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Mon, 15 Sep 2025 13:55:10 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id 6FZZHL4ayGhnVgAAD6G6ig (envelope-from ); Mon, 15 Sep 2025 13:55:10 +0000 From: Vlastimil Babka Date: Mon, 15 Sep 2025 15:55:12 +0200 Subject: [PATCH v2 5/6] slab: validate slab before using it in alloc_single_from_partial() Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20250915-slub-slab-validation-v2-5-314690fc1532@suse.cz> References: <20250915-slub-slab-validation-v2-0-314690fc1532@suse.cz> In-Reply-To: <20250915-slub-slab-validation-v2-0-314690fc1532@suse.cz> To: "Matthew Wilcox (Oracle)" Cc: Harry Yoo , Christoph Lameter , David Rientjes , Roman Gushchin , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Vlastimil Babka X-Mailer: b4 0.14.2 X-Spamd-Result: default: False [-4.30 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-0.997]; MIME_GOOD(-0.10)[text/plain]; RCVD_VIA_SMTP_AUTH(0.00)[]; ARC_NA(0.00)[]; RCVD_TLS_ALL(0.00)[]; MIME_TRACE(0.00)[0:+]; FUZZY_RATELIMITED(0.00)[rspamd.com]; TO_DN_SOME(0.00)[]; RCPT_COUNT_SEVEN(0.00)[9]; MID_RHS_MATCH_FROM(0.00)[]; DKIM_SIGNED(0.00)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; FROM_HAS_DN(0.00)[]; R_RATELIMIT(0.00)[to_ip_from(RLwn5r54y1cp81no5tmbbew5oc)]; FROM_EQ_ENVFROM(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo] X-Spam-Flag: NO X-Spam-Level: X-Spam-Score: -4.30 We touch slab->freelist and slab->inuse before checking the slab pointer is actually sane. Do that validation first, which will be safer. We can thus also remove the check from alloc_debug_processing(). This adds a new "s->flags & SLAB_CONSISTENCY_CHECKS" test but alloc_single_from_partial() is only called for caches with debugging enabled so it's acceptable. In alloc_single_from_new_slab() we just created the struct slab and call alloc_debug_processing() to mainly set up redzones, tracking etc, while not really expecting the consistency checks to fail. Thus don't validate it there. Signed-off-by: Vlastimil Babka Reviewed-by: Harry Yoo --- mm/slub.c | 20 ++++++++++++-------- 1 file changed, 12 insertions(+), 8 deletions(-) diff --git a/mm/slub.c b/mm/slub.c index 12ad42f3d2e066b02340f2c30a85422583af3c5d..e5b53d1debddd3fe0f941f579a1= 043a5b976e50b 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -821,6 +821,8 @@ static inline unsigned int get_orig_size(struct kmem_ca= che *s, void *object) return *(unsigned int *)p; } =20 +#ifdef CONFIG_SLUB_DEBUG + /* * For debugging context when we want to check if the struct slab pointer * appears to be valid. @@ -830,7 +832,6 @@ static inline bool validate_slab_ptr(struct slab *slab) return PageSlab(slab_page(slab)); } =20 -#ifdef CONFIG_SLUB_DEBUG static unsigned long object_map[BITS_TO_LONGS(MAX_OBJS_PER_PAGE)]; static DEFINE_SPINLOCK(object_map_lock); =20 @@ -1651,11 +1652,6 @@ static noinline bool alloc_debug_processing(struct k= mem_cache *s, struct slab *slab, void *object, int orig_size) { if (s->flags & SLAB_CONSISTENCY_CHECKS) { - if (!validate_slab_ptr(slab)) { - slab_err(s, slab, "Not a valid slab page"); - return false; - } - if (!alloc_consistency_checks(s, slab, object)) goto bad; } @@ -2825,13 +2821,21 @@ static void *alloc_single_from_partial(struct kmem_= cache *s, =20 lockdep_assert_held(&n->list_lock); =20 +#ifdef SLUB_DEBUG + if (s->flags & SLAB_CONSISTENCY_CHECKS) { + if (!validate_slab_ptr(slab)) { + slab_err(s, slab, "Not a valid slab page"); + return NULL; + } + } +#endif + object =3D slab->freelist; slab->freelist =3D get_freepointer(s, object); slab->inuse++; =20 if (!alloc_debug_processing(s, slab, object, orig_size)) { - if (validate_slab_ptr(slab)) - remove_partial(n, slab); + remove_partial(n, slab); return NULL; } =20 --=20 2.51.0