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Tue, 18 Aug 2026 20:30:57 -0700 (PDT) Received: from localhost.localdomain ([180.138.223.172]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3957fb17f48sm1016793a91.2.2026.08.18.20.30.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 18 Aug 2026 20:30:57 -0700 (PDT) From: nanx95726@gmail.com To: smfrench@gmail.com, linkinjeon@kernel.org, tom@talpey.com, senozhatsky@chromium.org, chenxiaosong@kylinos.cn Cc: linux-cifs@vger.kernel.org, Hang Nan Subject: [PATCH v4 2/3] ksmbd: test smb_check_perm_dacl() DACL walk boundary Date: Wed, 19 Aug 2026 11:30:12 +0800 Message-ID: <20260819033013.46824-3-nanx95726@gmail.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260819033013.46824-1-nanx95726@gmail.com> References: <20260819033013.46824-1-nanx95726@gmail.com> Precedence: bulk X-Mailing-List: linux-cifs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Hang Nan Drive smb_check_perm_dacl() through ksmbd's NTACL xattr path with a crafted descriptor whose second ACE is beyond the declared DACL size. Verify that the out-of-boundary ACE is not selected and access remains denied. Suggested-by: ChenXiaoSong Signed-off-by: Hang Nan Reviewed-by: ChenXiaoSong --- fs/smb/server/smbacl.c | 2 + fs/smb/server/tests/smbacl_kunit.c | 90 ++++++++++++++++++++++++++++++ fs/smb/server/vfs.c | 2 + 3 files changed, 94 insertions(+) diff --git a/fs/smb/server/smbacl.c b/fs/smb/server/smbacl.c index 8ad2e5a5cca8..5b2d46c09da7 100644 --- a/fs/smb/server/smbacl.c +++ b/fs/smb/server/smbacl.c @@ -7,6 +7,7 @@ */ #include +#include #include #include #include @@ -1652,6 +1653,7 @@ int smb_check_perm_dacl(struct ksmbd_conn *conn, const struct path *path, kfree(pntsd); return rc; } +EXPORT_SYMBOL_IF_KUNIT(smb_check_perm_dacl); int set_info_sec(struct ksmbd_conn *conn, struct ksmbd_tree_connect *tcon, const struct path *path, struct smb_ntsd *pntsd, int ntsd_len, diff --git a/fs/smb/server/tests/smbacl_kunit.c b/fs/smb/server/tests/smbacl_kunit.c index 733c2fa92030..391b1f5d181c 100644 --- a/fs/smb/server/tests/smbacl_kunit.c +++ b/fs/smb/server/tests/smbacl_kunit.c @@ -11,13 +11,22 @@ * security descriptor (the pre-fix behaviour) selects an ACE that * sits beyond struct smb_acl::size; stopping at the declared DACL * size (the fixed behaviour) rejects it. + * + * - ksmbd_smb_check_perm_dacl_boundary: drives the real + * smb_check_perm_dacl() with a descriptor stored through ksmbd's own + * NTACL xattr path on a tmpfs file, and asserts that a post-boundary + * ACE is not selected for a regular access check. */ #include +#include +#include +#include #include #include "../smbacl.h" #include "../smb_common.h" +#include "../vfs.h" struct ksmbd_acl_walk_result { bool found; @@ -154,8 +163,88 @@ static void ksmbd_dacl_walk_must_stop_at_declared_size(struct kunit *test) KUNIT_EXPECT_TRUE(test, enclosing.allowed); } +/* + * Build an NTSD whose DACL declares one ACE (pdacl->size) but actually + * contains two: the second ACE sits beyond the declared DACL boundary + * yet inside the enclosing security descriptor. The trailing ACE applies + * to S-1-22-1-0, which smb_check_perm_dacl() looks for when uid is zero. + */ +static struct smb_ntsd *build_boundary_ntsd(struct kunit *test, + const struct smb_sid *first_sid, + u32 first_access, + u32 trailing_access, + int *ntsd_size) +{ + struct smb_ntsd *pntsd; + struct smb_acl *pdacl; + struct smb_ace *ace; + u16 first_size = test_ace_size(first_sid); + u16 trailing_size = test_ace_size(&test_owner_sid); + + *ntsd_size = sizeof(struct smb_ntsd) + sizeof(struct smb_acl) + + first_size + trailing_size; + pntsd = kunit_kzalloc(test, *ntsd_size, GFP_KERNEL); + if (!pntsd) + return NULL; + + pntsd->revision = cpu_to_le16(SD_REVISION); + pntsd->type = cpu_to_le16(DACL_PRESENT); + pntsd->dacloffset = cpu_to_le32(sizeof(struct smb_ntsd)); + + pdacl = (struct smb_acl *)((char *)pntsd + sizeof(struct smb_ntsd)); + pdacl->revision = cpu_to_le16(2); + pdacl->num_aces = cpu_to_le16(2); + pdacl->size = cpu_to_le16(sizeof(struct smb_acl) + first_size); + + ace = (struct smb_ace *)((char *)pdacl + sizeof(struct smb_acl)); + fill_test_ace(ace, first_sid, first_access); + + ace = (struct smb_ace *)((char *)ace + first_size); + fill_test_ace(ace, &test_owner_sid, trailing_access); + + return pntsd; +} + +static void ksmbd_smb_check_perm_dacl_boundary_test(struct kunit *test) +{ + struct file *file; + struct smb_ntsd *pntsd; + __le32 daccess = cpu_to_le32(FILE_READ_DATA); + int ntsd_size, rc; + + pntsd = build_boundary_ntsd(test, &test_nonmatching_sid, 0, + FILE_READ_DATA, &ntsd_size); + KUNIT_ASSERT_NOT_NULL(test, pntsd); + + file = shmem_file_setup("ksmbd-kunit-dacl", 0, + mk_vma_flags(VMA_NORESERVE_BIT)); + KUNIT_ASSERT_NOT_ERR_OR_NULL(test, file); + + rc = ksmbd_vfs_set_sd_xattr(NULL, mnt_idmap(file->f_path.mnt), + &file->f_path, pntsd, ntsd_size, + false); + KUNIT_EXPECT_EQ(test, 0, rc); + if (rc) + goto out; + + rc = smb_check_perm_dacl(NULL, &file->f_path, &daccess, + cpu_to_le32(FILE_READ_DATA), 0, false); + + /* + * The post-boundary ACE (ACE #2, beyond pdacl->size) grants + * FILE_READ_DATA to the caller's SID, but it must not be + * selected: the walk stops at the declared DACL size and access + * is denied. Before the fix the walk used the enclosing + * descriptor length, selected ACE #2 and returned 0. + */ + KUNIT_EXPECT_EQ(test, -EACCES, rc); +out: + fput(file); +} + static struct kunit_case ksmbd_smbacl_test_cases[] = { KUNIT_CASE(ksmbd_dacl_walk_must_stop_at_declared_size), + KUNIT_CASE(ksmbd_smb_check_perm_dacl_boundary_test), {} }; @@ -168,3 +257,4 @@ kunit_test_suite(ksmbd_smbacl_test_suite); MODULE_DESCRIPTION("KUnit tests for ksmbd smbacl helpers"); MODULE_LICENSE("GPL"); +MODULE_IMPORT_NS("EXPORTED_FOR_KUNIT_TESTING"); diff --git a/fs/smb/server/vfs.c b/fs/smb/server/vfs.c index 286536f75144..536300f9eb8f 100644 --- a/fs/smb/server/vfs.c +++ b/fs/smb/server/vfs.c @@ -5,6 +5,7 @@ */ #include +#include #include #include #include @@ -1668,6 +1669,7 @@ int ksmbd_vfs_set_sd_xattr(struct ksmbd_conn *conn, kfree(def_smb_acl); return rc; } +EXPORT_SYMBOL_IF_KUNIT(ksmbd_vfs_set_sd_xattr); int ksmbd_vfs_get_sd_xattr(struct ksmbd_conn *conn, struct mnt_idmap *idmap, -- 2.55.0