CVE-2026-74400: bpf: fix crash in bpf_[set|remove]_dentry_xattr for negative dentries

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

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

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

bpf: fix crash in bpf_[set|remove]_dentry_xattr for negative dentries

bpf_set_dentry_xattr and bpf_remove_dentry_xattr BPF kfuncs attempt to
lock the inode of the supplied dentry without checking if it is
NULL. If a negative dentry is passed (e.g. from
security_inode_create), d_inode(dentry) returns NULL, and
inode_lock(inode) will cause a NULL pointer dereference.

Trivially fix this by adding a NULL check for inode before attempting
to lock it, returning -EINVAL if it is NULL.

Additionally, drop WARN_ON(!inode) in bpf_xattr_read_permission() and
bpf_xattr_write_permission(). These warnings could be triggered by
passing a negative dentry to bpf_get_dentry_xattr() or the _locked
variants of the xattr kfuncs, potentially causing a Denial of Service
on systems with panic_on_warn enabled. Instead, simply return -EINVAL.

The Linux kernel CVE team has assigned CVE-2026-74400 to this issue.


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

	Issue introduced in 6.15 with commit 56467292794b800164df20c076c409ac548e56ec and fixed in 6.18.40 with commit e003f3a4be738f650e283e92d07017c3fef8da52
	Issue introduced in 6.15 with commit 56467292794b800164df20c076c409ac548e56ec and fixed in 7.1.5 with commit 0160edf2af51c5fde742973742c5d10497901b21
	Issue introduced in 6.15 with commit 56467292794b800164df20c076c409ac548e56ec and fixed in 7.2-rc1 with commit 07410646f6ff1d23222f105ccab778957d401bbe

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-2026-74400
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:
	fs/bpf_fs_kfuncs.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/e003f3a4be738f650e283e92d07017c3fef8da52
	https://git.kernel.org/stable/c/0160edf2af51c5fde742973742c5d10497901b21
	https://git.kernel.org/stable/c/07410646f6ff1d23222f105ccab778957d401bbe