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wxR0AhrKyazcS7viLFJiFL5FHmnGwFjnAKRKGy7Sc2wKJCNS7wohybjOcwcC5aEwrGfl3XRhwRPvfACHmrL56F0ZYj8TFm7GotL2PaztGedSHzmYARcs+BwhDcHFA35imgZLhLiDRCRa93oGdcKN1Jx4CsrE0EfFSsfc4irjwPCvst8crI8bRF/J+mM28HvFvOmrIwak+Unbcye0bFGR1F6+NjcoKamA1KfX0oHR4sB+FAVJQ6ckqrkddkVYuLeOvZISoudHUmbmLSkJFffQEp/uiUGr+VeH0vxqgv0/Ae2lxNc+UVqk+BoIoShWrd0HW2euTeSSbJjpvt83A6sy29yVrl9zLhvR99DDjnrg/vgd4rfnawUV5PqI+PEwjdT+tdzEFSnkMiItLb0O/kFlsODDMYrgeSWj8fVONvG+qJwGkhB3JdzYm1tWegS85cynrGvBw17LPes2rczRbOAf/J1fiwngSPx1ReO/wa1hEXVlf95hqPsR8qbsMqLZ9ZK6QWj2IYjdNjKVH4Ibdc2oYkKxiKCF345GPdqMD+FJLmBbBWAhVUFwZxW+wx5sjSbEgMKaREtn7phBi1i0gJMfTP+JIeiXb+01Winci X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Aug 28, 2024 at 06:53:11PM +0200, Vlastimil Babka wrote: > On 8/25/24 15:05, Feng Tang wrote: > > On Fri, Aug 23, 2024 at 02:24:15PM +0800, Peng Fan (OSS) wrote: > >> From: Peng Fan > >> > >> With commit 946fa0dbf2d8 > >> ("mm/slub: extend redzone check to extra allocated kmalloc space than requested"), > >> setting orig_size treats the wasted space (object_size - orig_size) as > >> redzones. But (in check_object()) when orig_size is set to zero, the entire > >> object is perceived as a redzone. To a valid allocated kmalloc space, > >> when init_on_free=1, the wasted space and the orig_size should > >> not be cleared to 0, otherwise there will be kernel dump: > > Could we make it more clear? > > Since commit 946fa0dbf2d8 ("mm/slub: extend redzone check to extra allocated > kmalloc space than requested"), setting orig_size treats the wasted space > (object_size - orig_size) as a redzone. However with init_on_free=1 we clear > the full object->size, including the redzone. > > Additionally we clear the object metadata, including the stored orig_size, > making it zero, which makes check_object() treat the the whole object as a > redzone. > > These issues lead to the following BUG report with "slub_debug=FUZ > init_on_free=1": > > >> > >> [ 0.000000] ============================================================================= > >> [ 0.000000] BUG kmalloc-8 (Not tainted): kmalloc Redzone overwritten > >> [ 0.000000] ----------------------------------------------------------------------------- > >> [ 0.000000] > >> [ 0.000000] 0xffff000010032858-0xffff00001003285f @offset=2136. First byte 0x0 instead of 0xcc > >> [ 0.000000] FIX kmalloc-8: Restoring kmalloc Redzone 0xffff000010032858-0xffff00001003285f=0xcc > >> [ 0.000000] Slab 0xfffffdffc0400c80 objects=36 used=23 fp=0xffff000010032a18 flags=0x3fffe0000000200(workingset|node=0|zone=0|lastcpupid=0x1ffff) > >> [ 0.000000] Object 0xffff000010032858 @offset=2136 fp=0xffff0000100328c8 > >> [ 0.000000] > >> [ 0.000000] Redzone ffff000010032850: cc cc cc cc cc cc cc cc ........ > >> [ 0.000000] Object ffff000010032858: cc cc cc cc cc cc cc cc ........ > >> [ 0.000000] Redzone ffff000010032860: cc cc cc cc cc cc cc cc ........ > >> [ 0.000000] Padding ffff0000100328b4: 00 00 00 00 00 00 00 00 00 00 00 00 ............ > >> [ 0.000000] CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Not tainted 6.11.0-rc3-next-20240814-00004-g61844c55c3f4 #144 > >> [ 0.000000] Hardware name: NXP i.MX95 19X19 board (DT) > >> [ 0.000000] Call trace: > >> [ 0.000000] dump_backtrace+0x90/0xe8 > >> [ 0.000000] show_stack+0x18/0x24 > >> [ 0.000000] dump_stack_lvl+0x74/0x8c > >> [ 0.000000] dump_stack+0x18/0x24 > >> [ 0.000000] print_trailer+0x150/0x218 > >> [ 0.000000] check_object+0xe4/0x454 > >> [ 0.000000] free_to_partial_list+0x2f8/0x5ec > >> > >> To address the issue, use orig_size to clear the used area. And restore > >> the value of orig_size after clear the remaining area. > >> > >> When CONFIG_SLUB_DEBUG not defined, (get_orig_size()' directly returns > >> s->object_size. So when using memset to init the area, the size can simply > >> be orig_size, as orig_size returns object_size when CONFIG_SLUB_DEBUG not > >> enabled. And orig_size can never be bigger than object_size. > >> > >> Fixes: 946fa0dbf2d8 ("mm/slub: extend redzone check to extra allocated kmalloc space than requested") > > > > Thanks for the fix! I missed to test the 'init_on_free' case back then. > > > > Reviewed-by: Feng Tang > > By the way Feng, have you noticed the other issue we have, with krealloc() > and redzoning? Want to look at that? Thanks. > > https://lore.kernel.org/all/44fa564b-9c8f-4ac2-bce3-f6d2c99b73b7@suse.cz/ Sure. Will check that thread (it might take a while as I just came back from vacation). thanks - Feng