Bug 2521057 (CVE-2026-74582)

Summary: CVE-2026-74582 kernel: packet: use consistent hard_header_len in non-ring send paths
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
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Priority: high    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's packet handling functions, specifically packet_snd() and packet_sendmsg_spkt(). This vulnerability arises from inconsistent handling of network device header lengths during packet construction. A local attacker could exploit this by triggering a race condition during device reconfiguration, leading to an out-of-bounds write. This could potentially allow for privilege escalation or arbitrary code execution.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Description OSIDB Bzimport 2026-08-21 17:03:47 UTC 
In the Linux kernel, the following vulnerability has been resolved:

packet: use consistent hard_header_len in non-ring send paths

packet_snd() reads dev->hard_header_len multiple times while allocating
and constructing an skb. Device reconfiguration can change this value
concurrently, for example through bonding device type changes.

For SOCK_RAW, packet_snd() can save a larger value in reserve and later
allocate headroom using a smaller value. Moving skb->data back by reserve
then places it before skb->head, and the following copy from userspace can
attempt an out-of-bounds write.

packet_sendmsg_spkt() has the same issue because it calculates its
reservation and header offset from separate reads before dropping the RCU
read lock to allocate the skb.

Add LL_RESERVED_SPACE_EX() for callers that already saved a header length.
Read hard_header_len once in packet_snd() and use it for allocation and
construction. In packet_sendmsg_spkt(), preserve the allocation-time value
through the device lookup retry.

The separate SOCK_DGRAM consistency problem between hard_header_len and
header_ops->create is not addressed here.
Comment 1 Mauro Matteo Cascella 2026-08-21 17:49:32 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026082100-CVE-2026-74582-3296@gregkh/T