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9 Commits
Author | SHA1 | Message | Date | |
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Christian Brauner
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f0fe2c0f05 |
binder: prevent UAF for binderfs devices II
This is a necessary follow up to the first fix I proposed and we merged in |
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Christian Brauner
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2669b8b0c7 |
binder: prevent UAF for binderfs devices
On binder_release(), binder_defer_work(proc, BINDER_DEFERRED_RELEASE) is called which punts the actual cleanup operation to a workqueue. At some point, binder_deferred_func() will be called which will end up calling binder_deferred_release() which will retrieve and cleanup the binder_context attach to this struct binder_proc. If we trace back where this binder_context is attached to binder_proc we see that it is set in binder_open() and is taken from the struct binder_device it is associated with. This obviously assumes that the struct binder_device that context is attached to is _never_ freed. While that might be true for devtmpfs binder devices it is most certainly wrong for binderfs binder devices. So, assume binder_open() is called on a binderfs binder devices. We now stash away the struct binder_context associated with that struct binder_devices: proc->context = &binder_dev->context; /* binderfs stashes devices in i_private */ if (is_binderfs_device(nodp)) { binder_dev = nodp->i_private; info = nodp->i_sb->s_fs_info; binder_binderfs_dir_entry_proc = info->proc_log_dir; } else { . . . proc->context = &binder_dev->context; Now let's assume that the binderfs instance for that binder devices is shutdown via umount() and/or the mount namespace associated with it goes away. As long as there is still an fd open for that binderfs binder device things are fine. But let's assume we now close the last fd for that binderfs binder device. Now binder_release() is called and punts to the workqueue. Assume that the workqueue has quite a bit of stuff to do and doesn't get to cleaning up the struct binder_proc and the associated struct binder_context with it for that binderfs binder device right away. In the meantime, the VFS is killing the super block and is ultimately calling sb->evict_inode() which means it will call binderfs_evict_inode() which does: static void binderfs_evict_inode(struct inode *inode) { struct binder_device *device = inode->i_private; struct binderfs_info *info = BINDERFS_I(inode); clear_inode(inode); if (!S_ISCHR(inode->i_mode) || !device) return; mutex_lock(&binderfs_minors_mutex); --info->device_count; ida_free(&binderfs_minors, device->miscdev.minor); mutex_unlock(&binderfs_minors_mutex); kfree(device->context.name); kfree(device); } thereby freeing the struct binder_device including struct binder_context. Now the workqueue finally has time to get around to cleaning up struct binder_proc and is now trying to access the associate struct binder_context. Since it's already freed it will OOPs. Fix this by holding an additional reference to the inode that is only released once the workqueue is done cleaning up struct binder_proc. This is an easy alternative to introducing separate refcounting on struct binder_device which we can always do later if it becomes necessary. This is an alternative fix to |
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Christian Brauner
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51d8a7eca6 |
binder: prevent UAF read in print_binder_transaction_log_entry()
When a binder transaction is initiated on a binder device coming from a
binderfs instance, a pointer to the name of the binder device is stashed
in the binder_transaction_log_entry's context_name member. Later on it
is used to print the name in print_binder_transaction_log_entry(). By
the time print_binder_transaction_log_entry() accesses context_name
binderfs_evict_inode() might have already freed the associated memory
thereby causing a UAF. Do the simple thing and prevent this by copying
the name of the binder device instead of stashing a pointer to it.
Reported-by: Jann Horn <jannh@google.com>
Fixes:
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Hridya Valsaraju
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4feb80faf4 |
binder: Add binder_proc logging to binderfs
Currently /sys/kernel/debug/binder/proc contains the debug data for every binder_proc instance. This patch makes this information also available in a binderfs instance mounted with a mount option "stats=global" in addition to debugfs. The patch does not affect the presence of the file in debugfs. If a binderfs instance is mounted at path /dev/binderfs, this file would be present at /dev/binderfs/binder_logs/proc. This change provides an alternate way to access this file when debugfs is not mounted. Acked-by: Christian Brauner <christian.brauner@ubuntu.com> Signed-off-by: Hridya Valsaraju <hridya@google.com> Link: https://lore.kernel.org/r/20190903161655.107408-5-hridya@google.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
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Hridya Valsaraju
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03e2e07e38 |
binder: Make transaction_log available in binderfs
Currently, the binder transaction log files 'transaction_log' and 'failed_transaction_log' live in debugfs at the following locations: /sys/kernel/debug/binder/failed_transaction_log /sys/kernel/debug/binder/transaction_log This patch makes these files also available in a binderfs instance mounted with the mount option "stats=global". It does not affect the presence of these files in debugfs. If a binderfs instance is mounted at path /dev/binderfs, the location of these files will be as follows: /dev/binderfs/binder_logs/failed_transaction_log /dev/binderfs/binder_logs/transaction_log This change provides an alternate option to access these files when debugfs is not mounted. Acked-by: Christian Brauner <christian.brauner@ubuntu.com> Signed-off-by: Hridya Valsaraju <hridya@google.com> Link: https://lore.kernel.org/r/20190903161655.107408-4-hridya@google.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
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Hridya Valsaraju
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0e13e452da |
binder: Add stats, state and transactions files
The following binder stat files currently live in debugfs. /sys/kernel/debug/binder/state /sys/kernel/debug/binder/stats /sys/kernel/debug/binder/transactions This patch makes these files available in a binderfs instance mounted with the mount option 'stats=global'. For example, if a binderfs instance is mounted at path /dev/binderfs, the above files will be available at the following locations: /dev/binderfs/binder_logs/state /dev/binderfs/binder_logs/stats /dev/binderfs/binder_logs/transactions This provides a way to access them even when debugfs is not mounted. Acked-by: Christian Brauner <christian.brauner@ubuntu.com> Signed-off-by: Hridya Valsaraju <hridya@google.com> Acked-by: Christian Brauner <christian.brauner@ubuntu.com> Link: https://lore.kernel.org/r/20190903161655.107408-3-hridya@google.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
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Hridya Valsaraju
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ca2864c6e8 |
binder: Add default binder devices through binderfs when configured
Currently, since each binderfs instance needs its own private binder devices, every time a binderfs instance is mounted, all the default binder devices need to be created via the BINDER_CTL_ADD IOCTL. This patch aims to add a solution to automatically create the default binder devices for each binderfs instance that gets mounted. To achieve this goal, when CONFIG_ANDROID_BINDERFS is set, the default binder devices specified by CONFIG_ANDROID_BINDER_DEVICES are created in each binderfs instance instead of global devices being created by the binder driver. Co-developed-by: Christian Brauner <christian.brauner@ubuntu.com> Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com> Signed-off-by: Hridya Valsaraju <hridya@google.com> Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org> Link: https://lore.kernel.org/r/20190808222727.132744-2-hridya@google.com Link: https://lore.kernel.org/r/20190904110704.8606-2-christian.brauner@ubuntu.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
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Christian Brauner
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5b9633af29 |
binderfs: remove separate device_initcall()
binderfs should not have a separate device_initcall(). When a kernel is compiled with CONFIG_ANDROID_BINDERFS register the filesystem alongside CONFIG_ANDROID_IPC. This use-case is especially sensible when users specify CONFIG_ANDROID_IPC=y, CONFIG_ANDROID_BINDERFS=y and ANDROID_BINDER_DEVICES="". When CONFIG_ANDROID_BINDERFS=n then this always succeeds so there's no regression potential for legacy workloads. Signed-off-by: Christian Brauner <christian@brauner.io> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
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Christian Brauner
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3ad20fe393 |
binder: implement binderfs
As discussed at Linux Plumbers Conference 2018 in Vancouver [1] this is the implementation of binderfs. /* Abstract */ binderfs is a backwards-compatible filesystem for Android's binder ipc mechanism. Each ipc namespace will mount a new binderfs instance. Mounting binderfs multiple times at different locations in the same ipc namespace will not cause a new super block to be allocated and hence it will be the same filesystem instance. Each new binderfs mount will have its own set of binder devices only visible in the ipc namespace it has been mounted in. All devices in a new binderfs mount will follow the scheme binder%d and numbering will always start at 0. /* Backwards compatibility */ Devices requested in the Kconfig via CONFIG_ANDROID_BINDER_DEVICES for the initial ipc namespace will work as before. They will be registered via misc_register() and appear in the devtmpfs mount. Specifically, the standard devices binder, hwbinder, and vndbinder will all appear in their standard locations in /dev. Mounting or unmounting the binderfs mount in the initial ipc namespace will have no effect on these devices, i.e. they will neither show up in the binderfs mount nor will they disappear when the binderfs mount is gone. /* binder-control */ Each new binderfs instance comes with a binder-control device. No other devices will be present at first. The binder-control device can be used to dynamically allocate binder devices. All requests operate on the binderfs mount the binder-control device resides in. Assuming a new instance of binderfs has been mounted at /dev/binderfs via mount -t binderfs binderfs /dev/binderfs. Then a request to create a new binder device can be made as illustrated in [2]. Binderfs devices can simply be removed via unlink(). /* Implementation details */ - dynamic major number allocation: When binderfs is registered as a new filesystem it will dynamically allocate a new major number. The allocated major number will be returned in struct binderfs_device when a new binder device is allocated. - global minor number tracking: Minor are tracked in a global idr struct that is capped at BINDERFS_MAX_MINOR. The minor number tracker is protected by a global mutex. This is the only point of contention between binderfs mounts. - struct binderfs_info: Each binderfs super block has its own struct binderfs_info that tracks specific details about a binderfs instance: - ipc namespace - dentry of the binder-control device - root uid and root gid of the user namespace the binderfs instance was mounted in - mountable by user namespace root: binderfs can be mounted by user namespace root in a non-initial user namespace. The devices will be owned by user namespace root. - binderfs binder devices without misc infrastructure: New binder devices associated with a binderfs mount do not use the full misc_register() infrastructure. The misc_register() infrastructure can only create new devices in the host's devtmpfs mount. binderfs does however only make devices appear under its own mountpoint and thus allocates new character device nodes from the inode of the root dentry of the super block. This will have the side-effect that binderfs specific device nodes do not appear in sysfs. This behavior is similar to devpts allocated pts devices and has no effect on the functionality of the ipc mechanism itself. [1]: https://goo.gl/JL2tfX [2]: program to allocate a new binderfs binder device: #define _GNU_SOURCE #include <errno.h> #include <fcntl.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <sys/ioctl.h> #include <sys/stat.h> #include <sys/types.h> #include <unistd.h> #include <linux/android/binder_ctl.h> int main(int argc, char *argv[]) { int fd, ret, saved_errno; size_t len; struct binderfs_device device = { 0 }; if (argc < 2) exit(EXIT_FAILURE); len = strlen(argv[1]); if (len > BINDERFS_MAX_NAME) exit(EXIT_FAILURE); memcpy(device.name, argv[1], len); fd = open("/dev/binderfs/binder-control", O_RDONLY | O_CLOEXEC); if (fd < 0) { printf("%s - Failed to open binder-control device\n", strerror(errno)); exit(EXIT_FAILURE); } ret = ioctl(fd, BINDER_CTL_ADD, &device); saved_errno = errno; close(fd); errno = saved_errno; if (ret < 0) { printf("%s - Failed to allocate new binder device\n", strerror(errno)); exit(EXIT_FAILURE); } printf("Allocated new binder device with major %d, minor %d, and " "name %s\n", device.major, device.minor, device.name); exit(EXIT_SUCCESS); } Cc: Martijn Coenen <maco@android.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com> Acked-by: Todd Kjos <tkjos@google.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |