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Message-ID: <2024082152-CVE-2024-43882-4fa4@gregkh> Date: Wed, 21 Aug 2024 08:10:53 +0800 From: Greg Kroah-Hartman <gregkh@...uxfoundation.org> To: linux-cve-announce@...r.kernel.org Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org> Subject: CVE-2024-43882: exec: Fix ToCToU between perm check and set-uid/gid usage Description =========== In the Linux kernel, the following vulnerability has been resolved: exec: Fix ToCToU between perm check and set-uid/gid usage When opening a file for exec via do_filp_open(), permission checking is done against the file's metadata at that moment, and on success, a file pointer is passed back. Much later in the execve() code path, the file metadata (specifically mode, uid, and gid) is used to determine if/how to set the uid and gid. However, those values may have changed since the permissions check, meaning the execution may gain unintended privileges. For example, if a file could change permissions from executable and not set-id: ---------x 1 root root 16048 Aug 7 13:16 target to set-id and non-executable: ---S------ 1 root root 16048 Aug 7 13:16 target it is possible to gain root privileges when execution should have been disallowed. While this race condition is rare in real-world scenarios, it has been observed (and proven exploitable) when package managers are updating the setuid bits of installed programs. Such files start with being world-executable but then are adjusted to be group-exec with a set-uid bit. For example, "chmod o-x,u+s target" makes "target" executable only by uid "root" and gid "cdrom", while also becoming setuid-root: -rwxr-xr-x 1 root cdrom 16048 Aug 7 13:16 target becomes: -rwsr-xr-- 1 root cdrom 16048 Aug 7 13:16 target But racing the chmod means users without group "cdrom" membership can get the permission to execute "target" just before the chmod, and when the chmod finishes, the exec reaches brpm_fill_uid(), and performs the setuid to root, violating the expressed authorization of "only cdrom group members can setuid to root". Re-check that we still have execute permissions in case the metadata has changed. It would be better to keep a copy from the perm-check time, but until we can do that refactoring, the least-bad option is to do a full inode_permission() call (under inode lock). It is understood that this is safe against dead-locks, but hardly optimal. The Linux kernel CVE team has assigned CVE-2024-43882 to this issue. Affected and fixed versions =========================== Fixed in 4.19.320 with commit d5c3c7e26275 Fixed in 5.4.282 with commit 368f6985d466 Fixed in 5.10.224 with commit 15469d46ba34 Fixed in 5.15.165 with commit 9b424c5d4130 Fixed in 6.1.106 with commit f6cfc6bcfd5e Fixed in 6.6.47 with commit d2a2a4714d80 Fixed in 6.10.6 with commit 90dfbba89ad4 Fixed in 6.11-rc4 with commit f50733b45d86 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-2024-43882 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/exec.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/d5c3c7e26275a2d83b894d30f7582a42853a958f https://git.kernel.org/stable/c/368f6985d46657b8b466a421dddcacd4051f7ada https://git.kernel.org/stable/c/15469d46ba34559bfe7e3de6659115778c624759 https://git.kernel.org/stable/c/9b424c5d4130d56312e2a3be17efb0928fec4d64 https://git.kernel.org/stable/c/f6cfc6bcfd5e1cf76115b6450516ea4c99897ae1 https://git.kernel.org/stable/c/d2a2a4714d80d09b0f8eb6438ab4224690b7121e https://git.kernel.org/stable/c/90dfbba89ad4f0d9c9744ecbb1adac4aa2ff4f3e https://git.kernel.org/stable/c/f50733b45d865f91db90919f8311e2127ce5a0cb
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