT_FAILURE;
}
/* pivot_root() may or may not affect its current working
* directory. It is therefore recommended to call chdir("/")
* immediately after pivot_root().
*
* - http://man7.org/linux/man-pages/man2/pivot_root.2.html
*/
if (-1 == chdir("/")) {
perror("chdir");
return EXIT_FAILURE;
}
works. However, I am completely and totally confused about how the
pivot_root system call is intended to be used here and have absolutely
no idea if this will work in the future. This concerns me because I
don't want my program to potentially develop silent security bugs on
future versions of the Linux kernel.
Some information about the context. I am sandboxing a program just
after it has done a fork, unshared the mount namespace, setup a
sandbox directory and changed into it. If you just want to look at the
code, the actual code is avaliable at
https://gitorious.org/linted/linted/source/b25685ba4762bfb794c8f36ae74276d32d2b0ca8:src/spawn/spawn.c.
Thank you,
Steven Stewart-Gallus
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How is pivot_root intended to be used?
Hello,
I am not confused about how I can currently use pivot_root for
containers on my kernel (version 3.13). Currently a sequence like:
if (-1 == syscall(__NR_pivot_root, ., .)) {
perror(pivot_root);
return EXIT_FAILURE;
}
if (-1 == umount2(., MNT_DETACH)) {
perror(umount);
return EXIT_FAILURE;
}
/* pivot_root() may or may not affect its current working
* directory. It is therefore recommended to call chdir(/)
* immediately after pivot_root().
*
* - http://man7.org/linux/man-pages/man2/pivot_root.2.html
*/
if (-1 == chdir(/)) {
perror(chdir);
return EXIT_FAILURE;
}
works. However, I am completely and totally confused about how the
pivot_root system call is intended to be used here and have absolutely
no idea if this will work in the future. This concerns me because I
don't want my program to potentially develop silent security bugs on
future versions of the Linux kernel.
Some information about the context. I am sandboxing a program just
after it has done a fork, unshared the mount namespace, setup a
sandbox directory and changed into it. If you just want to look at the
code, the actual code is avaliable at
https://gitorious.org/linted/linted/source/b25685ba4762bfb794c8f36ae74276d32d2b0ca8:src/spawn/spawn.c.
Thank you,
Steven Stewart-Gallus
--
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