In the Linux kernel, the following vulnerability has been resolved:
i2c: smbus: reject oversized block transfers in the common path
The SMBus block transfer length data->block[0] is validated in
i2c_smbus_xfer_emulated() but that check runs too late for tracepoints
and is skipped entirely when the adapter provides a native smbus_xfer
implementation. This allows user-controlled oversized block lengths to
reach tracepoint memcpy calls and driver callbacks unchecked.
Add an early validation in __i2c_smbus_xfer() that rejects block
transfers whose caller-supplied length is zero or exceeds
I2C_SMBUS_BLOCK_MAX before any tracepoint fires or driver callback
runs. data->block[0] is filled in by the device on SMBus block reads,
so the check is scoped to operations where the length is actually
supplied by the caller. This is consistent with the existing -EINVAL
convention in the emulated path and protects all downstream consumers
at once: the smbus_write tracepoint, all native smbus_xfer driver
implementations, and the emulated path.
Two distinct bugs are fixed by this change:
Bug 1: smbus_write tracepoint OOB (include/trace/events/smbus.h)
trace_smbus_write() fires before any validation and copies
data->block[0]+1 bytes into a 34-byte event buffer. With
block[0]=0xfe the tracepoint copies 255 bytes, overflowing by 221.
BUG: KASAN: stack-out-of-bounds in trace_event_raw_event_smbus_write+0x27c/0x530
Read of size 255 at addr ffff88800d98fcf8 by task poc_smbus/91
Call Trace:
<TASK>
__asan_memcpy+0x23/0x80
trace_event_raw_event_smbus_write+0x27c/0x530
__i2c_smbus_xfer+0x43a/0xa40
i2c_smbus_xfer+0x19e/0x340
i2cdev_ioctl_smbus+0x38f/0x7f0
i2cdev_ioctl+0x35e/0x680
__x64_sys_ioctl+0x147/0x1e0
do_syscall_64+0xcf/0x15a0
entry_SYSCALL_64_after_hwframe+0x76/0x7e
</TASK>
Bug 2: i2c-stub I2C_SMBUS_I2C_BLOCK_DATA OOB (drivers/i2c/i2c-stub.c)
stub_xfer() implements .smbus_xfer directly and only clamps
block[0] against 256-command, not I2C_SMBUS_BLOCK_MAX. With
block[0]=0xff and command=0 the loop accesses block[1+i] for
i up to 254, far past the 34-byte union.
UBSAN: array-index-out-of-bounds in drivers/i2c/i2c-stub.c:223:44
index 34 is out of range for type '__u8 [34]'
Call Trace:
<TASK>
__ubsan_handle_out_of_bounds+0xd7/0x120
stub_xfer+0x1971/0x198f [i2c_stub]
__i2c_smbus_xfer+0x306/0xa40
i2c_smbus_xfer+0x19e/0x340
i2cdev_ioctl_smbus+0x38f/0x7f0
i2cdev_ioctl+0x35e/0x680
__x64_sys_ioctl+0x147/0x1e0
do_syscall_64+0xcf/0x15a0
entry_SYSCALL_64_after_hwframe+0x76/0x7e
</TASK>
Both traces reproduced on v7.0-rc6+i2c/for-current with KASAN+UBSAN.
i2c: smbus: reject oversized block transfers in the common path
The SMBus block transfer length data->block[0] is validated in
i2c_smbus_xfer_emulated() but that check runs too late for tracepoints
and is skipped entirely when the adapter provides a native smbus_xfer
implementation. This allows user-controlled oversized block lengths to
reach tracepoint memcpy calls and driver callbacks unchecked.
Add an early validation in __i2c_smbus_xfer() that rejects block
transfers whose caller-supplied length is zero or exceeds
I2C_SMBUS_BLOCK_MAX before any tracepoint fires or driver callback
runs. data->block[0] is filled in by the device on SMBus block reads,
so the check is scoped to operations where the length is actually
supplied by the caller. This is consistent with the existing -EINVAL
convention in the emulated path and protects all downstream consumers
at once: the smbus_write tracepoint, all native smbus_xfer driver
implementations, and the emulated path.
Two distinct bugs are fixed by this change:
Bug 1: smbus_write tracepoint OOB (include/trace/events/smbus.h)
trace_smbus_write() fires before any validation and copies
data->block[0]+1 bytes into a 34-byte event buffer. With
block[0]=0xfe the tracepoint copies 255 bytes, overflowing by 221.
BUG: KASAN: stack-out-of-bounds in trace_event_raw_event_smbus_write+0x27c/0x530
Read of size 255 at addr ffff88800d98fcf8 by task poc_smbus/91
Call Trace:
<TASK>
__asan_memcpy+0x23/0x80
trace_event_raw_event_smbus_write+0x27c/0x530
__i2c_smbus_xfer+0x43a/0xa40
i2c_smbus_xfer+0x19e/0x340
i2cdev_ioctl_smbus+0x38f/0x7f0
i2cdev_ioctl+0x35e/0x680
__x64_sys_ioctl+0x147/0x1e0
do_syscall_64+0xcf/0x15a0
entry_SYSCALL_64_after_hwframe+0x76/0x7e
</TASK>
Bug 2: i2c-stub I2C_SMBUS_I2C_BLOCK_DATA OOB (drivers/i2c/i2c-stub.c)
stub_xfer() implements .smbus_xfer directly and only clamps
block[0] against 256-command, not I2C_SMBUS_BLOCK_MAX. With
block[0]=0xff and command=0 the loop accesses block[1+i] for
i up to 254, far past the 34-byte union.
UBSAN: array-index-out-of-bounds in drivers/i2c/i2c-stub.c:223:44
index 34 is out of range for type '__u8 [34]'
Call Trace:
<TASK>
__ubsan_handle_out_of_bounds+0xd7/0x120
stub_xfer+0x1971/0x198f [i2c_stub]
__i2c_smbus_xfer+0x306/0xa40
i2c_smbus_xfer+0x19e/0x340
i2cdev_ioctl_smbus+0x38f/0x7f0
i2cdev_ioctl+0x35e/0x680
__x64_sys_ioctl+0x147/0x1e0
do_syscall_64+0xcf/0x15a0
entry_SYSCALL_64_after_hwframe+0x76/0x7e
</TASK>
Both traces reproduced on v7.0-rc6+i2c/for-current with KASAN+UBSAN.
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | ||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Linux | Linux | unaffected |
|
||||||||||||||||||
| Linux | Linux | affected |
|
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Fixes
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Workaround
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References
History
Thu, 24 Sep 2026 16:30:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | In the Linux kernel, the following vulnerability has been resolved: i2c: smbus: reject oversized block transfers in the common path The SMBus block transfer length data->block[0] is validated in i2c_smbus_xfer_emulated() but that check runs too late for tracepoints and is skipped entirely when the adapter provides a native smbus_xfer implementation. This allows user-controlled oversized block lengths to reach tracepoint memcpy calls and driver callbacks unchecked. Add an early validation in __i2c_smbus_xfer() that rejects block transfers whose caller-supplied length is zero or exceeds I2C_SMBUS_BLOCK_MAX before any tracepoint fires or driver callback runs. data->block[0] is filled in by the device on SMBus block reads, so the check is scoped to operations where the length is actually supplied by the caller. This is consistent with the existing -EINVAL convention in the emulated path and protects all downstream consumers at once: the smbus_write tracepoint, all native smbus_xfer driver implementations, and the emulated path. Two distinct bugs are fixed by this change: Bug 1: smbus_write tracepoint OOB (include/trace/events/smbus.h) trace_smbus_write() fires before any validation and copies data->block[0]+1 bytes into a 34-byte event buffer. With block[0]=0xfe the tracepoint copies 255 bytes, overflowing by 221. BUG: KASAN: stack-out-of-bounds in trace_event_raw_event_smbus_write+0x27c/0x530 Read of size 255 at addr ffff88800d98fcf8 by task poc_smbus/91 Call Trace: <TASK> __asan_memcpy+0x23/0x80 trace_event_raw_event_smbus_write+0x27c/0x530 __i2c_smbus_xfer+0x43a/0xa40 i2c_smbus_xfer+0x19e/0x340 i2cdev_ioctl_smbus+0x38f/0x7f0 i2cdev_ioctl+0x35e/0x680 __x64_sys_ioctl+0x147/0x1e0 do_syscall_64+0xcf/0x15a0 entry_SYSCALL_64_after_hwframe+0x76/0x7e </TASK> Bug 2: i2c-stub I2C_SMBUS_I2C_BLOCK_DATA OOB (drivers/i2c/i2c-stub.c) stub_xfer() implements .smbus_xfer directly and only clamps block[0] against 256-command, not I2C_SMBUS_BLOCK_MAX. With block[0]=0xff and command=0 the loop accesses block[1+i] for i up to 254, far past the 34-byte union. UBSAN: array-index-out-of-bounds in drivers/i2c/i2c-stub.c:223:44 index 34 is out of range for type '__u8 [34]' Call Trace: <TASK> __ubsan_handle_out_of_bounds+0xd7/0x120 stub_xfer+0x1971/0x198f [i2c_stub] __i2c_smbus_xfer+0x306/0xa40 i2c_smbus_xfer+0x19e/0x340 i2cdev_ioctl_smbus+0x38f/0x7f0 i2cdev_ioctl+0x35e/0x680 __x64_sys_ioctl+0x147/0x1e0 do_syscall_64+0xcf/0x15a0 entry_SYSCALL_64_after_hwframe+0x76/0x7e </TASK> Both traces reproduced on v7.0-rc6+i2c/for-current with KASAN+UBSAN. | |
| Title | i2c: smbus: reject oversized block transfers in the common path | |
| First Time appeared |
Linux
Linux linux Kernel |
|
| CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Linux
Linux linux Kernel |
|
| References |
|
Projects
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MITRE
Status: PUBLISHED
Assigner: Linux
Published:
Updated: 2026-09-24T16:02:11.296Z
Reserved: 2026-09-17T16:02:15.099Z
Link: CVE-2026-93287
Vulnrichment
No data.
NVD
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Redhat
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OpenCVE Enrichment
No data.
Weaknesses
No weakness.