| Message ID | 20210608171221.276899-1-keescook@chromium.org |
|---|---|
| State | Accepted |
| Commit | 591a22c14d3f45cc38bd1931c593c221df2f1881 |
| Headers | show |
| Series | proc: Track /proc/$pid/attr/ opener mm_struct | expand |
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 <keescook@chromium.org> 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 <keescook@chromium.org>: > 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 <keescook@chromium.org>:
> 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 <youling257@gmail.com> 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 <youling257@gmail.com> 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 <keescook@chromium.org> Cc: stable@vger.kernel.org > > 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 <torvalds@linux-foundation.org>: > On Mon, Jun 14, 2021 at 6:55 PM youling 257 <youling257@gmail.com> 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 <youling257@gmail.com> 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 <keescook@chromium.org> > Cc: stable@vger.kernel.org Thanks, I'll go pick it up now. greg k-h
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) \
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/$pid/attr/ file and the writer. It used struct cred to make sure the privileges didn't change. However, there were existing cases where a more privileged thread was passing the opened fd to a differently privileged thread (during container setup). Instead, use mm_struct to track whether the opener and writer are still the same process. (This is what several other proc files already do, though for different reasons.) Reported-by: Christian Brauner <christian.brauner@ubuntu.com> Reported-by: Andrea Righi <andrea.righi@canonical.com> Tested-by: Andrea Righi <andrea.righi@canonical.com> Fixes: bfb819ea20ce ("proc: Check /proc/$pid/attr/ writes against file opener") Cc: stable@vger.kernel.org Signed-off-by: Kees Cook <keescook@chromium.org> --- fs/proc/base.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-)