The lsm_get_self_attr() syscall allows callers to pass in a NULL context buffer to find out the size of the output needed. That path still compared the computed entry size against the caller provided size first, so a NULL buffer with size 0 incorrectly returned -E2BIG rather than reporting the required size. Only enforce the available buffer length after checking for the NULL buffer. Cover the zero length sizing query in the self test. Fixes: d7cf3412a9f6 ("lsm: consolidate buffer size handling into lsm_fill_user_ctx()") Cc: stable@vger.kernel.org Signed-off-by: Bradley Morgan --- security/security.c | 8 ++++---- tools/testing/selftests/lsm/lsm_get_self_attr_test.c | 5 ++--- 2 files changed, 6 insertions(+), 7 deletions(-) diff --git a/security/security.c b/security/security.c index 71aea8fdf014..fa0d7e036249 100644 --- a/security/security.c +++ b/security/security.c @@ -406,15 +406,15 @@ int lsm_fill_user_ctx(struct lsm_ctx __user *uctx, u32 *uctx_len, int rc = 0; nctx_len = ALIGN(struct_size(nctx, ctx, val_len), sizeof(void *)); + /* no buffer - return success/0 and set @uctx_len to the req size */ + if (!uctx) + goto out; + if (nctx_len > *uctx_len) { rc = -E2BIG; goto out; } - /* no buffer - return success/0 and set @uctx_len to the req size */ - if (!uctx) - goto out; - nctx = kzalloc(nctx_len, GFP_KERNEL); if (nctx == NULL) { rc = -ENOMEM; diff --git a/tools/testing/selftests/lsm/lsm_get_self_attr_test.c b/tools/testing/selftests/lsm/lsm_get_self_attr_test.c index 60caf8528f81..2f5ababc2b95 100644 --- a/tools/testing/selftests/lsm/lsm_get_self_attr_test.c +++ b/tools/testing/selftests/lsm/lsm_get_self_attr_test.c @@ -39,15 +39,14 @@ TEST(size_null_lsm_get_self_attr) TEST(ctx_null_lsm_get_self_attr) { - const long page_size = sysconf(_SC_PAGESIZE); - __u32 size = page_size; + __u32 size = 0; int rc; rc = lsm_get_self_attr(LSM_ATTR_CURRENT, NULL, &size, 0); if (attr_lsm_count()) { ASSERT_NE(-1, rc); - ASSERT_NE(1, size); + ASSERT_NE(0, size); } else { ASSERT_EQ(-1, rc); } -- 2.53.0