ghsa-w6v7-mjp2-pwcf
Vulnerability from github
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] [
{
"affected": [],
"aliases": [
"CVE-2021-46933"
],
"database_specific": {
"cwe_ids": [
"CWE-416"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2024-02-27T10:15:07Z",
"severity": "MODERATE"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nusb: gadget: f_fs: Clear ffs_eventfd in ffs_data_clear.\n\nffs_data_clear is indirectly called from both ffs_fs_kill_sb and\nffs_ep0_release, so it ends up being called twice when userland closes ep0\nand then unmounts f_fs.\nIf userland provided an eventfd along with function\u0027s USB descriptors, it\nends up calling eventfd_ctx_put as many times, causing a refcount\nunderflow.\nNULL-ify ffs_eventfd to prevent these extraneous eventfd_ctx_put calls.\n\nAlso, set epfiles to NULL right after de-allocating it, for readability.\n\nFor completeness, ffs_data_clear actually ends up being called thrice, the\nlast call being before the whole ffs structure gets freed, so when this\nspecific sequence happens there is a second underflow happening (but not\nbeing reported):\n\n/sys/kernel/debug/tracing# modprobe usb_f_fs\n/sys/kernel/debug/tracing# echo ffs_data_clear \u003e set_ftrace_filter\n/sys/kernel/debug/tracing# echo function \u003e current_tracer\n/sys/kernel/debug/tracing# echo 1 \u003e tracing_on\n(setup gadget, run and kill function userland process, teardown gadget)\n/sys/kernel/debug/tracing# echo 0 \u003e tracing_on\n/sys/kernel/debug/tracing# cat trace\n smartcard-openp-436 [000] ..... 1946.208786: ffs_data_clear \u003c-ffs_data_closed\n smartcard-openp-431 [000] ..... 1946.279147: ffs_data_clear \u003c-ffs_data_closed\n smartcard-openp-431 [000] .n... 1946.905512: ffs_data_clear \u003c-ffs_data_put\n\nWarning output corresponding to above trace:\n[ 1946.284139] WARNING: CPU: 0 PID: 431 at lib/refcount.c:28 refcount_warn_saturate+0x110/0x15c\n[ 1946.293094] refcount_t: underflow; use-after-free.\n[ 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)\n[ 1946.399633] CPU: 0 PID: 431 Comm: smartcard-openp Tainted: G C OE 5.15.0-1-rpi #1 Debian 5.15.3-1\n[ 1946.417950] Hardware name: BCM2835\n[ 1946.425442] Backtrace:\n[ 1946.432048] [\u003cc08d60a0\u003e] (dump_backtrace) from [\u003cc08d62ec\u003e] (show_stack+0x20/0x24)\n[ 1946.448226] r7:00000009 r6:0000001c r5:c04a948c r4:c0a64e2c\n[ 1946.458412] [\u003cc08d62cc\u003e] (show_stack) from [\u003cc08d9ae0\u003e] (dump_stack+0x28/0x30)\n[ 1946.470380] [\u003cc08d9ab8\u003e] (dump_stack) from [\u003cc0123500\u003e] (__warn+0xe8/0x154)\n[ 1946.482067] r5:c04a948c r4:c0a71dc8\n[ 1946.490184] [\u003cc0123418\u003e] (__warn) from [\u003cc08d6948\u003e] (warn_slowpath_fmt+0xa0/0xe4)\n[ 1946.506758] r7:00000009 r6:0000001c r5:c0a71dc8 r4:c0a71e04\n[ 1946.517070] [\u003cc08d68ac\u003e] (warn_slowpath_fmt) from [\u003cc04a948c\u003e] (refcount_warn_saturate+0x110/0x15c)\n[ 1946.535309] r8:c0100224 r7:c0dfcb84 r6:ffffffff r5:c3b84c00 r4:c24a17c0\n[ 1946.546708] [\u003cc04a937c\u003e] (refcount_warn_saturate) from [\u003cc0380134\u003e] (eventfd_ctx_put+0x48/0x74)\n[ 1946.564476] [\u003cc03800ec\u003e] (eventfd_ctx_put) from [\u003cbf5464e8\u003e] (ffs_data_clear+0xd0/0x118 [usb_f_fs])\n[ 1946.582664] r5:c3b84c00 r4:c2695b00\n[ 1946.590668] [\u003cbf546418\u003e] (ffs_data_clear [usb_f_fs]) from [\u003cbf547cc0\u003e] (ffs_data_closed+0x9c/0x150 [usb_f_fs])\n[ 1946.609608] r5:bf54d014 r4:c2695b00\n[ 1946.617522] [\u003cbf547c24\u003e] (ffs_data_closed [usb_f_fs]) from [\u003cbf547da0\u003e] (ffs_fs_kill_sb+0x2c/0x30 [usb_f_fs])\n[ 1946.636217] r7:c0dfcb\n---truncated---",
"id": "GHSA-w6v7-mjp2-pwcf",
"modified": "2024-04-10T21:30:28Z",
"published": "2024-02-27T12:31:10Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2021-46933"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/1c4ace3e6b8575745c50dca9e76e0021e697d645"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/240fc586e83d645912accce081a48aa63a45f6ee"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/33f6a0cbb7772146e1c11f38028fffbfed14728b"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/52500239e3f2d6fc77b6f58632a9fb98fe74ac09"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/b1e0887379422975f237d43d8839b751a6bcf154"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/cc8c8028c21b2a3842a1e98e99e55028df275919"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/ebef2aa29f370b5096c16020c104e393192ef684"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/f976dd7011150244a7ba820f2c331e9fb253befa"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
"type": "CVSS_V3"
}
]
}
Sightings
| Author | Source | Type | Date |
|---|
Nomenclature
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