i2c: smbus: reject oversized block transfers in the common path

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-93287
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-24 17:17:09 UTC
Updated2026-10-03 11:17:47 UTC
DescriptionIn 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.

Risk And Classification

Primary CVSS: v3.1 7.8 HIGH from 416baaa9-dc9f-4396-8d5f-8c081fb06d67

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

EPSS: 0.001290000 probability, percentile 0.021790000 (date 2026-10-05)

VersionSourceTypeScoreSeverityVector
3.1416baaa9-dc9f-4396-8d5f-8c081fb06d67Secondary7.8HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
3.1CNADECLARED7.8HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

CVSS v3.1 Breakdown

Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 4710317891e4824ce1510a6b5066abbd3e917750 856dffcc097b3d8ed45a643ebda07cb92968cb33 git Not specified
CNA Linux Linux affected 4710317891e4824ce1510a6b5066abbd3e917750 356875e33f2c6d2061a02c9dec1a1e639d265a55 git Not specified
CNA Linux Linux affected 4710317891e4824ce1510a6b5066abbd3e917750 72ca5e0b8b7a62615758f8871c34d61616c2dc8b git Not specified
CNA Linux Linux affected 4710317891e4824ce1510a6b5066abbd3e917750 df077253f6405d67ad087538e495ef32a05717b7 git Not specified
CNA Linux Linux affected 4710317891e4824ce1510a6b5066abbd3e917750 f09edffba97d37b1fdff5f818a9a45f8a98ac171 git Not specified
CNA Linux Linux affected 4710317891e4824ce1510a6b5066abbd3e917750 c4b478bc50b7ca9865e237909941253a0f7111a2 git Not specified
CNA Linux Linux affected 4710317891e4824ce1510a6b5066abbd3e917750 3051cd060fa496df42954291fa2306ed2eab4ecc git Not specified
CNA Linux Linux affected 2.6.33 Not specified
CNA Linux Linux unaffected 2.6.33 semver Not specified
CNA Linux Linux unaffected 5.10.271 5.10.* semver Not specified
CNA Linux Linux unaffected 5.15.222 5.15.* semver Not specified
CNA Linux Linux unaffected 6.1.189 6.1.* semver Not specified
CNA Linux Linux unaffected 6.6.158 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.111 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.53 6.18.* semver Not specified
CNA Linux Linux unaffected 7.1 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/f09edffba97d37b1fdff5f818a9a45f8a98ac171 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/72ca5e0b8b7a62615758f8871c34d61616c2dc8b 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/856dffcc097b3d8ed45a643ebda07cb92968cb33 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/356875e33f2c6d2061a02c9dec1a1e639d265a55 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/c4b478bc50b7ca9865e237909941253a0f7111a2 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/3051cd060fa496df42954291fa2306ed2eab4ecc 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/df077253f6405d67ad087538e495ef32a05717b7 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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