From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 016AE3B5319; Sat, 17 Oct 2026 17:21:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792257716; cv=none; b=j7ks+/gRcIUAG7pjK3xTHVvdogTS5QDXSxF+Ax3pc62Uvmm6nq5KI4P68g9Pf+zFUJ3WGhD2nierG7jqq7VH6oZjnybXN8HKBtNdRwAeeC2lUqgYVnwvi+jalg0hIAfM++K/0uR5qmc6CLDQUZOUHeb1EtoWqB5aMeROc+E1gjo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792257716; c=relaxed/simple; bh=EH2zQ+Nd7oveNI0hTugQiwZbOGvRDMSgVUh/mblG7WI=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=GuPhnpNdBpghzd8fMhyBGNYE2COF71S8SrAcCEO57efiWKPG+9Qy50QoREw82pv8TRUP5yv5cQmMrW4j1V1MoaOIuxHVT7XMo6gBnFPTa3IotP54wO3GuHi+vA+md/Lux80N8szr+4uhWbdl/RQdBpW4kvNYXv9M3JFqpFXfhac= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=pU6HBRa9; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="pU6HBRa9" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2B0D61F000C5; Sat, 17 Oct 2026 17:21:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1792257714; bh=lAI0+f+hjD8aoxFVovPYoySlInuCKU/yEy4szEqQ1W8=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=pU6HBRa9MS0mlMQnS4oz0pwZHsiqhRBy7Af8glsT98MZqAd41ltcIFtmA4k0O9JA6 ddGiMB76mHzff3cOAazMDcx7391A16WSLFPdJGqFze3JQp4w7NQyeftZzyidDZperk TOPS6TrQc1VjgPla8Ig84JGIxQTCBJZOMeDMvN7E= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Chengming Zhou , Nicolas Bouchinet , Vlastimil Babka , Sasha Levin Subject: [PATCH 6.6 0646/1674] mm/slub: avoid zeroing outside-object freepointer for single free Date: Sat, 17 Oct 2026 17:48:38 +0200 Message-ID: <20261017160447.687610550@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261017160431.119607952@linuxfoundation.org> References: <20261017160431.119607952@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Nicolas Bouchinet [ Upstream commit 8f828aa48812ced28aa39cb3cfe55ef2444d03dd ] 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 Fixes: 284f17ac13fe ("mm/slub: handle bulk and single object freeing separately") Cc: Co-developed-by: Chengming Zhou Signed-off-by: Chengming Zhou Signed-off-by: Nicolas Bouchinet Signed-off-by: Vlastimil Babka Stable-dep-of: 59090e479ac7 ("mm, slub: avoid zeroing kmalloc redzone") Signed-off-by: Sasha Levin --- mm/slub.c | 52 +++++++++++++++++++++++++++++----------------------- 1 file changed, 29 insertions(+), 23 deletions(-) diff --git a/mm/slub.c b/mm/slub.c index c27bf00f3f275..9870dd4238ddc 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -452,6 +452,26 @@ static inline void set_freepointer(struct kmem_cache *s, void *object, void *fp) *(freeptr_t *)freeptr_addr = freelist_ptr_encode(s, fp, freeptr_addr); } +/* + * See comment in calculate_sizes(). + */ +static inline bool freeptr_outside_object(struct kmem_cache *s) +{ + return s->offset >= s->inuse; +} + +/* + * Return offset of the end of info block which is inuse + free pointer if + * not overlapping with object. + */ +static inline unsigned int get_info_end(struct kmem_cache *s) +{ + if (freeptr_outside_object(s)) + return s->inuse + sizeof(void *); + else + return s->inuse; +} + /* Loop over all objects in a slab */ #define for_each_object(__p, __s, __addr, __objects) \ for (__p = fixup_red_left(__s, __addr); \ @@ -740,26 +760,6 @@ static void print_section(char *level, char *text, u8 *addr, metadata_access_disable(); } -/* - * See comment in calculate_sizes(). - */ -static inline bool freeptr_outside_object(struct kmem_cache *s) -{ - return s->offset >= s->inuse; -} - -/* - * Return offset of the end of info block which is inuse + free pointer if - * not overlapping with object. - */ -static inline unsigned int get_info_end(struct kmem_cache *s) -{ - if (freeptr_outside_object(s)) - return s->inuse + sizeof(void *); - else - return s->inuse; -} - static struct track *get_track(struct kmem_cache *s, void *object, enum track_item alloc) { @@ -1808,15 +1808,20 @@ static __always_inline bool slab_free_hook(struct kmem_cache *s, * * The initialization memset's clear the object and the metadata, * but don't touch the SLAB redzone. + * + * The object's freepointer is also avoided if stored outside the + * object. */ if (init) { int rsize; + unsigned int inuse; + inuse = get_info_end(s); if (!kasan_has_integrated_init()) memset(kasan_reset_tag(x), 0, s->object_size); rsize = (s->flags & SLAB_RED_ZONE) ? s->red_left_pad : 0; - memset((char *)kasan_reset_tag(x) + s->inuse, 0, - s->size - s->inuse - rsize); + memset((char *)kasan_reset_tag(x) + inuse, 0, + s->size - inuse - rsize); } /* KASAN might put x into memory quarantine, delaying its reuse. */ return kasan_slab_free(s, x, init); @@ -3463,7 +3468,8 @@ static void *__slab_alloc_node(struct kmem_cache *s, static __always_inline void maybe_wipe_obj_freeptr(struct kmem_cache *s, void *obj) { - if (unlikely(slab_want_init_on_free(s)) && obj) + if (unlikely(slab_want_init_on_free(s)) && obj && + !freeptr_outside_object(s)) memset((void *)((char *)kasan_reset_tag(obj) + s->offset), 0, sizeof(void *)); } -- 2.53.0