On 4/30/24 1:34 PM, Nicolas Bouchinet wrote:
> From: Nicolas Bouchinet <nicolas.bouchinet@xxxxxxxxxxx>
>
> 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
>
> Co-developed-by: Chengming Zhou <chengming.zhou@xxxxxxxxx>
Chengming Zhou, could you provide your s-o-b please?
> Signed-off-by: Nicolas Bouchinet <nicolas.bouchinet@xxxxxxxxxxx>
Added to slab/for-6.9-rc7/fixes, thanks!
