| From bippy-5f407fcff5a0 Mon Sep 17 00:00:00 2001 |
| From: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| To: <linux-cve-announce@vger.kernel.org> |
| Reply-to: <cve@kernel.org>, <linux-kernel@vger.kernel.org> |
| Subject: CVE-2024-36892: mm/slub: avoid zeroing outside-object freepointer for single free |
| |
| Description |
| =========== |
| |
| In the Linux kernel, the following vulnerability has been resolved: |
| |
| mm/slub: avoid zeroing outside-object freepointer for single free |
| |
| Commit 284f17ac13fe ("mm/slub: handle bulk and single object freeing |
| separately") splits single and bulk object freeing in two functions |
| slab_free() and slab_free_bulk() which leads slab_free() to call |
| slab_free_hook() directly instead of slab_free_freelist_hook(). |
| |
| If `init_on_free` is set, slab_free_hook() zeroes the object. |
| Afterward, if `slub_debug=F` and `CONFIG_SLAB_FREELIST_HARDENED` are |
| set, the do_slab_free() slowpath executes freelist consistency |
| checks and try to decode a zeroed freepointer which leads to a |
| "Freepointer corrupt" detection in check_object(). |
| |
| During bulk free, slab_free_freelist_hook() isn't affected as it always |
| sets it objects freepointer using set_freepointer() to maintain its |
| reconstructed freelist after `init_on_free`. |
| |
| For single free, object's freepointer thus needs to be avoided when |
| stored outside the object if `init_on_free` is set. The freepointer left |
| as is, check_object() may later detect an invalid pointer value due to |
| objects overflow. |
| |
| To reproduce, set `slub_debug=FU init_on_free=1 log_level=7` on the |
| command line of a kernel build with `CONFIG_SLAB_FREELIST_HARDENED=y`. |
| |
| dmesg sample log: |
| [ 10.708715] ============================================================================= |
| [ 10.710323] BUG kmalloc-rnd-05-32 (Tainted: G B T ): Freepointer corrupt |
| [ 10.712695] ----------------------------------------------------------------------------- |
| [ 10.712695] |
| [ 10.712695] Slab 0xffffd8bdc400d580 objects=32 used=4 fp=0xffff9d9a80356f80 flags=0x200000000000a00(workingset|slab|node=0|zone=2) |
| [ 10.716698] Object 0xffff9d9a80356600 @offset=1536 fp=0x7ee4f480ce0ecd7c |
| [ 10.716698] |
| [ 10.716698] Bytes b4 ffff9d9a803565f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ |
| [ 10.720703] Object ffff9d9a80356600: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ |
| [ 10.720703] Object ffff9d9a80356610: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ |
| [ 10.724696] Padding ffff9d9a8035666c: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ |
| [ 10.724696] Padding ffff9d9a8035667c: 00 00 00 00 .... |
| [ 10.724696] FIX kmalloc-rnd-05-32: Object at 0xffff9d9a80356600 not freed |
| |
| The Linux kernel CVE team has assigned CVE-2024-36892 to this issue. |
| |
| |
| Affected and fixed versions |
| =========================== |
| |
| Issue introduced in 6.8 with commit 284f17ac13fe34ae9eecbe57bb91553374d9b855 and fixed in 6.8.10 with commit 56900355485f6e82114b18c812edd57fd7970dcb |
| Issue introduced in 6.8 with commit 284f17ac13fe34ae9eecbe57bb91553374d9b855 and fixed in 6.9 with commit 8f828aa48812ced28aa39cb3cfe55ef2444d03dd |
| |
| 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-2024-36892 |
| 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: |
| mm/slub.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/56900355485f6e82114b18c812edd57fd7970dcb |
| https://git.kernel.org/stable/c/8f828aa48812ced28aa39cb3cfe55ef2444d03dd |
