Commit bfb819ea20ce ("proc: Check /proc/$pid/attr/ writes against file opener")
tried to make sure that there could not be a confusion between the opener of
a /proc/$pid/attr/ file and the writer. It used struct cred to make sure
the privileges didn't change. However, there were existing cases where a more
privileged thread was passing the opened fd to a differently privileged thread
(during container setup). Instead, use mm_struct to track whether the opener
and writer are still the same process. (This is what several other proc files
already do, though for different reasons.)
Reported-by: Christian Brauner <[email protected]>
Reported-by: Andrea Righi <[email protected]>
Tested-by: Andrea Righi <[email protected]>
Fixes: bfb819ea20ce ("proc: Check /proc/$pid/attr/ writes against file opener")
Cc: [email protected]
Signed-off-by: Kees Cook <[email protected]>
---
fs/proc/base.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/fs/proc/base.c b/fs/proc/base.c
index 58bbf334265b..7118ebe38fa6 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2674,6 +2674,11 @@ static int proc_pident_readdir(struct file *file, struct dir_context *ctx,
}
#ifdef CONFIG_SECURITY
+static int proc_pid_attr_open(struct inode *inode, struct file *file)
+{
+ return __mem_open(inode, file, PTRACE_MODE_READ_FSCREDS);
+}
+
static ssize_t proc_pid_attr_read(struct file * file, char __user * buf,
size_t count, loff_t *ppos)
{
@@ -2704,7 +2709,7 @@ static ssize_t proc_pid_attr_write(struct file * file, const char __user * buf,
int rv;
/* A task may only write when it was the opener. */
- if (file->f_cred != current_real_cred())
+ if (file->private_data != current->mm)
return -EPERM;
rcu_read_lock();
@@ -2754,9 +2759,11 @@ static ssize_t proc_pid_attr_write(struct file * file, const char __user * buf,
}
static const struct file_operations proc_pid_attr_operations = {
+ .open = proc_pid_attr_open,
.read = proc_pid_attr_read,
.write = proc_pid_attr_write,
.llseek = generic_file_llseek,
+ .release = mem_release,
};
#define LSM_DIR_OPS(LSM) \
--
2.25.1
On Tue, Jun 08, 2021 at 10:12:21AM -0700, Kees Cook wrote:
> Commit bfb819ea20ce ("proc: Check /proc/$pid/attr/ writes against file opener")
> tried to make sure that there could not be a confusion between the opener of
> a /proc/$pid/attr/ file and the writer. It used struct cred to make sure
> the privileges didn't change. However, there were existing cases where a more
> privileged thread was passing the opened fd to a differently privileged thread
> (during container setup). Instead, use mm_struct to track whether the opener
> and writer are still the same process. (This is what several other proc files
> already do, though for different reasons.)
>
> Reported-by: Christian Brauner <[email protected]>
> Reported-by: Andrea Righi <[email protected]>
> Tested-by: Andrea Righi <[email protected]>
> Fixes: bfb819ea20ce ("proc: Check /proc/$pid/attr/ writes against file opener")
> Cc: [email protected]
> Signed-off-by: Kees Cook <[email protected]>
> ---
Thanks!
Acked-by: Christian Brauner <[email protected]>
I used mainline kernel on android, this patch cause "failed to retrieve pid context" problem.
06-14 02:15:51.165 1685 1685 E ServiceManager: SELinux: getpidcon(pid=1682) failed to retrieve pid context.
06-14 02:15:51.166 1685 1685 E ServiceManager: add_service('batteryproperties',1) uid=0 - PERMISSION DENIED
06-14 02:15:51.166 1682 1682 I ServiceManager: addService() batteryproperties failed (err -1 - no service manager yet?). Retrying...
06-14 02:15:51.197 1685 1685 E ServiceManager: SELinux: getpidcon(pid=1695) failed to retrieve pid context.
06-14 02:15:51.197 1685 1685 E ServiceManager: add_service('android.security.keystore',1) uid=1017 - PERMISSION DENIED
06-14 02:15:51.198 1695 1695 I ServiceManager: addService() android.security.keystore failed (err -1 - no service manager yet?). Retrying...
06-14 02:15:51.207 1685 1685 E ServiceManager: SELinux: getpidcon(pid=1708) failed to retrieve pid context.
06-14 02:15:51.207 1685 1685 E ServiceManager: add_service('android.service.gatekeeper.IGateKeeperService',1) uid=1000 - PERMISSION DENIED
06-14 02:15:51.207 1708 1708 I ServiceManager: addService() android.service.gatekeeper.IGateKeeperService failed (err -1 - no service manager yet?). Retrying...
06-14 02:15:51.275 1685 1685 E ServiceManager: SELinux: getpidcon(pid=1693) failed to retrieve pid context.
06-14 02:15:51.275 1692 1692 I cameraserver: ServiceManager: 0xf6d309e0
06-14 02:15:51.275 1685 1685 E ServiceManager: add_service('drm.drmManager',1) uid=1019 - PERMISSION DENIED
06-14 02:15:51.276 1693 1693 I ServiceManager: addService() drm.drmManager failed (err -1 - no service manager yet?). Retrying...
On Mon, Jun 14, 2021 at 06:02:34PM +0800, youling257 wrote:
> I used mainline kernel on android, this patch cause "failed to retrieve pid context" problem.
>
> 06-14 02:15:51.165 1685 1685 E ServiceManager: SELinux: getpidcon(pid=1682) failed to retrieve pid context.
> 06-14 02:15:51.166 1685 1685 E ServiceManager: add_service('batteryproperties',1) uid=0 - PERMISSION DENIED
> 06-14 02:15:51.166 1682 1682 I ServiceManager: addService() batteryproperties failed (err -1 - no service manager yet?). Retrying...
> 06-14 02:15:51.197 1685 1685 E ServiceManager: SELinux: getpidcon(pid=1695) failed to retrieve pid context.
> 06-14 02:15:51.197 1685 1685 E ServiceManager: add_service('android.security.keystore',1) uid=1017 - PERMISSION DENIED
> 06-14 02:15:51.198 1695 1695 I ServiceManager: addService() android.security.keystore failed (err -1 - no service manager yet?). Retrying...
> 06-14 02:15:51.207 1685 1685 E ServiceManager: SELinux: getpidcon(pid=1708) failed to retrieve pid context.
> 06-14 02:15:51.207 1685 1685 E ServiceManager: add_service('android.service.gatekeeper.IGateKeeperService',1) uid=1000 - PERMISSION DENIED
> 06-14 02:15:51.207 1708 1708 I ServiceManager: addService() android.service.gatekeeper.IGateKeeperService failed (err -1 - no service manager yet?). Retrying...
> 06-14 02:15:51.275 1685 1685 E ServiceManager: SELinux: getpidcon(pid=1693) failed to retrieve pid context.
> 06-14 02:15:51.275 1692 1692 I cameraserver: ServiceManager: 0xf6d309e0
> 06-14 02:15:51.275 1685 1685 E ServiceManager: add_service('drm.drmManager',1) uid=1019 - PERMISSION DENIED
> 06-14 02:15:51.276 1693 1693 I ServiceManager: addService() drm.drmManager failed (err -1 - no service manager yet?). Retrying...
>
Argh. Are you able to uncover what userspace is doing here?
So far, my test cases are:
1) self: open, write, close: allowed
2) self: open, clone thread. thread: change privileges, write, close: allowed
3) self: open, give to privileged process. privileged process: write: reject
--
Kees Cook
On Mon, Jun 14, 2021 at 08:32:35AM -0700, Kees Cook wrote:
> On Mon, Jun 14, 2021 at 06:02:34PM +0800, youling257 wrote:
> > I used mainline kernel on android, this patch cause "failed to retrieve pid context" problem.
> >
> > 06-14 02:15:51.165 1685 1685 E ServiceManager: SELinux: getpidcon(pid=1682) failed to retrieve pid context.
I found getpidcon() in libselinux:
https://github.com/SELinuxProject/selinux/blob/master/libselinux/src/procattr.c#L159
> > 06-14 02:15:51.166 1685 1685 E ServiceManager: add_service('batteryproperties',1) uid=0 - PERMISSION DENIED
> > 06-14 02:15:51.166 1682 1682 I ServiceManager: addService() batteryproperties failed (err -1 - no service manager yet?). Retrying...
> > 06-14 02:15:51.197 1685 1685 E ServiceManager: SELinux: getpidcon(pid=1695) failed to retrieve pid context.
> > 06-14 02:15:51.197 1685 1685 E ServiceManager: add_service('android.security.keystore',1) uid=1017 - PERMISSION DENIED
> > 06-14 02:15:51.198 1695 1695 I ServiceManager: addService() android.security.keystore failed (err -1 - no service manager yet?). Retrying...
> > 06-14 02:15:51.207 1685 1685 E ServiceManager: SELinux: getpidcon(pid=1708) failed to retrieve pid context.
> > 06-14 02:15:51.207 1685 1685 E ServiceManager: add_service('android.service.gatekeeper.IGateKeeperService',1) uid=1000 - PERMISSION DENIED
> > 06-14 02:15:51.207 1708 1708 I ServiceManager: addService() android.service.gatekeeper.IGateKeeperService failed (err -1 - no service manager yet?). Retrying...
> > 06-14 02:15:51.275 1685 1685 E ServiceManager: SELinux: getpidcon(pid=1693) failed to retrieve pid context.
> > 06-14 02:15:51.275 1692 1692 I cameraserver: ServiceManager: 0xf6d309e0
> > 06-14 02:15:51.275 1685 1685 E ServiceManager: add_service('drm.drmManager',1) uid=1019 - PERMISSION DENIED
> > 06-14 02:15:51.276 1693 1693 I ServiceManager: addService() drm.drmManager failed (err -1 - no service manager yet?). Retrying...
> >
>
> Argh. Are you able to uncover what userspace is doing here?
It looks like this is a case of attempting to _read_ the attr file, and
the new opener check was requiring the opener/target relationship pass
the mm_access() checks, which is clearly too strict.
> So far, my test cases are:
>
> 1) self: open, write, close: allowed
> 2) self: open, clone thread. thread: change privileges, write, close: allowed
> 3) self: open, give to privileged process. privileged process: write: reject
I've now added:
4) self: open privileged process's attr, read, close: allowed
Can folks please test this patch to double-check?
diff --git a/fs/proc/base.c b/fs/proc/base.c
index 7118ebe38fa6..7c55301674e0 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2676,7 +2676,14 @@ static int proc_pident_readdir(struct file *file, struct dir_context *ctx,
#ifdef CONFIG_SECURITY
static int proc_pid_attr_open(struct inode *inode, struct file *file)
{
- return __mem_open(inode, file, PTRACE_MODE_READ_FSCREDS);
+ struct mm_struct *mm = __mem_open(inode, file, PTRACE_MODE_READ_FSCREDS);
+
+ /* Reads do not require mm_struct access. */
+ if (IS_ERR(mm))
+ mm = NULL;
+
+ file->private_data = mm;
+ return 0;
}
static ssize_t proc_pid_attr_read(struct file * file, char __user * buf,
@@ -2709,7 +2716,7 @@ static ssize_t proc_pid_attr_write(struct file * file, const char __user * buf,
int rv;
/* A task may only write when it was the opener. */
- if (file->private_data != current->mm)
+ if (!file->private_data || file->private_data != current->mm)
return -EPERM;
rcu_read_lock();
Wheee.
--
Kees Cook
On 6/14/2021 8:32 AM, Kees Cook wrote:
> On Mon, Jun 14, 2021 at 06:02:34PM +0800, youling257 wrote:
>> I used mainline kernel on android, this patch cause "failed to retrieve pid context" problem.
>>
>> 06-14 02:15:51.165 1685 1685 E ServiceManager: SELinux: getpidcon(pid=1682) failed to retrieve pid context.
>> 06-14 02:15:51.166 1685 1685 E ServiceManager: add_service('batteryproperties',1) uid=0 - PERMISSION DENIED
>> 06-14 02:15:51.166 1682 1682 I ServiceManager: addService() batteryproperties failed (err -1 - no service manager yet?). Retrying...
>> 06-14 02:15:51.197 1685 1685 E ServiceManager: SELinux: getpidcon(pid=1695) failed to retrieve pid context.
>> 06-14 02:15:51.197 1685 1685 E ServiceManager: add_service('android.security.keystore',1) uid=1017 - PERMISSION DENIED
>> 06-14 02:15:51.198 1695 1695 I ServiceManager: addService() android.security.keystore failed (err -1 - no service manager yet?). Retrying...
>> 06-14 02:15:51.207 1685 1685 E ServiceManager: SELinux: getpidcon(pid=1708) failed to retrieve pid context.
>> 06-14 02:15:51.207 1685 1685 E ServiceManager: add_service('android.service.gatekeeper.IGateKeeperService',1) uid=1000 - PERMISSION DENIED
>> 06-14 02:15:51.207 1708 1708 I ServiceManager: addService() android.service.gatekeeper.IGateKeeperService failed (err -1 - no service manager yet?). Retrying...
>> 06-14 02:15:51.275 1685 1685 E ServiceManager: SELinux: getpidcon(pid=1693) failed to retrieve pid context.
>> 06-14 02:15:51.275 1692 1692 I cameraserver: ServiceManager: 0xf6d309e0
>> 06-14 02:15:51.275 1685 1685 E ServiceManager: add_service('drm.drmManager',1) uid=1019 - PERMISSION DENIED
>> 06-14 02:15:51.276 1693 1693 I ServiceManager: addService() drm.drmManager failed (err -1 - no service manager yet?). Retrying...
>>
> Argh. Are you able to uncover what userspace is doing here?
>
> So far, my test cases are:
>
> 1) self: open, write, close: allowed
> 2) self: open, clone thread. thread: change privileges, write, close: allowed
> 3) self: open, give to privileged process. privileged process: write: reject
I found an issue under Smack where a privileged process opened
/proc/self/attr/smack/current, wrote to it successfully, then tried
to write to it again, which failed because the cred has changed.
That's not a common use case. The usual case is open, write, close.
If ServiceManager is assuming that it can leave a descriptor open
while manipulations are in progress it could encounter the same kind
of problem.
On Mon, Jun 14, 2021 at 9:45 AM Kees Cook <[email protected]> wrote:
>
> /* A task may only write when it was the opener. */
> - if (file->private_data != current->mm)
> + if (!file->private_data || file->private_data != current->mm)
I don't think this is necessary.
If file->private_data is NULL, then the old test for private_data !=
current->mm will still work just fine.
Because if you can fool kernel threads to do the write for you, you
have bigger security issues than that test.
Linus
I test this patch cause "init: cannot setexeccon(u:r:ueventd:s0)
operation not permitted.
init ctrl_write_limited.
2021-06-15 0:45 GMT+08:00, Kees Cook <[email protected]>:
> On Mon, Jun 14, 2021 at 08:32:35AM -0700, Kees Cook wrote:
>> On Mon, Jun 14, 2021 at 06:02:34PM +0800, youling257 wrote:
>> > I used mainline kernel on android, this patch cause "failed to retrieve
>> > pid context" problem.
>> >
>> > 06-14 02:15:51.165 1685 1685 E ServiceManager: SELinux:
>> > getpidcon(pid=1682) failed to retrieve pid context.
>
> I found getpidcon() in libselinux:
> https://github.com/SELinuxProject/selinux/blob/master/libselinux/src/procattr.c#L159
>
>> > 06-14 02:15:51.166 1685 1685 E ServiceManager:
>> > add_service('batteryproperties',1) uid=0 - PERMISSION DENIED
>> > 06-14 02:15:51.166 1682 1682 I ServiceManager: addService()
>> > batteryproperties failed (err -1 - no service manager yet?).
>> > Retrying...
>> > 06-14 02:15:51.197 1685 1685 E ServiceManager: SELinux:
>> > getpidcon(pid=1695) failed to retrieve pid context.
>> > 06-14 02:15:51.197 1685 1685 E ServiceManager:
>> > add_service('android.security.keystore',1) uid=1017 - PERMISSION DENIED
>> > 06-14 02:15:51.198 1695 1695 I ServiceManager: addService()
>> > android.security.keystore failed (err -1 - no service manager yet?).
>> > Retrying...
>> > 06-14 02:15:51.207 1685 1685 E ServiceManager: SELinux:
>> > getpidcon(pid=1708) failed to retrieve pid context.
>> > 06-14 02:15:51.207 1685 1685 E ServiceManager:
>> > add_service('android.service.gatekeeper.IGateKeeperService',1) uid=1000
>> > - PERMISSION DENIED
>> > 06-14 02:15:51.207 1708 1708 I ServiceManager: addService()
>> > android.service.gatekeeper.IGateKeeperService failed (err -1 - no
>> > service manager yet?). Retrying...
>> > 06-14 02:15:51.275 1685 1685 E ServiceManager: SELinux:
>> > getpidcon(pid=1693) failed to retrieve pid context.
>> > 06-14 02:15:51.275 1692 1692 I cameraserver: ServiceManager:
>> > 0xf6d309e0
>> > 06-14 02:15:51.275 1685 1685 E ServiceManager:
>> > add_service('drm.drmManager',1) uid=1019 - PERMISSION DENIED
>> > 06-14 02:15:51.276 1693 1693 I ServiceManager: addService()
>> > drm.drmManager failed (err -1 - no service manager yet?). Retrying...
>> >
>>
>> Argh. Are you able to uncover what userspace is doing here?
>
> It looks like this is a case of attempting to _read_ the attr file, and
> the new opener check was requiring the opener/target relationship pass
> the mm_access() checks, which is clearly too strict.
>
>> So far, my test cases are:
>>
>> 1) self: open, write, close: allowed
>> 2) self: open, clone thread. thread: change privileges, write, close:
>> allowed
>> 3) self: open, give to privileged process. privileged process: write:
>> reject
>
> I've now added:
>
> 4) self: open privileged process's attr, read, close: allowed
>
> Can folks please test this patch to double-check?
>
>
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index 7118ebe38fa6..7c55301674e0 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -2676,7 +2676,14 @@ static int proc_pident_readdir(struct file *file,
> struct dir_context *ctx,
> #ifdef CONFIG_SECURITY
> static int proc_pid_attr_open(struct inode *inode, struct file *file)
> {
> - return __mem_open(inode, file, PTRACE_MODE_READ_FSCREDS);
> + struct mm_struct *mm = __mem_open(inode, file, PTRACE_MODE_READ_FSCREDS);
> +
> + /* Reads do not require mm_struct access. */
> + if (IS_ERR(mm))
> + mm = NULL;
> +
> + file->private_data = mm;
> + return 0;
> }
>
> static ssize_t proc_pid_attr_read(struct file * file, char __user * buf,
> @@ -2709,7 +2716,7 @@ static ssize_t proc_pid_attr_write(struct file * file,
> const char __user * buf,
> int rv;
>
> /* A task may only write when it was the opener. */
> - if (file->private_data != current->mm)
> + if (!file->private_data || file->private_data != current->mm)
> return -EPERM;
>
> rcu_read_lock();
>
>
> Wheee.
>
> --
> Kees Cook
>
On Tue, Jun 15, 2021 at 02:46:19AM +0800, youling 257 wrote:
> I test this patch cause "init: cannot setexeccon(u:r:ueventd:s0)
> operation not permitted.
> init ctrl_write_limited.
Thanks for testing!
This appears to come from here:
https://github.com/aosp-mirror/platform_system_core/blob/master/init/service.cpp#L242
In setexeccon(), I see (pid=0, attr="exec"):
fd = openattr(pid, attr, O_RDWR | O_CLOEXEC);
...
ret = write(fd, context2, strlen(context2) + 1);
...
close(fd);
and openattr() is doing:
...
rc = asprintf(&path, "/proc/thread-self/attr/%s", attr);
if (rc < 0)
return -1;
fd = open(path, flags | O_CLOEXEC);
...
I'm not sure how the above could fail. (mm_access() always allows
introspection...)
The only way I can understand the check failing is if a process did:
open, exec, write
But setexeccon() is not doing anything between the open and the write...
I will keep looking...
-Kees
--
Kees Cook
if try to find problem on userspace, i used linux 5.13rc6 on old
android 7 cm14.1, not aosp android 11.
http://git.osdn.net/view?p=android-x86/system-core.git;a=blob;f=init/service.cpp;h=a5334f447fc2fc34453d2f6a37523bedccadc690;hb=refs/heads/cm-14.1-x86#l457
457 if (!seclabel_.empty()) {
458 if (setexeccon(seclabel_.c_str()) < 0) {
459 ERROR("cannot setexeccon('%s'): %s\n",
460 seclabel_.c_str(), strerror(errno));
461 _exit(127);
462 }
463 }
2021-06-15 6:50 GMT+08:00, Kees Cook <[email protected]>:
> On Tue, Jun 15, 2021 at 02:46:19AM +0800, youling 257 wrote:
>> I test this patch cause "init: cannot setexeccon(u:r:ueventd:s0)
>> operation not permitted.
>> init ctrl_write_limited.
>
> Thanks for testing!
>
> This appears to come from here:
> https://github.com/aosp-mirror/platform_system_core/blob/master/init/service.cpp#L242
>
>
> In setexeccon(), I see (pid=0, attr="exec"):
>
> fd = openattr(pid, attr, O_RDWR | O_CLOEXEC);
> ...
> ret = write(fd, context2, strlen(context2) + 1);
> ...
> close(fd);
>
>
> and openattr() is doing:
> ...
> rc = asprintf(&path, "/proc/thread-self/attr/%s", attr);
> if (rc < 0)
> return -1;
> fd = open(path, flags | O_CLOEXEC);
> ...
>
> I'm not sure how the above could fail. (mm_access() always allows
> introspection...)
>
> The only way I can understand the check failing is if a process did:
>
> open, exec, write
>
> But setexeccon() is not doing anything between the open and the write...
>
> I will keep looking...
>
> -Kees
>
> --
> Kees Cook
>
On Mon, Jun 14, 2021 at 6:55 PM youling 257 <[email protected]> wrote:
>
> if try to find problem on userspace, i used linux 5.13rc6 on old
> android 7 cm14.1, not aosp android 11.
> http://git.osdn.net/view?p=android-x86/system-core.git;a=blob;f=init/service.cpp;h=a5334f447fc2fc34453d2f6a37523bedccadc690;hb=refs/heads/cm-14.1-x86#l457
>
> 457 if (!seclabel_.empty()) {
> 458 if (setexeccon(seclabel_.c_str()) < 0) {
> 459 ERROR("cannot setexeccon('%s'): %s\n",
> 460 seclabel_.c_str(), strerror(errno));
> 461 _exit(127);
> 462 }
> 463 }
I have no idea where the cm14.1 libraries are. Does anybody know where
the matching source code for setexeccon() would be?
For me - obviously not on cm14.1 - all "setexeccon()" does is
n = openat(AT_FDCWD, "/proc/thread-self/attr/exec", O_RDWR|O_CLOEXEC)
write(n, string, len)
close(n)
and if that fails, it would seem to indicate that proc_mem_open()
failed. Which would be mm_access() failing. But I don't see how that
can be the case, because mm_access() explicitly allows "mm ==
current->mm" (which the above clearly should be).
youling, can you double-check with the current -git tree? But as far
as I can tell, my minimal patch is exactly the same as Kees' patch
(just smaller and simpler).
Kees, do you see anything?
Linus
On Tue, Jun 15, 2021 at 11:19:04AM -0700, Linus Torvalds wrote:
> On Mon, Jun 14, 2021 at 6:55 PM youling 257 <[email protected]> wrote:
> >
> > if try to find problem on userspace, i used linux 5.13rc6 on old
> > android 7 cm14.1, not aosp android 11.
> > http://git.osdn.net/view?p=android-x86/system-core.git;a=blob;f=init/service.cpp;h=a5334f447fc2fc34453d2f6a37523bedccadc690;hb=refs/heads/cm-14.1-x86#l457
> >
> > 457 if (!seclabel_.empty()) {
> > 458 if (setexeccon(seclabel_.c_str()) < 0) {
> > 459 ERROR("cannot setexeccon('%s'): %s\n",
> > 460 seclabel_.c_str(), strerror(errno));
> > 461 _exit(127);
> > 462 }
> > 463 }
>
> I have no idea where the cm14.1 libraries are. Does anybody know where
> the matching source code for setexeccon() would be?
>
> For me - obviously not on cm14.1 - all "setexeccon()" does is
>
> n = openat(AT_FDCWD, "/proc/thread-self/attr/exec", O_RDWR|O_CLOEXEC)
> write(n, string, len)
> close(n)
>
> and if that fails, it would seem to indicate that proc_mem_open()
> failed. Which would be mm_access() failing. But I don't see how that
> can be the case, because mm_access() explicitly allows "mm ==
> current->mm" (which the above clearly should be).
Yeah, that was what I saw too.
> youling, can you double-check with the current -git tree? But as far
> as I can tell, my minimal patch is exactly the same as Kees' patch
> (just smaller and simpler).
FWIW, for that patch:
Acked-by: Kees Cook <[email protected]>
Cc: [email protected]
>
> Kees, do you see anything?
No, I haven't been able to reproduce the failure. :(
--
Kees Cook
I test "proc: only require mm_struct for writing" fixed my cm14.1 problem.
2021-06-16 2:19 GMT+08:00, Linus Torvalds <[email protected]>:
> On Mon, Jun 14, 2021 at 6:55 PM youling 257 <[email protected]> wrote:
>>
>> if try to find problem on userspace, i used linux 5.13rc6 on old
>> android 7 cm14.1, not aosp android 11.
>> http://git.osdn.net/view?p=android-x86/system-core.git;a=blob;f=init/service.cpp;h=a5334f447fc2fc34453d2f6a37523bedccadc690;hb=refs/heads/cm-14.1-x86#l457
>>
>> 457 if (!seclabel_.empty()) {
>> 458 if (setexeccon(seclabel_.c_str()) < 0) {
>> 459 ERROR("cannot setexeccon('%s'): %s\n",
>> 460 seclabel_.c_str(), strerror(errno));
>> 461 _exit(127);
>> 462 }
>> 463 }
>
> I have no idea where the cm14.1 libraries are. Does anybody know where
> the matching source code for setexeccon() would be?
>
> For me - obviously not on cm14.1 - all "setexeccon()" does is
>
> n = openat(AT_FDCWD, "/proc/thread-self/attr/exec", O_RDWR|O_CLOEXEC)
> write(n, string, len)
> close(n)
>
> and if that fails, it would seem to indicate that proc_mem_open()
> failed. Which would be mm_access() failing. But I don't see how that
> can be the case, because mm_access() explicitly allows "mm ==
> current->mm" (which the above clearly should be).
>
> youling, can you double-check with the current -git tree? But as far
> as I can tell, my minimal patch is exactly the same as Kees' patch
> (just smaller and simpler).
>
> Kees, do you see anything?
>
> Linus
>
On Tue, Jun 15, 2021 at 02:50:39PM -0700, Kees Cook wrote:
> On Tue, Jun 15, 2021 at 11:19:04AM -0700, Linus Torvalds wrote:
> > On Mon, Jun 14, 2021 at 6:55 PM youling 257 <[email protected]> wrote:
> > >
> > > if try to find problem on userspace, i used linux 5.13rc6 on old
> > > android 7 cm14.1, not aosp android 11.
> > > http://git.osdn.net/view?p=android-x86/system-core.git;a=blob;f=init/service.cpp;h=a5334f447fc2fc34453d2f6a37523bedccadc690;hb=refs/heads/cm-14.1-x86#l457
> > >
> > > 457 if (!seclabel_.empty()) {
> > > 458 if (setexeccon(seclabel_.c_str()) < 0) {
> > > 459 ERROR("cannot setexeccon('%s'): %s\n",
> > > 460 seclabel_.c_str(), strerror(errno));
> > > 461 _exit(127);
> > > 462 }
> > > 463 }
> >
> > I have no idea where the cm14.1 libraries are. Does anybody know where
> > the matching source code for setexeccon() would be?
> >
> > For me - obviously not on cm14.1 - all "setexeccon()" does is
> >
> > n = openat(AT_FDCWD, "/proc/thread-self/attr/exec", O_RDWR|O_CLOEXEC)
> > write(n, string, len)
> > close(n)
> >
> > and if that fails, it would seem to indicate that proc_mem_open()
> > failed. Which would be mm_access() failing. But I don't see how that
> > can be the case, because mm_access() explicitly allows "mm ==
> > current->mm" (which the above clearly should be).
>
> Yeah, that was what I saw too.
>
> > youling, can you double-check with the current -git tree? But as far
> > as I can tell, my minimal patch is exactly the same as Kees' patch
> > (just smaller and simpler).
>
> FWIW, for that patch:
>
> Acked-by: Kees Cook <[email protected]>
> Cc: [email protected]
Thanks, I'll go pick it up now.
greg k-h