CVE-2026-74578: crypto: algif_skcipher - force synchronous processing on trees without ctx->state

From: Greg Kroah-Hartman <[email protected]>

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

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

crypto: algif_skcipher - force synchronous processing on trees without ctx->state

The AIO/async path in skcipher_recvmsg() passes the socket-wide ctx->iv
directly into the skcipher request. After io_submit() the socket lock is
dropped and the request is processed asynchronously, so a concurrent
sendmsg(ALG_SET_IV) can overwrite ctx->iv and make the in-flight request
run under an attacker-controlled IV. For CTR/stream modes this is
IV/keystream reuse and lets an unprivileged user recover the plaintext of
a concurrent operation.

Snapshotting ctx->iv into per-request storage for the async path is not
sufficient. For ciphers with statesize == 0 - which includes cbc and ctr -
the MSG_MORE inter-chunk IV chaining is carried solely by the in-place
req->iv writeback, which a snapshot redirects into per-request memory that
af_alg_free_resources() releases on completion, silently producing wrong
output. Writing the IV back from the completion callback instead is not
possible either: that would require lock_sock() there, but the callback can
run in softirq/atomic context, so it must not sleep.

Make the operation synchronous instead, which removes both the IV race and
any writeback race. This is equivalent to the upstream resolution, commit
fcc77d33a34c ("net: Remove support for AIO on sockets"), which removed the
AIO socket path across net/ entirely and so produces the same end state for
this file. This patch deviates from that commit deliberately: rather than
removing AIO socket support tree-wide, which would be far too invasive for
stable, it removes only the AIO branch in crypto/algif_skcipher.c.
io_submit() now completes synchronously; AF_ALG async is rarely used in
practice.

The -EIOCBQUEUED check in skcipher_recvmsg() is now dead but harmless,
and is left alone to keep the fix minimal.

Tested on 6.6.y: attacker IV injection dropped from 2296/200000 to 0/200000
after the change; MSG_MORE chunked CTR output bit-identical to single-shot.

The Linux kernel CVE team has assigned CVE-2026-74578 to this issue.


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

	Issue introduced in 4.14 with commit e870456d8e7c8d57c059ea479b5aadbb55ff4c3a and fixed in 5.10.261 with commit bf09b0be8e851f050e98da702d247c14d81b591a
	Issue introduced in 4.14 with commit e870456d8e7c8d57c059ea479b5aadbb55ff4c3a and fixed in 5.15.212 with commit 73dd3bf704ca6c20639de70c08e9a10bee904a95
	Issue introduced in 4.14 with commit e870456d8e7c8d57c059ea479b5aadbb55ff4c3a and fixed in 6.1.178 with commit f1a87ca0843d74482402a206ea2dfb315ee9acbd
	Issue introduced in 4.14 with commit e870456d8e7c8d57c059ea479b5aadbb55ff4c3a and fixed in 6.6.145 with commit 7b91e51d0eb7cbb07f7f086f9176bd93dbbc85dd
	Issue introduced in 4.14 with commit e870456d8e7c8d57c059ea479b5aadbb55ff4c3a and fixed in 6.12.97 with commit 60eafc7b08c6689ea3ad39eff8d97aefc8a087c7
	Issue introduced in 4.14 with commit e870456d8e7c8d57c059ea479b5aadbb55ff4c3a and fixed in 6.18.40 with commit d7860b682da55433b5da0591b0e4c1982ecd2689
	Issue introduced in 4.14 with commit e870456d8e7c8d57c059ea479b5aadbb55ff4c3a and fixed in 7.1.5 with commit b05defc41b27c7d0c05c45f67bf5b91c28f93669
	Issue introduced in 4.14 with commit e870456d8e7c8d57c059ea479b5aadbb55ff4c3a and fixed in 7.2-rc1 with commit fcc77d33a34cf271702e8daafb6c593e4626776d

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-2026-74578
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:
	crypto/algif_skcipher.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/73dd3bf704ca6c20639de70c08e9a10bee904a95
	https://git.kernel.org/stable/c/f1a87ca0843d74482402a206ea2dfb315ee9acbd
	https://git.kernel.org/stable/c/7b91e51d0eb7cbb07f7f086f9176bd93dbbc85dd
	https://git.kernel.org/stable/c/60eafc7b08c6689ea3ad39eff8d97aefc8a087c7
	https://git.kernel.org/stable/c/d7860b682da55433b5da0591b0e4c1982ecd2689
	https://git.kernel.org/stable/c/b05defc41b27c7d0c05c45f67bf5b91c28f93669
	https://git.kernel.org/stable/c/fcc77d33a34cf271702e8daafb6c593e4626776d
	https://git.kernel.org/stable/c/bf09b0be8e851f050e98da702d247c14d81b591a