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PUBLISHED

CVE-2024-36892

mm/slub: avoid zeroing outside-object freepointer for single free

Assigner:Linux (416baaa9-dc9f-4396-8d5f-8c081fb06d67)
Reserved:2024-05-30
Published:2024-05-30
Updated:2024-06-10

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

Product status

Default status
unaffected

284f17ac13fe before 56900355485f
affected

284f17ac13fe before 8f828aa48812
affected

Default status
affected

6.8
affected

Any version before 6.8
unaffected

6.8.10
unaffected

6.9
unaffected

References

https://git.kernel.org/stable/c/56900355485f6e82114b18c812edd57fd7970dcb

https://git.kernel.org/stable/c/8f828aa48812ced28aa39cb3cfe55ef2444d03dd

cve.org CVE-2024-36892

nvd.nist.gov CVE-2024-36892

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