bpf: Reject narrower access to pointer ctx fields
The following BPF program, simplified from a syzkaller repro, causes a
kernel warning:
r0 = *(u8 *)(r1 + 169);
exit;
With pointer field sk being at offset 168 in __sk_buff. This access is
detected as a narrower read in bpf_skb_is_valid_access because it
doesn't match offsetof(struct __sk_buff, sk). It is therefore allowed
and later proceeds to bpf_convert_ctx_access. Note that for the
"is_narrower_load" case in the convert_ctx_accesses(), the insn->off
is aligned, so the cnt may not be 0 because it matches the
offsetof(struct __sk_buff, sk) in the bpf_convert_ctx_access. However,
the target_size stays 0 and the verifier errors with a kernel warning:
verifier bug: error during ctx access conversion(1)
This patch fixes that to return a proper "invalid bpf_context access
off=X size=Y" error on the load instruction.
The same issue affects multiple other fields in context structures that
allow narrow access. Some other non-affected fields (for sk_msg,
sk_lookup, and sockopt) were also changed to use bpf_ctx_range_ptr for
consistency.
Note this syzkaller crash was reported in the "Closes" link below, which
used to be about a different bug, fixed in
commit fce7bd8e385a ("bpf/verifier: Handle BPF_LOAD_ACQ instructions
in insn_def_regno()"). Because syzbot somehow confused the two bugs,
the new crash and repro didn't get reported to the mailing list.
Analysis and contextual insights are available on OpenCVE Cloud.
No vendor fix or workaround currently provided.
Additional remediation guidance may be available on OpenCVE Cloud.
Tracking
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| Source | ID | Title |
|---|---|---|
Debian DLA |
DLA-4475-1 | linux security update |
Debian DLA |
DLA-4476-1 | linux-6.1 security update |
Debian DSA |
DSA-6126-1 | linux security update |
Debian DSA |
DSA-6127-1 | linux security update |
EUVD |
EUVD-2025-27920 | In the Linux kernel, the following vulnerability has been resolved: bpf: Reject narrower access to pointer ctx fields The following BPF program, simplified from a syzkaller repro, causes a kernel warning: r0 = *(u8 *)(r1 + 169); exit; With pointer field sk being at offset 168 in __sk_buff. This access is detected as a narrower read in bpf_skb_is_valid_access because it doesn't match offsetof(struct __sk_buff, sk). It is therefore allowed and later proceeds to bpf_convert_ctx_access. Note that for the "is_narrower_load" case in the convert_ctx_accesses(), the insn->off is aligned, so the cnt may not be 0 because it matches the offsetof(struct __sk_buff, sk) in the bpf_convert_ctx_access. However, the target_size stays 0 and the verifier errors with a kernel warning: verifier bug: error during ctx access conversion(1) This patch fixes that to return a proper "invalid bpf_context access off=X size=Y" error on the load instruction. The same issue affects multiple other fields in context structures that allow narrow access. Some other non-affected fields (for sk_msg, sk_lookup, and sockopt) were also changed to use bpf_ctx_range_ptr for consistency. Note this syzkaller crash was reported in the "Closes" link below, which used to be about a different bug, fixed in commit fce7bd8e385a ("bpf/verifier: Handle BPF_LOAD_ACQ instructions in insn_def_regno()"). Because syzbot somehow confused the two bugs, the new crash and repro didn't get reported to the mailing list. |
Ubuntu USN |
USN-8162-1 | Linux kernel (NVIDIA Tegra) vulnerabilities |
Ubuntu USN |
USN-8180-1 | Linux kernel vulnerabilities |
Ubuntu USN |
USN-8180-2 | Linux kernel (FIPS) vulnerabilities |
Ubuntu USN |
USN-8186-1 | Linux kernel (Real-time) vulnerabilities |
Ubuntu USN |
USN-8187-1 | Linux kernel (NVIDIA) vulnerabilities |
Ubuntu USN |
USN-8188-1 | Linux kernel (HWE) vulnerabilities |
Ubuntu USN |
USN-8180-3 | Linux kernel vulnerabilities |
Ubuntu USN |
USN-8180-4 | Linux kernel (Azure FIPS) vulnerabilities |
Ubuntu USN |
USN-8180-5 | Linux kernel (IBM) vulnerabilities |
Ubuntu USN |
USN-8243-1 | Linux kernel (Azure) vulnerabilities |
Ubuntu USN |
USN-8180-6 | Linux kernel (Raspberry Pi) vulnerabilities |
Ubuntu USN |
USN-8275-1 | Linux kernel (Xilinx ZynqMP) vulnerabilities |
Ubuntu USN |
USN-8278-1 | Linux kernel vulnerabilities |
Ubuntu USN |
USN-8289-1 | Linux kernel (NVIDIA) vulnerabilities |
Ubuntu USN |
USN-8296-1 | Linux kernel (FIPS) vulnerabilities |
Fri, 06 Feb 2026 16:45:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| References |
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Fri, 23 Jan 2026 10:45:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| References |
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Wed, 26 Nov 2025 18:00:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Weaknesses | NVD-CWE-noinfo | |
| CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* |
Thu, 21 Aug 2025 12:45:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| First Time appeared |
Linux
Linux linux Kernel |
|
| Vendors & Products |
Linux
Linux linux Kernel |
Wed, 20 Aug 2025 12:15:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| References |
| |
| Metrics |
threat_severity
|
cvssV3_1
|
Tue, 19 Aug 2025 17:15:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | In the Linux kernel, the following vulnerability has been resolved: bpf: Reject narrower access to pointer ctx fields The following BPF program, simplified from a syzkaller repro, causes a kernel warning: r0 = *(u8 *)(r1 + 169); exit; With pointer field sk being at offset 168 in __sk_buff. This access is detected as a narrower read in bpf_skb_is_valid_access because it doesn't match offsetof(struct __sk_buff, sk). It is therefore allowed and later proceeds to bpf_convert_ctx_access. Note that for the "is_narrower_load" case in the convert_ctx_accesses(), the insn->off is aligned, so the cnt may not be 0 because it matches the offsetof(struct __sk_buff, sk) in the bpf_convert_ctx_access. However, the target_size stays 0 and the verifier errors with a kernel warning: verifier bug: error during ctx access conversion(1) This patch fixes that to return a proper "invalid bpf_context access off=X size=Y" error on the load instruction. The same issue affects multiple other fields in context structures that allow narrow access. Some other non-affected fields (for sk_msg, sk_lookup, and sockopt) were also changed to use bpf_ctx_range_ptr for consistency. Note this syzkaller crash was reported in the "Closes" link below, which used to be about a different bug, fixed in commit fce7bd8e385a ("bpf/verifier: Handle BPF_LOAD_ACQ instructions in insn_def_regno()"). Because syzbot somehow confused the two bugs, the new crash and repro didn't get reported to the mailing list. | |
| Title | bpf: Reject narrower access to pointer ctx fields | |
| References |
|
Status: PUBLISHED
Assigner: Linux
Published:
Updated: 2026-05-11T21:31:12.628Z
Reserved: 2025-04-16T04:51:24.026Z
Link: CVE-2025-38591
No data.
Status : Analyzed
Published: 2025-08-19T17:15:36.790
Modified: 2026-03-17T16:09:47.267
Link: CVE-2025-38591
OpenCVE Enrichment
Updated: 2025-08-21T12:31:54Z
Debian DLA
Debian DSA
EUVD
Ubuntu USN