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[192.26.29.3]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49cf755c22esm60770335e9.0.2026.09.04.03.42.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 04 Sep 2026 03:42:20 -0700 (PDT) From: Kumar Kartikeya Dwivedi To: bpf@vger.kernel.org Cc: Nuoqi Gui , Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , Eduard Zingerman , Emil Tsalapatis , Nicholas Carlini , kkd@meta.com, kernel-team@meta.com Subject: [PATCH bpf v1 4/8] selftests/bpf: Test rhtab kptr cancellation semantics Date: Fri, 4 Sep 2026 12:41:55 +0200 Message-ID: <20260904104203.345917-5-memxor@gmail.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260904104203.345917-1-memxor@gmail.com> References: <20260904104203.345917-1-memxor@gmail.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=4762; i=memxor@gmail.com; h=from:subject; bh=remhb3wJMtnH0GUA3NEWaFTCYTbotDIyClUmSy0fTuk=; b=owGbwMvMwCXmrmtenRyi38x4Wi2JIWvW/LNqGxKic886nDG2kg3o/qb0RumM/uq1eh/3R0fHS 2o+ClvXUcrCIMbFICumyFLyfx+T8YnK34G2y7hh5rAygQxh4OIUgInYrGD4735tmnf4986WxuUr HJY/ucfKfy2Y441aSOLE+RvMHp3eepKR4cOKFYzBkXxTJfpUDeY9fN70ZOOXPbGl/w6eYIlpOte WywMA X-Developer-Key: i=memxor@gmail.com; a=openpgp; fpr=B34BD741DE8494B76E2F717880EF20021D46C59B Content-Transfer-Encoding: 8bit From: Nuoqi Gui Resizable hash-map updates and deletions must not perform full special-field destruction in their caller context. In particular, a referenced kptr must remain attached to the allocation until the memory allocator destructor can release it safely. Add separate coverage for both affected paths. The update test stores a task kptr, replaces the ordinary value bytes with BPF_EXIST, and verifies that the kptr survived. The delete test removes an element and exchanges its kptr through the still-valid map-value pointer before the allocation is reclaimed. Both cases observe a NULL kptr when rhtab uses bpf_obj_free_fields(). They recover and release the reference after rhtab switches to cancellation semantics. Signed-off-by: Nuoqi Gui [ kkd: Split update and delete coverage and rewrote the commit log ] Signed-off-by: Kumar Kartikeya Dwivedi --- .../testing/selftests/bpf/prog_tests/rhash.c | 6 + tools/testing/selftests/bpf/progs/rhash.c | 112 ++++++++++++++++++ 2 files changed, 118 insertions(+) diff --git a/tools/testing/selftests/bpf/prog_tests/rhash.c b/tools/testing/selftests/bpf/prog_tests/rhash.c index 98bb66907b7f..0641bd5b0a9e 100644 --- a/tools/testing/selftests/bpf/prog_tests/rhash.c +++ b/tools/testing/selftests/bpf/prog_tests/rhash.c @@ -172,6 +172,12 @@ void test_rhash(void) if (test__start_subtest("test_rhash_delete_nonexistent")) rhash_run("test_rhash_delete_nonexistent"); + if (test__start_subtest("test_rhash_kptr_update")) + rhash_run("test_rhash_kptr_update"); + + if (test__start_subtest("test_rhash_kptr_delete")) + rhash_run("test_rhash_kptr_delete"); + if (test__start_subtest("test_rhash_map_extra_presize")) rhash_map_extra_presize(); diff --git a/tools/testing/selftests/bpf/progs/rhash.c b/tools/testing/selftests/bpf/progs/rhash.c index fc2dac3a719e..aea4de8dc781 100644 --- a/tools/testing/selftests/bpf/progs/rhash.c +++ b/tools/testing/selftests/bpf/progs/rhash.c @@ -19,6 +19,11 @@ struct elem { int val; }; +struct special_elem { + struct task_struct __kptr *task; + int val; +}; + struct { __uint(type, BPF_MAP_TYPE_RHASH); __uint(map_flags, BPF_F_NO_PREALLOC); @@ -27,6 +32,17 @@ struct { __type(value, struct elem); } rhmap SEC(".maps"); +struct { + __uint(type, BPF_MAP_TYPE_RHASH); + __uint(map_flags, BPF_F_NO_PREALLOC); + __uint(max_entries, 1); + __type(key, int); + __type(value, struct special_elem); +} special_fields SEC(".maps"); + +extern struct task_struct *bpf_task_acquire(struct task_struct *p) __ksym; +extern void bpf_task_release(struct task_struct *p) __ksym; + SEC("syscall") int test_rhash_lookup_update(void *ctx) { @@ -246,3 +262,99 @@ int test_rhash_delete_nonexistent(void *ctx) err = 0; return 0; } + +SEC("syscall") +int test_rhash_kptr_update(void *ctx) +{ + struct special_elem val1 = { .val = 1 }; + struct special_elem val2 = { .val = 2 }; + struct task_struct *task, *old; + struct special_elem *elem; + int key = 0; + + err = 1; + if (bpf_map_update_elem(&special_fields, &key, &val1, BPF_NOEXIST)) + return 1; + + err = 2; + elem = bpf_map_lookup_elem(&special_fields, &key); + if (!elem) + return 2; + + err = 3; + task = bpf_task_acquire(bpf_get_current_task_btf()); + if (!task) + return 3; + + err = 4; + old = bpf_kptr_xchg(&elem->task, task); + if (old) { + bpf_task_release(old); + return 4; + } + + err = 5; + if (bpf_map_update_elem(&special_fields, &key, &val2, BPF_EXIST)) + return 5; + + err = 6; + elem = bpf_map_lookup_elem(&special_fields, &key); + if (!elem || elem->val != 2) + return 6; + + err = 7; + old = bpf_kptr_xchg(&elem->task, NULL); + if (!old) + return 7; + bpf_task_release(old); + + err = 8; + if (bpf_map_delete_elem(&special_fields, &key)) + return 8; + + err = 0; + return 0; +} + +SEC("syscall") +int test_rhash_kptr_delete(void *ctx) +{ + struct special_elem val = {}; + struct task_struct *task, *old; + struct special_elem *elem; + int key = 0; + + err = 1; + if (bpf_map_update_elem(&special_fields, &key, &val, BPF_NOEXIST)) + return 1; + + err = 2; + elem = bpf_map_lookup_elem(&special_fields, &key); + if (!elem) + return 2; + + err = 3; + task = bpf_task_acquire(bpf_get_current_task_btf()); + if (!task) + return 3; + + err = 4; + old = bpf_kptr_xchg(&elem->task, task); + if (old) { + bpf_task_release(old); + return 4; + } + + err = 5; + if (bpf_map_delete_elem(&special_fields, &key)) + return 5; + + err = 6; + old = bpf_kptr_xchg(&elem->task, NULL); + if (!old) + return 6; + bpf_task_release(old); + + err = 0; + return 0; +} -- 2.53.0