{"id":"CVE-2026-74483","state":"PUBLISHED","title":"binfmt_misc: don't leak the user namespace when the mount fails","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nbinfmt_misc: don't leak the user namespace when the mount fails\n\nbm_get_tree() takes a reference to the user namespace and hands it to\nget_tree_keyed() as the sget key. sget_fc() moves that reference into\nsb->s_fs_info and clears fc->s_fs_info, so from that point on the\nsuperblock owns it and bm_free() doesn't see it anymore.\n\nThe superblock drops it in ->put_super(). But generic_shutdown_super()\nonly calls ->put_super() from inside the if (sb->s_root) branch, so\nnothing releases it when bm_fill_super() fails:\n\n- The kzalloc_obj() failure leaves s_root NULL and the whole branch is\n  skipped.\n\n- A simple_fill_super() failure in the file loop leaves s_root set, but\n  s_op still points at simple_super_operations, which has no\n  ->put_super(). bm_fill_super() installs s_ops only once\n  simple_fill_super() returned success, and installing it earlier\n  wouldn't help either because simple_fill_super() overwrites s_op.\n\nEither way vfs_get_super() calls deactivate_locked_super() and the\nreference is gone for good. binfmt_misc mounts are available in a user\nnamespace and both the inode and the dentry cache are SLAB_ACCOUNT, so\nan unprivileged caller under a tight memory cgroup can fail\nsimple_fill_super() on demand and leak one user namespace per attempt.\n\nDrop the reference in ->kill_sb() instead, which runs unconditionally,\nthe same way nfsd and rpc_pipefs release their keyed s_fs_info.\n\nThat also stops ->put_super() from clearing s_fs_info while the\nsuperblock is still on @fs_supers. generic_shutdown_super() leaves it\nthere on purpose so that sget_fc() keeps finding it until kill_sb() has\nrun, but a NULL s_fs_info makes test_keyed_super() miss it, so a\nconcurrent mount for the same user namespace skips the grab_super()\nwait and creates a second superblock for a namespace that is still\nbeing torn down.","publishedAt":"2026-08-15T12:27:15.709Z","updatedAt":"2026-08-23T12:47:24.496Z","severity":null,"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"21ca59b365c091d583f36ac753eaa8baf947be6f","status":"affected","lessThan":"ffec017158d3aad8a6ffca1dfad63d63bde9caad","versionType":"git"},{"version":"21ca59b365c091d583f36ac753eaa8baf947be6f","status":"affected","lessThan":"867aed6a4848761190d5ebdedf9642648f97bceb","versionType":"git"},{"version":"21ca59b365c091d583f36ac753eaa8baf947be6f","status":"affected","lessThan":"87a4eb9bbb3497f749bbac612af22ddaa62d7b0d","versionType":"git"},{"version":"21ca59b365c091d583f36ac753eaa8baf947be6f","status":"affected","lessThan":"b8206f516fe7cbe785cf44bf09c17c438d7c3cad","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/binfmt_misc.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.7","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.7","versionType":"semver"},{"version":"6.12.105","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.46","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.1.8","status":"unaffected","lessThanOrEqual":"7.1.*","versionType":"semver"},{"version":"7.2","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/binfmt_misc.c"]}],"references":["https://git.kernel.org/stable/c/ffec017158d3aad8a6ffca1dfad63d63bde9caad","https://git.kernel.org/stable/c/867aed6a4848761190d5ebdedf9642648f97bceb","https://git.kernel.org/stable/c/87a4eb9bbb3497f749bbac612af22ddaa62d7b0d","https://git.kernel.org/stable/c/b8206f516fe7cbe785cf44bf09c17c438d7c3cad"],"weaknesses":[],"ingestedAt":"2026-10-29T20:12:58.252Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/74xxx/CVE-2026-74483.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-74483","state":"PUBLISHED","datePublished":"2026-08-15T12:27:15.709Z","dateUpdated":"2026-08-23T12:47:24.496Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-08-15T05:44:03.904Z"},"containers":{"cna":{"title":"binfmt_misc: don't leak the user namespace when the mount fails","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nbinfmt_misc: don't leak the user namespace when the mount fails\n\nbm_get_tree() takes a reference to the user namespace and hands it to\nget_tree_keyed() as the sget key. sget_fc() moves that reference into\nsb->s_fs_info and clears fc->s_fs_info, so from that point on the\nsuperblock owns it and bm_free() doesn't see it anymore.\n\nThe superblock drops it in ->put_super(). But generic_shutdown_super()\nonly calls ->put_super() from inside the if (sb->s_root) branch, so\nnothing releases it when bm_fill_super() fails:\n\n- The kzalloc_obj() failure leaves s_root NULL and the whole branch is\n  skipped.\n\n- A simple_fill_super() failure in the file loop leaves s_root set, but\n  s_op still points at simple_super_operations, which has no\n  ->put_super(). bm_fill_super() installs s_ops only once\n  simple_fill_super() returned success, and installing it earlier\n  wouldn't help either because simple_fill_super() overwrites s_op.\n\nEither way vfs_get_super() calls deactivate_locked_super() and the\nreference is gone for good. binfmt_misc mounts are available in a user\nnamespace and both the inode and the dentry cache are SLAB_ACCOUNT, so\nan unprivileged caller under a tight memory cgroup can fail\nsimple_fill_super() on demand and leak one user namespace per attempt.\n\nDrop the reference in ->kill_sb() instead, which runs unconditionally,\nthe same way nfsd and rpc_pipefs release their keyed s_fs_info.\n\nThat also stops ->put_super() from clearing s_fs_info while the\nsuperblock is still on @fs_supers. generic_shutdown_super() leaves it\nthere on purpose so that sget_fc() keeps finding it until kill_sb() has\nrun, but a NULL s_fs_info makes test_keyed_super() miss it, so a\nconcurrent mount for the same user namespace skips the grab_super()\nwait and creates a second superblock for a namespace that is still\nbeing torn down."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"21ca59b365c091d583f36ac753eaa8baf947be6f","status":"affected","lessThan":"ffec017158d3aad8a6ffca1dfad63d63bde9caad","versionType":"git"},{"version":"21ca59b365c091d583f36ac753eaa8baf947be6f","status":"affected","lessThan":"867aed6a4848761190d5ebdedf9642648f97bceb","versionType":"git"},{"version":"21ca59b365c091d583f36ac753eaa8baf947be6f","status":"affected","lessThan":"87a4eb9bbb3497f749bbac612af22ddaa62d7b0d","versionType":"git"},{"version":"21ca59b365c091d583f36ac753eaa8baf947be6f","status":"affected","lessThan":"b8206f516fe7cbe785cf44bf09c17c438d7c3cad","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/binfmt_misc.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.7","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.7","versionType":"semver"},{"version":"6.12.105","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.46","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.1.8","status":"unaffected","lessThanOrEqual":"7.1.*","versionType":"semver"},{"version":"7.2","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/binfmt_misc.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/ffec017158d3aad8a6ffca1dfad63d63bde9caad"},{"url":"https://git.kernel.org/stable/c/867aed6a4848761190d5ebdedf9642648f97bceb"},{"url":"https://git.kernel.org/stable/c/87a4eb9bbb3497f749bbac612af22ddaa62d7b0d"},{"url":"https://git.kernel.org/stable/c/b8206f516fe7cbe785cf44bf09c17c438d7c3cad"}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-08-23T12:47:24.496Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.7","versionEndExcluding":"6.12.105"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.7","versionEndExcluding":"6.18.46"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.7","versionEndExcluding":"7.1.8"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.7","versionEndExcluding":"7.2"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}