CVE-2021-46933
usb: gadget: f_fs: Clear ffs_eventfd in ffs_data_clear.
Severity Score
Exploit Likelihood
Affected Versions
Public Exploits
0Exploited in Wild
-Decision
Descriptions
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:c0dfcb
---truncated---
En el kernel de Linux se ha resuelto la siguiente vulnerabilidad: usb: gadget: f_fs: Borrar ffs_eventfd en ffs_data_clear. ffs_data_clear se llama indirectamente desde ffs_fs_kill_sb y ffs_ep0_release, por lo que termina siendo llamado dos veces cuando el área de usuario cierra ep0 y luego desmonta f_fs. Si Userland proporcionó un eventfd junto con los descriptores USB de la función, termina llamando a eventfd_ctx_put tantas veces, provocando un desbordamiento insuficiente de recuento. NULL-ify ffs_eventfd para evitar estas llamadas extrañas eventfd_ctx_put. Además, establezca epfiles en NULL justo después de desasignarlo, para facilitar la lectura. Para completar, ffs_data_clear en realidad termina siendo llamado tres veces, la última llamada es antes de que se libere toda la estructura de ffs, por lo que cuando ocurre esta secuencia específica, se produce un segundo desbordamiento insuficiente (pero no se informa): /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 (dispositivo de configuración, función ejecutar y finalizar proceso de usuario, dispositivo de desmontaje) /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 tarjeta inteligente -openp-431 [000] ..... 1946.279147: ffs_data_clear <-ffs_data_closed smartcard-openp-431 [000] .n... 1946.905512: ffs_data_clear <-ffs_data_put Salida de advertencia correspondiente al seguimiento anterior: [ 1946.284139] ADVERTENCIA: CPU : 0 PID: 431 en lib/refcount.c:28 refcount_warn_saturate+0x110/0x15c [ 1946.293094] refcount_t: desbordamiento insuficiente; use-after-free. [1946.298164] Módulos vinculados en: 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_b cm2835 (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: tarjeta inteligente- openp Contaminado: GC OE 5.15.0-1-rpi #1 Debian 5.15.3-1 [ 1946.417950] Nombre de hardware: BCM2835 [ 1946.425442] Seguimiento inverso: [ 1946.432048] [] (dump_backtrace) de [] ( show_stack+0x20/0x24) [ 1946.448226] r7:00000009 r6:0000001c r5:c04a948c r4:c0a64e2c [ 1946.458412] [] (show_stack) de [] (dump_ pila+0x28/0x30) [ 1946.470380] [< c08d9ab8>] (dump_stack) de [] (__warn+0xe8/0x154) [ 1946.482067] r5:c04a948c r4:c0a71dc8 [ 1946.490184] [] (__warn) de [] (warn_slowpath_fmt+0xa0/ 0xe4) [ 1946.506758] r7:00000009 r6:0000001c r5:c0a71dc8 r4:c0a71e04 [ 1946.517070] [] (warn_slowpath_fmt) de [] (refcount_war n_saturado+0x110/0x15c) [ 1946.535309] r8:c0100224 r7:c0dfcb84 r6:ffffffff r5:c3b84c00 r4:c24a17c0 [ 1946.546708] [] (refcount_warn_saturate) de [] (eventfd_ctx_put+0x48/0x74) [ 1946.564476] [] (eventfd_ctx_put) de [] (ffs_data_clear+0xd0/0x118 [usb_f_fs]) [ 1946.582664] r5:c3b84c00 r4:c2695b00 [ 1946.590668] [] (ffs_data_clear [usb_f_fs]) de [] ( ffs_data_closed+0x9c/0x150 [usb_f_fs]) [ 1946.609608] r5:bf54d014 r4:c2695b00 [ 1946.617522] [] (ffs_data_closed [usb_f_fs
CVSS Scores
SSVC
- Decision:Track
Timeline
- 2024-02-25 CVE Reserved
- 2024-02-27 CVE Published
- 2024-04-21 EPSS Updated
- 2024-12-19 CVE Updated
- ---------- Exploited in Wild
- ---------- KEV Due Date
- ---------- First Exploit
CWE
- CWE-416: Use After Free
CAPEC
References (9)
URL | Tag | Source |
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https://git.kernel.org/stable/c/5e33f6fdf735cda1d4580fe6f1878da05718fe73 | Vuln. Introduced |
URL | Date | SRC |
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URL | Date | SRC |
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Affected Vendors, Products, and Versions
Vendor | Product | Version | Other | Status | ||||||
---|---|---|---|---|---|---|---|---|---|---|
Vendor | Product | Version | Other | Status | <-- --> | Vendor | Product | Version | Other | Status |
Linux Search vendor "Linux" | Linux Kernel Search vendor "Linux" for product "Linux Kernel" | >= 4.0 < 4.4.298 Search vendor "Linux" for product "Linux Kernel" and version " >= 4.0 < 4.4.298" | en |
Affected
| ||||||
Linux Search vendor "Linux" | Linux Kernel Search vendor "Linux" for product "Linux Kernel" | >= 4.0 < 4.9.296 Search vendor "Linux" for product "Linux Kernel" and version " >= 4.0 < 4.9.296" | en |
Affected
| ||||||
Linux Search vendor "Linux" | Linux Kernel Search vendor "Linux" for product "Linux Kernel" | >= 4.0 < 4.14.261 Search vendor "Linux" for product "Linux Kernel" and version " >= 4.0 < 4.14.261" | en |
Affected
| ||||||
Linux Search vendor "Linux" | Linux Kernel Search vendor "Linux" for product "Linux Kernel" | >= 4.0 < 4.19.224 Search vendor "Linux" for product "Linux Kernel" and version " >= 4.0 < 4.19.224" | en |
Affected
| ||||||
Linux Search vendor "Linux" | Linux Kernel Search vendor "Linux" for product "Linux Kernel" | >= 4.0 < 5.4.170 Search vendor "Linux" for product "Linux Kernel" and version " >= 4.0 < 5.4.170" | en |
Affected
| ||||||
Linux Search vendor "Linux" | Linux Kernel Search vendor "Linux" for product "Linux Kernel" | >= 4.0 < 5.10.90 Search vendor "Linux" for product "Linux Kernel" and version " >= 4.0 < 5.10.90" | en |
Affected
| ||||||
Linux Search vendor "Linux" | Linux Kernel Search vendor "Linux" for product "Linux Kernel" | >= 4.0 < 5.15.13 Search vendor "Linux" for product "Linux Kernel" and version " >= 4.0 < 5.15.13" | en |
Affected
| ||||||
Linux Search vendor "Linux" | Linux Kernel Search vendor "Linux" for product "Linux Kernel" | >= 4.0 < 5.16 Search vendor "Linux" for product "Linux Kernel" and version " >= 4.0 < 5.16" | en |
Affected
|