CVE-2026-52943

pskb_carve_inside_header() and pskb_carve_inside_nonlinear() both copy the old skb_shared_info header into a new buffer via memcpy(), which includes the destructor_arg pointer (uarg) for MSG_ZEROCOPY skbs. Neither function calls net_zcopy_get() for the new shinfo, creating an unaccounted holder: every skb_shared_info with destructor_arg set will call skb_zcopy_clear() once when freed, but the corresponding net_zcopy_get() was never called for the new copy. Repeated calls drive uarg->refcnt to zero prematurely, freeing ubuf_info_msgzc while TX skbs still hold live destructor_arg pointers.

KASAN reports use-after-free on a freed ubuf_info_msgzc:

BUG: KASAN: slab-use-after-free in skb_release_data+0x77b/0x810 Read of size 8 at addr ffff88801574d3e8 by task poc/220

Call Trace: skb_release_data+0x77b/0x810 kfree_skb_list_reason+0x13e/0x610 skb_release_data+0x4cd/0x810 sk_skb_reason_drop+0xf3/0x340 skb_queue_purge_reason+0x282/0x440 rds_tcp_inc_free+0x1e/0x30 rds_recvmsg+0x354/0x1780 __sys_recvmsg+0xdf/0x180

Allocated by task 219: msg_zerocopy_realloc+0x157/0x7b0 tcp_sendmsg_locked+0x2892/0x3ba0

Freed by task 219: ip_recv_error+0x74a/0xb10 tcp_recvmsg+0x475/0x530

The skb consuming the late access still referenced the same uarg via shinfo->destructor_arg copied by pskb_carve_inside_nonlinear() without a refcount bump. This has been verified to be reliably exploitable: a working proof-of-concept achieves full root privilege escalation from an unprivileged local user on a default kernel configuration.

The fix follows the pattern of pskb_expand_head() which has the same memcpy/cloned structure. For pskb_carve_inside_header(), net_zcopy_get() is placed after skb_orphan_frags() succeeds, so the orphan error path needs no cleanup. For pskb_carve_inside_nonlinear(), net_zcopy_get() is placed after all failure points and just before skb_release_data(), so no error path needs cleanup at all -- matching pskb_expand_head() more closely and avoiding the need for a balancing net_zcopy_put().

Database specific

{
    "cna_assigner":  "Linux",
    "osv_generated_from":  "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/52xxx/CVE-2026-52943.json"
}

References

Affected packages

Git / git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git

Affected ranges

Type: GIT
Repo: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
Events: Introduced

6fa01ccd883021105e9f8af7d04b9f156fa3494a

Fixed

8dbed691e43a50903658130bde0fcb5abc425b37

Fixed

9b40bdc2a3298225dffab8158208a0d8c6300578

Fixed

fd470f0a97b8e9a125f520265d2f3b088ffb5b8a

Fixed

ceafb893b12f23331dcc5ff9587e643c3a40ee9f

Fixed

2e0e74c59b2761a414d9f48d7bee1e45220b2427

Fixed

96a4713ae041cc85e712bac682cd2e644004d6c6

Fixed

474d6c771d798bca84f0a140b611e36743511e18

Fixed

98d0912e9f841e5529a5b89a972805f34cb1c69d

Database specific

source

"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2026-52943.json"

Linux / Kernel

Package

Name: Kernel

Affected ranges

Type: ECOSYSTEM
Events: Introduced

4.7.0

Fixed

5.10.259

Type: ECOSYSTEM
Events: Introduced

5.11.0

Fixed

5.15.210

Type: ECOSYSTEM
Events: Introduced

5.16.0

Fixed

6.1.176

Type: ECOSYSTEM
Events: Introduced

6.2.0

Fixed

6.6.143

Type: ECOSYSTEM
Events: Introduced

6.7.0

Fixed

6.12.93

Type: ECOSYSTEM
Events: Introduced

6.13.0

Fixed

6.18.35

Type: ECOSYSTEM
Events: Introduced

6.19.0

Fixed

7.0.12

Database specific

source

"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2026-52943.json"