| 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-2021-46933: usb: gadget: f_fs: Clear ffs_eventfd in ffs_data_clear. |
| |
| Description |
| =========== |
| |
| In the Linux kernel, the following vulnerability has been resolved: |
| |
| usb: gadget: f_fs: Clear ffs_eventfd in ffs_data_clear. |
| |
| ffs_data_clear is indirectly called from both ffs_fs_kill_sb and |
| ffs_ep0_release, so it ends up being called twice when userland closes ep0 |
| and then unmounts f_fs. |
| If userland provided an eventfd along with function's USB descriptors, it |
| ends up calling eventfd_ctx_put as many times, causing a refcount |
| underflow. |
| NULL-ify ffs_eventfd to prevent these extraneous eventfd_ctx_put calls. |
| |
| Also, set epfiles to NULL right after de-allocating it, for readability. |
| |
| For completeness, ffs_data_clear actually ends up being called thrice, the |
| last call being before the whole ffs structure gets freed, so when this |
| specific sequence happens there is a second underflow happening (but not |
| being reported): |
| |
| /sys/kernel/debug/tracing# modprobe usb_f_fs |
| /sys/kernel/debug/tracing# echo ffs_data_clear > set_ftrace_filter |
| /sys/kernel/debug/tracing# echo function > current_tracer |
| /sys/kernel/debug/tracing# echo 1 > tracing_on |
| (setup gadget, run and kill function userland process, teardown gadget) |
| /sys/kernel/debug/tracing# echo 0 > tracing_on |
| /sys/kernel/debug/tracing# cat trace |
| smartcard-openp-436 [000] ..... 1946.208786: ffs_data_clear <-ffs_data_closed |
| smartcard-openp-431 [000] ..... 1946.279147: ffs_data_clear <-ffs_data_closed |
| smartcard-openp-431 [000] .n... 1946.905512: ffs_data_clear <-ffs_data_put |
| |
| Warning output corresponding to above trace: |
| [ 1946.284139] WARNING: CPU: 0 PID: 431 at lib/refcount.c:28 refcount_warn_saturate+0x110/0x15c |
| [ 1946.293094] refcount_t: underflow; use-after-free. |
| [ 1946.298164] Modules linked in: usb_f_ncm(E) u_ether(E) usb_f_fs(E) hci_uart(E) btqca(E) btrtl(E) btbcm(E) btintel(E) bluetooth(E) nls_ascii(E) nls_cp437(E) vfat(E) fat(E) bcm2835_v4l2(CE) bcm2835_mmal_vchiq(CE) videobuf2_vmalloc(E) videobuf2_memops(E) sha512_generic(E) videobuf2_v4l2(E) sha512_arm(E) videobuf2_common(E) videodev(E) cpufreq_dt(E) snd_bcm2835(CE) brcmfmac(E) mc(E) vc4(E) ctr(E) brcmutil(E) snd_soc_core(E) snd_pcm_dmaengine(E) drbg(E) snd_pcm(E) snd_timer(E) snd(E) soundcore(E) drm_kms_helper(E) cec(E) ansi_cprng(E) rc_core(E) syscopyarea(E) raspberrypi_cpufreq(E) sysfillrect(E) sysimgblt(E) cfg80211(E) max17040_battery(OE) raspberrypi_hwmon(E) fb_sys_fops(E) regmap_i2c(E) ecdh_generic(E) rfkill(E) ecc(E) bcm2835_rng(E) rng_core(E) vchiq(CE) leds_gpio(E) libcomposite(E) fuse(E) configfs(E) ip_tables(E) x_tables(E) autofs4(E) ext4(E) crc16(E) mbcache(E) jbd2(E) crc32c_generic(E) sdhci_iproc(E) sdhci_pltfm(E) sdhci(E) |
| [ 1946.399633] CPU: 0 PID: 431 Comm: smartcard-openp Tainted: G C OE 5.15.0-1-rpi #1 Debian 5.15.3-1 |
| [ 1946.417950] Hardware name: BCM2835 |
| [ 1946.425442] Backtrace: |
| [ 1946.432048] [<c08d60a0>] (dump_backtrace) from [<c08d62ec>] (show_stack+0x20/0x24) |
| [ 1946.448226] r7:00000009 r6:0000001c r5:c04a948c r4:c0a64e2c |
| [ 1946.458412] [<c08d62cc>] (show_stack) from [<c08d9ae0>] (dump_stack+0x28/0x30) |
| [ 1946.470380] [<c08d9ab8>] (dump_stack) from [<c0123500>] (__warn+0xe8/0x154) |
| [ 1946.482067] r5:c04a948c r4:c0a71dc8 |
| [ 1946.490184] [<c0123418>] (__warn) from [<c08d6948>] (warn_slowpath_fmt+0xa0/0xe4) |
| [ 1946.506758] r7:00000009 r6:0000001c r5:c0a71dc8 r4:c0a71e04 |
| [ 1946.517070] [<c08d68ac>] (warn_slowpath_fmt) from [<c04a948c>] (refcount_warn_saturate+0x110/0x15c) |
| [ 1946.535309] r8:c0100224 r7:c0dfcb84 r6:ffffffff r5:c3b84c00 r4:c24a17c0 |
| [ 1946.546708] [<c04a937c>] (refcount_warn_saturate) from [<c0380134>] (eventfd_ctx_put+0x48/0x74) |
| [ 1946.564476] [<c03800ec>] (eventfd_ctx_put) from [<bf5464e8>] (ffs_data_clear+0xd0/0x118 [usb_f_fs]) |
| [ 1946.582664] r5:c3b84c00 r4:c2695b00 |
| [ 1946.590668] [<bf546418>] (ffs_data_clear [usb_f_fs]) from [<bf547cc0>] (ffs_data_closed+0x9c/0x150 [usb_f_fs]) |
| [ 1946.609608] r5:bf54d014 r4:c2695b00 |
| [ 1946.617522] [<bf547c24>] (ffs_data_closed [usb_f_fs]) from [<bf547da0>] (ffs_fs_kill_sb+0x2c/0x30 [usb_f_fs]) |
| [ 1946.636217] r7:c0dfcb84 r6:c3a12260 r5:bf54d014 r4:c229f000 |
| [ 1946.646273] [<bf547d74>] (ffs_fs_kill_sb [usb_f_fs]) from [<c0326d50>] (deactivate_locked_super+0x54/0x9c) |
| [ 1946.664893] r5:bf54d014 r4:c229f000 |
| [ 1946.672921] [<c0326cfc>] (deactivate_locked_super) from [<c0326df8>] (deactivate_super+0x60/0x64) |
| [ 1946.690722] r5:c2a09000 r4:c229f000 |
| [ 1946.698706] [<c0326d98>] (deactivate_super) from [<c0349a28>] (cleanup_mnt+0xe4/0x14c) |
| [ 1946.715553] r5:c2a09000 r4:00000000 |
| [ 1946.723528] [<c0349944>] (cleanup_mnt) from [<c0349b08>] (__cleanup_mnt+0x1c/0x20) |
| [ 1946.739922] r7:c0dfcb84 r6:c3a12260 r5:c3a126fc r4:00000000 |
| [ 1946.750088] [<c0349aec>] (__cleanup_mnt) from [<c0143d10>] (task_work_run+0x84/0xb8) |
| [ 1946.766602] [<c0143c8c>] (task_work_run) from [<c010bdc8>] (do_work_pending+0x470/0x56c) |
| [ 1946.783540] r7:5ac3c35a r6:c0d0424c r5:c200bfb0 r4:c200a000 |
| [ 1946.793614] [<c010b958>] (do_work_pending) from [<c01000c0>] (slow_work_pending+0xc/0x20) |
| [ 1946.810553] Exception stack(0xc200bfb0 to 0xc200bff8) |
| [ 1946.820129] bfa0: 00000000 00000000 000000aa b5e21430 |
| [ 1946.837104] bfc0: bef867a0 00000001 bef86840 00000034 bef86838 bef86790 bef86794 bef867a0 |
| [ 1946.854125] bfe0: 00000000 bef86798 b67b7a1c b6d626a4 60000010 b5a23760 |
| [ 1946.865335] r10:00000000 r9:c200a000 r8:c0100224 r7:00000034 r6:bef86840 r5:00000001 |
| [ 1946.881914] r4:bef867a0 |
| [ 1946.888793] ---[ end trace 7387f2a9725b28d0 ]--- |
| |
| The Linux kernel CVE team has assigned CVE-2021-46933 to this issue. |
| |
| |
| Affected and fixed versions |
| =========================== |
| |
| Issue introduced in 4.0 with commit 5e33f6fdf735cda1d4580fe6f1878da05718fe73 and fixed in 4.4.298 with commit f976dd7011150244a7ba820f2c331e9fb253befa |
| Issue introduced in 4.0 with commit 5e33f6fdf735cda1d4580fe6f1878da05718fe73 and fixed in 4.9.296 with commit cc8c8028c21b2a3842a1e98e99e55028df275919 |
| Issue introduced in 4.0 with commit 5e33f6fdf735cda1d4580fe6f1878da05718fe73 and fixed in 4.14.261 with commit 52500239e3f2d6fc77b6f58632a9fb98fe74ac09 |
| Issue introduced in 4.0 with commit 5e33f6fdf735cda1d4580fe6f1878da05718fe73 and fixed in 4.19.224 with commit 33f6a0cbb7772146e1c11f38028fffbfed14728b |
| Issue introduced in 4.0 with commit 5e33f6fdf735cda1d4580fe6f1878da05718fe73 and fixed in 5.4.170 with commit 240fc586e83d645912accce081a48aa63a45f6ee |
| Issue introduced in 4.0 with commit 5e33f6fdf735cda1d4580fe6f1878da05718fe73 and fixed in 5.10.90 with commit 1c4ace3e6b8575745c50dca9e76e0021e697d645 |
| Issue introduced in 4.0 with commit 5e33f6fdf735cda1d4580fe6f1878da05718fe73 and fixed in 5.15.13 with commit ebef2aa29f370b5096c16020c104e393192ef684 |
| Issue introduced in 4.0 with commit 5e33f6fdf735cda1d4580fe6f1878da05718fe73 and fixed in 5.16 with commit b1e0887379422975f237d43d8839b751a6bcf154 |
| |
| 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-2021-46933 |
| 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/usb/gadget/function/f_fs.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/f976dd7011150244a7ba820f2c331e9fb253befa |
| https://git.kernel.org/stable/c/cc8c8028c21b2a3842a1e98e99e55028df275919 |
| https://git.kernel.org/stable/c/52500239e3f2d6fc77b6f58632a9fb98fe74ac09 |
| https://git.kernel.org/stable/c/33f6a0cbb7772146e1c11f38028fffbfed14728b |
| https://git.kernel.org/stable/c/240fc586e83d645912accce081a48aa63a45f6ee |
| https://git.kernel.org/stable/c/1c4ace3e6b8575745c50dca9e76e0021e697d645 |
| https://git.kernel.org/stable/c/ebef2aa29f370b5096c16020c104e393192ef684 |
| https://git.kernel.org/stable/c/b1e0887379422975f237d43d8839b751a6bcf154 |
