In the Linux kernel, the following vulnerability has been resolved:
unshare: fix unshare_fs() handling
There's an unpleasant corner case in unshare(2), when we have a
CLONE_NEWNS in flags and current->fs hadn't been shared at all; in that
case copy_mnt_ns() gets passed current->fs instead of a private copy,
which causes interesting warts in proof of correctness]
> I guess if private means fs->users == 1, the condition could still be true.
Unfortunately, it's worse than just a convoluted proof of correctness.
Consider the case when we have CLONE_NEWCGROUP in addition to CLONE_NEWNS
(and current->fs->users == 1).
We pass current->fs to copy_mnt_ns(), all right. Suppose it succeeds and
flips current->fs->{pwd,root} to corresponding locations in the new namespace.
Now we proceed to copy_cgroup_ns(), which fails (e.g. with -ENOMEM).
We call put_mnt_ns() on the namespace created by copy_mnt_ns(), it's
destroyed and its mount tree is dissolved, but... current->fs->root and
current->fs->pwd are both left pointing to now detached mounts.
They are pinning those, so it's not a UAF, but it leaves the calling
process with unshare(2) failing with -ENOMEM _and_ leaving it with
pwd and root on detached isolated mounts. The last part is clearly a bug.
There is other fun related to that mess (races with pivot_root(), including
the one between pivot_root() and fork(), of all things), but this one
is easy to isolate and fix - treat CLONE_NEWNS as "allocate a new
fs_struct even if it hadn't been shared in the first place". Sure, we could
go for something like "if both CLONE_NEWNS *and* one of the things that might
end up failing after copy_mnt_ns() call in create_new_namespaces() are set,
force allocation of new fs_struct", but let's keep it simple - the cost
of copy_fs_struct() is trivial.
Another benefit is that copy_mnt_ns() with CLONE_NEWNS *always* gets
a freshly allocated fs_struct, yet to be attached to anything. That
seriously simplifies the analysis...
FWIW, that bug had been there since the introduction of unshare(2) ;-/
References
Configurations
Configuration 1 (hide)
|
History
21 May 2026, 14:59
| Type | Values Removed | Values Added |
|---|---|---|
| CPE |
21 May 2026, 13:37
| Type | Values Removed | Values Added |
|---|---|---|
| First Time |
Linux linux Kernel
Linux |
|
| CPE | cpe:2.3:o:linux:linux_kernel:2.6.16:rc4:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:2.6.16:rc6:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:2.6.16:rc3:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:2.6.16:-:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:2.6.16:rc5:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:7.0:rc2:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:2.6.16:rc7:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:7.0:rc1:*:*:*:*:*:* |
|
| References | () https://git.kernel.org/stable/c/42e21e74061b0ebbd859839f81acf10efad02a27 - Patch | |
| References | () https://git.kernel.org/stable/c/6c4b2243cb6c0755159bd567130d5e12e7b10d9f - Patch | |
| References | () https://git.kernel.org/stable/c/845bf3c6963a52096d0d3866e4a92db77a0c03d8 - Patch | |
| References | () https://git.kernel.org/stable/c/aa9ebc084505fb26dd90f4d7a249045aad152043 - Patch | |
| References | () https://git.kernel.org/stable/c/af8f4be3b68ac8caa41c8e5ead0eeaf5e85e42d0 - Patch | |
| References | () https://git.kernel.org/stable/c/d0d99f60538ddb4a62ccaac2168d8f448965f083 - Patch | |
| References | () https://git.kernel.org/stable/c/d3ffc8f13034af895531a02c30b1fe3a34b46432 - Patch | |
| References | () https://git.kernel.org/stable/c/d7963d6997fea86a6def242ac36198b86655f912 - Patch | |
| CWE | CWE-908 | |
| CVSS |
v2 : v3 : |
v2 : unknown
v3 : 5.5 |
08 May 2026, 15:17
| Type | Values Removed | Values Added |
|---|---|---|
| New CVE |
Information
Published : 2026-05-08 15:17
Updated : 2026-05-21 14:59
NVD link : CVE-2026-43472
Mitre link : CVE-2026-43472
CVE.ORG link : CVE-2026-43472
JSON object : View
Products Affected
linux
- linux_kernel
CWE
CWE-908
Use of Uninitialized Resource