{"id":"CVE-2026-43472","state":"PUBLISHED","title":"unshare: fix unshare_fs() handling","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nunshare: fix unshare_fs() handling\n\nThere's an unpleasant corner case in unshare(2), when we have a\nCLONE_NEWNS in flags and current->fs hadn't been shared at all; in that\ncase copy_mnt_ns() gets passed current->fs instead of a private copy,\nwhich causes interesting warts in proof of correctness]\n\n> I guess if private means fs->users == 1, the condition could still be true.\n\nUnfortunately, it's worse than just a convoluted proof of correctness.\nConsider the case when we have CLONE_NEWCGROUP in addition to CLONE_NEWNS\n(and current->fs->users == 1).\n\nWe pass current->fs to copy_mnt_ns(), all right.  Suppose it succeeds and\nflips current->fs->{pwd,root} to corresponding locations in the new namespace.\nNow we proceed to copy_cgroup_ns(), which fails (e.g. with -ENOMEM).\nWe call put_mnt_ns() on the namespace created by copy_mnt_ns(), it's\ndestroyed and its mount tree is dissolved, but...  current->fs->root and\ncurrent->fs->pwd are both left pointing to now detached mounts.\n\nThey are pinning those, so it's not a UAF, but it leaves the calling\nprocess with unshare(2) failing with -ENOMEM _and_ leaving it with\npwd and root on detached isolated mounts.  The last part is clearly a bug.\n\nThere is other fun related to that mess (races with pivot_root(), including\nthe one between pivot_root() and fork(), of all things), but this one\nis easy to isolate and fix - treat CLONE_NEWNS as \"allocate a new\nfs_struct even if it hadn't been shared in the first place\".  Sure, we could\ngo for something like \"if both CLONE_NEWNS *and* one of the things that might\nend up failing after copy_mnt_ns() call in create_new_namespaces() are set,\nforce allocation of new fs_struct\", but let's keep it simple - the cost\nof copy_fs_struct() is trivial.\n\nAnother benefit is that copy_mnt_ns() with CLONE_NEWNS *always* gets\na freshly allocated fs_struct, yet to be attached to anything.  That\nseriously simplifies the analysis...\n\nFWIW, that bug had been there since the introduction of unshare(2) ;-/","publishedAt":"2026-05-08T14:22:31.556Z","updatedAt":"2026-05-11T22:25:16.258Z","severity":null,"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"741a295130606143edbf9fc740f633dbc1e6225f","status":"affected","lessThan":"845bf3c6963a52096d0d3866e4a92db77a0c03d8","versionType":"git"},{"version":"741a295130606143edbf9fc740f633dbc1e6225f","status":"affected","lessThan":"d3ffc8f13034af895531a02c30b1fe3a34b46432","versionType":"git"},{"version":"741a295130606143edbf9fc740f633dbc1e6225f","status":"affected","lessThan":"d0d99f60538ddb4a62ccaac2168d8f448965f083","versionType":"git"},{"version":"741a295130606143edbf9fc740f633dbc1e6225f","status":"affected","lessThan":"d7963d6997fea86a6def242ac36198b86655f912","versionType":"git"},{"version":"741a295130606143edbf9fc740f633dbc1e6225f","status":"affected","lessThan":"aa9ebc084505fb26dd90f4d7a249045aad152043","versionType":"git"},{"version":"741a295130606143edbf9fc740f633dbc1e6225f","status":"affected","lessThan":"af8f4be3b68ac8caa41c8e5ead0eeaf5e85e42d0","versionType":"git"},{"version":"741a295130606143edbf9fc740f633dbc1e6225f","status":"affected","lessThan":"42e21e74061b0ebbd859839f81acf10efad02a27","versionType":"git"},{"version":"741a295130606143edbf9fc740f633dbc1e6225f","status":"affected","lessThan":"6c4b2243cb6c0755159bd567130d5e12e7b10d9f","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["kernel/fork.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"2.6.16","status":"affected"},{"version":"0","status":"unaffected","lessThan":"2.6.16","versionType":"semver"},{"version":"5.10.253","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.203","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.167","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.130","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.78","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.19","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"6.19.9","status":"unaffected","lessThanOrEqual":"6.19.*","versionType":"semver"},{"version":"7.0","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["kernel/fork.c"]}],"references":["https://git.kernel.org/stable/c/845bf3c6963a52096d0d3866e4a92db77a0c03d8","https://git.kernel.org/stable/c/d3ffc8f13034af895531a02c30b1fe3a34b46432","https://git.kernel.org/stable/c/d0d99f60538ddb4a62ccaac2168d8f448965f083","https://git.kernel.org/stable/c/d7963d6997fea86a6def242ac36198b86655f912","https://git.kernel.org/stable/c/aa9ebc084505fb26dd90f4d7a249045aad152043","https://git.kernel.org/stable/c/af8f4be3b68ac8caa41c8e5ead0eeaf5e85e42d0","https://git.kernel.org/stable/c/42e21e74061b0ebbd859839f81acf10efad02a27","https://git.kernel.org/stable/c/6c4b2243cb6c0755159bd567130d5e12e7b10d9f"],"weaknesses":[],"ingestedAt":"2026-10-29T20:11:57.932Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/43xxx/CVE-2026-43472.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-43472","state":"PUBLISHED","datePublished":"2026-05-08T14:22:31.556Z","dateUpdated":"2026-05-11T22:25:16.258Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-05-01T14:12:56.011Z"},"containers":{"cna":{"title":"unshare: fix unshare_fs() handling","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nunshare: fix unshare_fs() handling\n\nThere's an unpleasant corner case in unshare(2), when we have a\nCLONE_NEWNS in flags and current->fs hadn't been shared at all; in that\ncase copy_mnt_ns() gets passed current->fs instead of a private copy,\nwhich causes interesting warts in proof of correctness]\n\n> I guess if private means fs->users == 1, the condition could still be true.\n\nUnfortunately, it's worse than just a convoluted proof of correctness.\nConsider the case when we have CLONE_NEWCGROUP in addition to CLONE_NEWNS\n(and current->fs->users == 1).\n\nWe pass current->fs to copy_mnt_ns(), all right.  Suppose it succeeds and\nflips current->fs->{pwd,root} to corresponding locations in the new namespace.\nNow we proceed to copy_cgroup_ns(), which fails (e.g. with -ENOMEM).\nWe call put_mnt_ns() on the namespace created by copy_mnt_ns(), it's\ndestroyed and its mount tree is dissolved, but...  current->fs->root and\ncurrent->fs->pwd are both left pointing to now detached mounts.\n\nThey are pinning those, so it's not a UAF, but it leaves the calling\nprocess with unshare(2) failing with -ENOMEM _and_ leaving it with\npwd and root on detached isolated mounts.  The last part is clearly a bug.\n\nThere is other fun related to that mess (races with pivot_root(), including\nthe one between pivot_root() and fork(), of all things), but this one\nis easy to isolate and fix - treat CLONE_NEWNS as \"allocate a new\nfs_struct even if it hadn't been shared in the first place\".  Sure, we could\ngo for something like \"if both CLONE_NEWNS *and* one of the things that might\nend up failing after copy_mnt_ns() call in create_new_namespaces() are set,\nforce allocation of new fs_struct\", but let's keep it simple - the cost\nof copy_fs_struct() is trivial.\n\nAnother benefit is that copy_mnt_ns() with CLONE_NEWNS *always* gets\na freshly allocated fs_struct, yet to be attached to anything.  That\nseriously simplifies the analysis...\n\nFWIW, that bug had been there since the introduction of unshare(2) ;-/"}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"741a295130606143edbf9fc740f633dbc1e6225f","status":"affected","lessThan":"845bf3c6963a52096d0d3866e4a92db77a0c03d8","versionType":"git"},{"version":"741a295130606143edbf9fc740f633dbc1e6225f","status":"affected","lessThan":"d3ffc8f13034af895531a02c30b1fe3a34b46432","versionType":"git"},{"version":"741a295130606143edbf9fc740f633dbc1e6225f","status":"affected","lessThan":"d0d99f60538ddb4a62ccaac2168d8f448965f083","versionType":"git"},{"version":"741a295130606143edbf9fc740f633dbc1e6225f","status":"affected","lessThan":"d7963d6997fea86a6def242ac36198b86655f912","versionType":"git"},{"version":"741a295130606143edbf9fc740f633dbc1e6225f","status":"affected","lessThan":"aa9ebc084505fb26dd90f4d7a249045aad152043","versionType":"git"},{"version":"741a295130606143edbf9fc740f633dbc1e6225f","status":"affected","lessThan":"af8f4be3b68ac8caa41c8e5ead0eeaf5e85e42d0","versionType":"git"},{"version":"741a295130606143edbf9fc740f633dbc1e6225f","status":"affected","lessThan":"42e21e74061b0ebbd859839f81acf10efad02a27","versionType":"git"},{"version":"741a295130606143edbf9fc740f633dbc1e6225f","status":"affected","lessThan":"6c4b2243cb6c0755159bd567130d5e12e7b10d9f","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["kernel/fork.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"2.6.16","status":"affected"},{"version":"0","status":"unaffected","lessThan":"2.6.16","versionType":"semver"},{"version":"5.10.253","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.203","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.167","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.130","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.78","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.19","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"6.19.9","status":"unaffected","lessThanOrEqual":"6.19.*","versionType":"semver"},{"version":"7.0","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["kernel/fork.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/845bf3c6963a52096d0d3866e4a92db77a0c03d8"},{"url":"https://git.kernel.org/stable/c/d3ffc8f13034af895531a02c30b1fe3a34b46432"},{"url":"https://git.kernel.org/stable/c/d0d99f60538ddb4a62ccaac2168d8f448965f083"},{"url":"https://git.kernel.org/stable/c/d7963d6997fea86a6def242ac36198b86655f912"},{"url":"https://git.kernel.org/stable/c/aa9ebc084505fb26dd90f4d7a249045aad152043"},{"url":"https://git.kernel.org/stable/c/af8f4be3b68ac8caa41c8e5ead0eeaf5e85e42d0"},{"url":"https://git.kernel.org/stable/c/42e21e74061b0ebbd859839f81acf10efad02a27"},{"url":"https://git.kernel.org/stable/c/6c4b2243cb6c0755159bd567130d5e12e7b10d9f"}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-05-11T22:25:16.258Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.16","versionEndExcluding":"5.10.253"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.16","versionEndExcluding":"5.15.203"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.16","versionEndExcluding":"6.1.167"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.16","versionEndExcluding":"6.6.130"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.16","versionEndExcluding":"6.12.78"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.16","versionEndExcluding":"6.18.19"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.16","versionEndExcluding":"6.19.9"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.16","versionEndExcluding":"7.0"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}