Bug 2536660 (CVE-2026-93174)

Summary: CVE-2026-93174 kernel: bpf: Copy per-CPU map value padding in copy_map_value_long()
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: akhatavk, aos-team-art-private, asdas, dpaolell, jdelft, jupierce, lgarciaa, mbiarnes, ppalepu, ppostler, prdhamdh, rhel-process-autobot, sghai, sidsharm, suppawar, vlaad, watson-tool-maintainers
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's BPF (Berkeley Packet Filter) subsystem. When handling per-CPU map elements, the `copy_map_value_long()` function incorrectly copies only the `map->value_size` instead of the full allocated size, which includes padding. This oversight can lead to user-space applications, through UAPI lookup operations or `bpf_iter`, receiving uninitialized or stale heap memory contents from the uncopied padding. This could result in information disclosure.
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Description OSIDB Bzimport 2026-09-17 19:03:08 UTC 
In the Linux kernel, the following vulnerability has been resolved:

bpf: Copy per-CPU map value padding in copy_map_value_long()

In kernel, per-CPU map elements are stored with
round_up(map->value_size, 8) bytes. On UAPI lookup paths, it copies the
rounded size for each CPU into a temporary buffer.

However, copy_map_value_long() passes 'map->value_size' to
bpf_obj_memcpy(). When the map has special fields, bpf_obj_memcpy() copies
around those fields with memcpy(), and does not copy the tail padding
between 'map->value_size' and round_up(map->value_size, 8).

The temporary UAPI lookup buffers are allocated without __GFP_ZERO. As a
result, when the per-CPU map's value size is not equal to
round_up(map->value_size, 8), UAPI LOOKUP_ELEM and its variants can return
stale heap contents from that padding to user space. The same issue
applies to bpf_iter for per-CPU maps.

Pass round_up(map->value_size, 8) to bpf_obj_memcpy() from
copy_map_value_long(), so per-CPU maps both with and without special
fields copy the entire per-CPU slot. Remove the now redundant round_up()
from bpf_obj_memcpy()'s long_memcpy path.
Comment 1 gkamathe 2026-09-18 05:44:02 UTC 
Upstream advisory:
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-93174.mbox