AI Score
Confidence
Low
EPSS
Percentile
9.0%
SSVC
Exploitation
none
Automatable
no
Technical Impact
partial
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
[
{
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"product": "Linux",
"versions": [
{
"status": "affected",
"version": "284f17ac13fe",
"lessThan": "56900355485f",
"versionType": "git"
},
{
"status": "affected",
"version": "284f17ac13fe",
"lessThan": "8f828aa48812",
"versionType": "git"
}
],
"programFiles": [
"mm/slub.c"
],
"defaultStatus": "unaffected"
},
{
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"product": "Linux",
"versions": [
{
"status": "affected",
"version": "6.8"
},
{
"status": "unaffected",
"version": "0",
"lessThan": "6.8",
"versionType": "custom"
},
{
"status": "unaffected",
"version": "6.8.10",
"versionType": "custom",
"lessThanOrEqual": "6.8.*"
},
{
"status": "unaffected",
"version": "6.9",
"versionType": "original_commit_for_fix",
"lessThanOrEqual": "*"
}
],
"programFiles": [
"mm/slub.c"
],
"defaultStatus": "affected"
}
]