CVE-2026-52993: tipc: fix double-free in tipc_buf_append()

CVE-2026-52993: tipc: fix double-free in tipc_buf_append()

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

tipc: fix double-free in tipc_buf_append()

tipc_msg_validate() can potentially reallocate the skb it is validating,
freeing the old one.  In tipc_buf_append(), it was being called with a
pointer to a local variable which was a copy of the caller's skb
pointer.

If the skb was reallocated and validation subsequently failed, the error
handling path would free the original skb pointer, which had already
been freed, leading to double-free.

Fix this by checking if head now points to a newly allocated reassembled
skb.  If it does, reassign *headbuf for later freeing operations.

The Linux kernel CVE team has assigned CVE-2026-52993 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 4.15 with commit d618d09a68e4eed7a435beb2e355250f6f40664a and fixed in 5.10.258 with commit a438975a6dcdbd70865978c021650d1485586f0b
	Issue introduced in 4.15 with commit d618d09a68e4eed7a435beb2e355250f6f40664a and fixed in 5.15.209 with commit 4ee4deadaae7cb2e3d53af0fc889cf92a73413c0
	Issue introduced in 4.15 with commit d618d09a68e4eed7a435beb2e355250f6f40664a and fixed in 6.1.175 with commit d3556656c6daebf8def751c7e71d11dd0a180d24
	Issue introduced in 4.15 with commit d618d09a68e4eed7a435beb2e355250f6f40664a and fixed in 6.6.141 with commit 0274f24485fc38032d4093e463dc3ff5c7a667c9
	Issue introduced in 4.15 with commit d618d09a68e4eed7a435beb2e355250f6f40664a and fixed in 6.12.91 with commit 4d104882bc815d4ec666ace9155f5f52715879a6
	Issue introduced in 4.15 with commit d618d09a68e4eed7a435beb2e355250f6f40664a and fixed in 6.18.33 with commit 1d5e589055880fae229e229e1929e087dbe08cf3
	Issue introduced in 4.15 with commit d618d09a68e4eed7a435beb2e355250f6f40664a and fixed in 7.0.10 with commit 29940fff14110ca48c5ccc168d121665b51bb778
	Issue introduced in 4.15 with commit d618d09a68e4eed7a435beb2e355250f6f40664a and fixed in 7.1 with commit d293ca716e7d5dffdaecaf6b9b2f857a33dc3d3a

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-52993
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	net/tipc/msg.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/a438975a6dcdbd70865978c021650d1485586f0b
	https://git.kernel.org/stable/c/4ee4deadaae7cb2e3d53af0fc889cf92a73413c0
	https://git.kernel.org/stable/c/d3556656c6daebf8def751c7e71d11dd0a180d24
	https://git.kernel.org/stable/c/0274f24485fc38032d4093e463dc3ff5c7a667c9
	https://git.kernel.org/stable/c/4d104882bc815d4ec666ace9155f5f52715879a6
	https://git.kernel.org/stable/c/1d5e589055880fae229e229e1929e087dbe08cf3
	https://git.kernel.org/stable/c/29940fff14110ca48c5ccc168d121665b51bb778
	https://git.kernel.org/stable/c/d293ca716e7d5dffdaecaf6b9b2f857a33dc3d3a