| From bippy-5f407fcff5a0 Mon Sep 17 00:00:00 2001 |
| From: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| To: <linux-cve-announce@vger.kernel.org> |
| Reply-to: <cve@kernel.org>, <linux-kernel@vger.kernel.org> |
| Subject: CVE-2021-47634: ubi: Fix race condition between ctrl_cdev_ioctl and ubi_cdev_ioctl |
| |
| Description |
| =========== |
| |
| In the Linux kernel, the following vulnerability has been resolved: |
| |
| ubi: Fix race condition between ctrl_cdev_ioctl and ubi_cdev_ioctl |
| |
| Hulk Robot reported a KASAN report about use-after-free: |
| ================================================================== |
| BUG: KASAN: use-after-free in __list_del_entry_valid+0x13d/0x160 |
| Read of size 8 at addr ffff888035e37d98 by task ubiattach/1385 |
| [...] |
| Call Trace: |
| klist_dec_and_del+0xa7/0x4a0 |
| klist_put+0xc7/0x1a0 |
| device_del+0x4d4/0xed0 |
| cdev_device_del+0x1a/0x80 |
| ubi_attach_mtd_dev+0x2951/0x34b0 [ubi] |
| ctrl_cdev_ioctl+0x286/0x2f0 [ubi] |
| |
| Allocated by task 1414: |
| device_add+0x60a/0x18b0 |
| cdev_device_add+0x103/0x170 |
| ubi_create_volume+0x1118/0x1a10 [ubi] |
| ubi_cdev_ioctl+0xb7f/0x1ba0 [ubi] |
| |
| Freed by task 1385: |
| cdev_device_del+0x1a/0x80 |
| ubi_remove_volume+0x438/0x6c0 [ubi] |
| ubi_cdev_ioctl+0xbf4/0x1ba0 [ubi] |
| [...] |
| ================================================================== |
| |
| The lock held by ctrl_cdev_ioctl is ubi_devices_mutex, but the lock held |
| by ubi_cdev_ioctl is ubi->device_mutex. Therefore, the two locks can be |
| concurrent. |
| |
| ctrl_cdev_ioctl contains two operations: ubi_attach and ubi_detach. |
| ubi_detach is bug-free because it uses reference counting to prevent |
| concurrency. However, uif_init and uif_close in ubi_attach may race with |
| ubi_cdev_ioctl. |
| |
| uif_init will race with ubi_cdev_ioctl as in the following stack. |
| cpu1 cpu2 cpu3 |
| _______________________|________________________|______________________ |
| ctrl_cdev_ioctl |
| ubi_attach_mtd_dev |
| uif_init |
| ubi_cdev_ioctl |
| ubi_create_volume |
| cdev_device_add |
| ubi_add_volume |
| // sysfs exist |
| kill_volumes |
| ubi_cdev_ioctl |
| ubi_remove_volume |
| cdev_device_del |
| // first free |
| ubi_free_volume |
| cdev_del |
| // double free |
| cdev_device_del |
| |
| And uif_close will race with ubi_cdev_ioctl as in the following stack. |
| cpu1 cpu2 cpu3 |
| _______________________|________________________|______________________ |
| ctrl_cdev_ioctl |
| ubi_attach_mtd_dev |
| uif_init |
| ubi_cdev_ioctl |
| ubi_create_volume |
| cdev_device_add |
| ubi_debugfs_init_dev |
| //error goto out_uif; |
| uif_close |
| kill_volumes |
| ubi_cdev_ioctl |
| ubi_remove_volume |
| cdev_device_del |
| // first free |
| ubi_free_volume |
| // double free |
| |
| The cause of this problem is that commit 714fb87e8bc0 make device |
| "available" before it becomes accessible via sysfs. Therefore, we |
| roll back the modification. We will fix the race condition between |
| ubi device creation and udev by removing ubi_get_device in |
| vol_attribute_show and dev_attribute_show.This avoids accessing |
| uninitialized ubi_devices[ubi_num]. |
| |
| ubi_get_device is used to prevent devices from being deleted during |
| sysfs execution. However, now kernfs ensures that devices will not |
| be deleted before all reference counting are released. |
| The key process is shown in the following stack. |
| |
| device_del |
| device_remove_attrs |
| device_remove_groups |
| sysfs_remove_groups |
| sysfs_remove_group |
| remove_files |
| kernfs_remove_by_name |
| kernfs_remove_by_name_ns |
| __kernfs_remove |
| kernfs_drain |
| |
| The Linux kernel CVE team has assigned CVE-2021-47634 to this issue. |
| |
| |
| Affected and fixed versions |
| =========================== |
| |
| Issue introduced in 4.8 with commit 714fb87e8bc05ff78255afc0dca981e8c5242785 and fixed in 4.14.276 with commit f149b1bd213820363731aa119e5011ca892a2aac |
| Issue introduced in 4.8 with commit 714fb87e8bc05ff78255afc0dca981e8c5242785 and fixed in 4.19.238 with commit a8ecee49259f8f78d91ddb329ab2be7e6fd01974 |
| Issue introduced in 4.8 with commit 714fb87e8bc05ff78255afc0dca981e8c5242785 and fixed in 5.4.189 with commit d727fd32cbd1abf3465f607021bc9c746f17b5a8 |
| Issue introduced in 4.8 with commit 714fb87e8bc05ff78255afc0dca981e8c5242785 and fixed in 5.10.110 with commit 432b057f8e847ae5a2306515606f8d2defaca178 |
| Issue introduced in 4.8 with commit 714fb87e8bc05ff78255afc0dca981e8c5242785 and fixed in 5.15.33 with commit 1a3f1cf87054833242fcd0218de0481cf855f888 |
| Issue introduced in 4.8 with commit 714fb87e8bc05ff78255afc0dca981e8c5242785 and fixed in 5.16.19 with commit c32fe764191b8ae8b128588beb96e3718d9179d8 |
| Issue introduced in 4.8 with commit 714fb87e8bc05ff78255afc0dca981e8c5242785 and fixed in 5.17.2 with commit 5f9e9c223e48c264241d2f34d0bfc29e5fcb5c1b |
| Issue introduced in 4.8 with commit 714fb87e8bc05ff78255afc0dca981e8c5242785 and fixed in 5.18 with commit 3cbf0e392f173ba0ce425968c8374a6aa3e90f2e |
| Issue introduced in 3.2.84 with commit 016820bde3f0895d09fcad370415085ba0d1bd4a |
| Issue introduced in 3.10.103 with commit 12f567db822241090b90c5645ea9146f6cf8fa42 |
| Issue introduced in 3.12.63 with commit 31b0fca8ab9b9786fe6e5027c4a8587b47db5abf |
| Issue introduced in 3.14.77 with commit 6117840dec60344167038f9511c3770d4c096eaa |
| Issue introduced in 3.16.39 with commit bd7d3de27e7e1acce2e276074a498a82e0834663 |
| Issue introduced in 3.18.40 with commit cdf25333b42fb889f086ef65d0734d0dbdc49f4e |
| Issue introduced in 4.1.31 with commit ae32d1b98ba29408df87c0ed47877ca0f248eae7 |
| Issue introduced in 4.4.19 with commit 4056337b1e81a1b137aa562133dc5430cd2fd19e |
| Issue introduced in 4.7.2 with commit f3db4c640b32485105554e0bfd16bbde585f6fb0 |
| |
| Please see https://www.kernel.org for a full list of currently supported |
| kernel versions by the kernel community. |
| |
| Unaffected versions might change over time as fixes are backported to |
| older supported kernel versions. The official CVE entry at |
| https://cve.org/CVERecord/?id=CVE-2021-47634 |
| will be updated if fixes are backported, please check that for the most |
| up to date information about this issue. |
| |
| |
| Affected files |
| ============== |
| |
| The file(s) affected by this issue are: |
| drivers/mtd/ubi/build.c |
| drivers/mtd/ubi/vmt.c |
| |
| |
| Mitigation |
| ========== |
| |
| The Linux kernel CVE team recommends that you update to the latest |
| stable kernel version for this, and many other bugfixes. Individual |
| changes are never tested alone, but rather are part of a larger kernel |
| release. Cherry-picking individual commits is not recommended or |
| supported by the Linux kernel community at all. If however, updating to |
| the latest release is impossible, the individual changes to resolve this |
| issue can be found at these commits: |
| https://git.kernel.org/stable/c/f149b1bd213820363731aa119e5011ca892a2aac |
| https://git.kernel.org/stable/c/a8ecee49259f8f78d91ddb329ab2be7e6fd01974 |
| https://git.kernel.org/stable/c/d727fd32cbd1abf3465f607021bc9c746f17b5a8 |
| https://git.kernel.org/stable/c/432b057f8e847ae5a2306515606f8d2defaca178 |
| https://git.kernel.org/stable/c/1a3f1cf87054833242fcd0218de0481cf855f888 |
| https://git.kernel.org/stable/c/c32fe764191b8ae8b128588beb96e3718d9179d8 |
| https://git.kernel.org/stable/c/5f9e9c223e48c264241d2f34d0bfc29e5fcb5c1b |
| https://git.kernel.org/stable/c/3cbf0e392f173ba0ce425968c8374a6aa3e90f2e |
