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([117.133.183.252]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-84f5a5528adsm797510b3a.45.2026.08.07.03.12.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 07 Aug 2026 03:12:26 -0700 (PDT) From: Baineng Shou To: Sumit Semwal , =?UTF-8?q?Christian=20K=C3=B6nig?= , "T . J . Mercier" , Benjamin Gaignard , Brian Starkey , John Stultz , Sandeep Patil , "Andrew F . Davis" , Srinivas Kandagatla , David Airlie , Simona Vetter Cc: stable@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-media@vger.kernel.org, linaro-mm-sig@lists.linaro.org, linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org, Baineng Shou Subject: [PATCH v6 4/4] selftests: dmabuf-heaps: add fd-leak-on-EFAULT regression test Date: Fri, 7 Aug 2026 18:11:40 +0800 Message-Id: <20260807101140.1357218-5-shoubaineng@gmail.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20260807101140.1357218-1-shoubaineng@gmail.com> References: <20260807101140.1357218-1-shoubaineng@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Add a test case that verifies no file descriptor is leaked when DMA_HEAP_IOCTL_ALLOC succeeds internally but copy_to_user() fails to deliver the fd number back to userspace. The failure is triggered by placing the ioctl argument in a private anonymous page and flipping it to PROT_READ (via mprotect) between the kernel's copy_from_user() and copy_to_user() calls. With the buggy kernel the ioctl returns -EFAULT but leaves an extra open fd in the process's fd table; with the fixed kernel the fd count is unchanged. This serves as a regression test for: "dma-buf: dma-heap: don't publish fd before copy_to_user() succeeds" Suggested-by: Sumit Semwal Signed-off-by: Baineng Shou --- .../selftests/dmabuf-heaps/dmabuf-heap.c | 113 +++++++++++++++++- 1 file changed, 112 insertions(+), 1 deletion(-) diff --git a/tools/testing/selftests/dmabuf-heaps/dmabuf-heap.c b/tools/testing/selftests/dmabuf-heaps/dmabuf-heap.c index fc9694fc4e89..1d49df671919 100644 --- a/tools/testing/selftests/dmabuf-heaps/dmabuf-heap.c +++ b/tools/testing/selftests/dmabuf-heaps/dmabuf-heap.c @@ -390,6 +390,116 @@ static void test_alloc_errors(char *heap_name) close(heap_fd); } +/* + * count_open_fds - return the number of open file descriptors. + * + * The fd opened by opendir() itself is counted, but since it is opened + * and closed within each call, it cancels out when comparing two counts. + * Returns -1 on error. + */ +static int count_open_fds(void) +{ + DIR *d = opendir("/proc/self/fd"); + struct dirent *de; + int count = 0; + + if (!d) + return -1; + + while ((de = readdir(d))) + if (de->d_name[0] != '.') + count++; + closedir(d); + return count; +} + +/* + * test_alloc_no_fd_leak_on_efault - verify no fd is leaked when + * copy_to_user() fails during DMA_HEAP_IOCTL_ALLOC. + * + * The bug: dma_buf_fd() called fd_install() before copy_to_user(). + * If copy_to_user() then failed (e.g. via mprotect), the fd was + * silently installed in the fd table but never returned to userspace. + * + * The fix: reserve the fd with get_unused_fd_flags() first, attempt + * copy_to_user(), and only call fd_install() on success. + * + * We trigger the failure by placing the ioctl argument in a private + * anonymous page and flipping it to PROT_READ before the ioctl. + * Inside the kernel, copy_from_user() reads from the page (reads are + * allowed under PROT_READ, so it succeeds), but copy_to_user() that + * writes the fd number back faults, returning -EFAULT. We then + * count open file descriptors before and after; with the bug an extra + * fd is left in the table. + */ +static void test_alloc_no_fd_leak_on_efault(char *heap_name) +{ + int heap_fd = -1; + int fd_before, fd_after; + int ret; + long page_size; + struct dma_heap_allocation_data *req; + + ksft_print_msg("Testing fd leak when copy_to_user() fails:\n"); + + heap_fd = dmabuf_heap_open(heap_name); + + page_size = sysconf(_SC_PAGESIZE); + + /* + * Place the ioctl argument in its own private anonymous page so + * we can flip its protection independently. + */ + req = mmap(NULL, page_size, PROT_READ | PROT_WRITE, + MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); + if (req == MAP_FAILED) { + ksft_test_result_fail("mmap failed: %s\n", strerror(errno)); + goto out; + } + + memset(req, 0, sizeof(*req)); + req->len = page_size; + req->fd_flags = O_RDWR | O_CLOEXEC; + + fd_before = count_open_fds(); + if (fd_before < 0) { + ksft_test_result_fail("count_open_fds: %s\n", strerror(errno)); + munmap(req, page_size); + goto out; + } + + /* + * Make the page read-only so copy_to_user() will fault. The + * ioctl must fail with -1; if it returns success the test setup + * is broken (mprotect is synchronous, so there is no race). + */ + mprotect(req, page_size, PROT_READ); + + ret = ioctl(heap_fd, DMA_HEAP_IOCTL_ALLOC, req); + + /* Re-allow writes so munmap can clean up */ + mprotect(req, page_size, PROT_READ | PROT_WRITE); + munmap(req, page_size); + + if (ret != -1) { + ksft_test_result_fail("ioctl returned %d, expected -1 EFAULT\n", + ret); + goto out; + } + + fd_after = count_open_fds(); + if (fd_after < 0) { + ksft_test_result_fail("count_open_fds: %s\n", strerror(errno)); + goto out; + } + + ksft_test_result(fd_before == fd_after, + "fd leak on EFAULT: before=%d after=%d\n", + fd_before, fd_after); +out: + close(heap_fd); +} + static int numer_of_heaps(void) { DIR *d = opendir(DEVPATH); @@ -420,7 +530,7 @@ int main(void) return KSFT_SKIP; } - ksft_set_plan(11 * numer_of_heaps()); + ksft_set_plan(12 * numer_of_heaps()); while ((dir = readdir(d))) { if (!strncmp(dir->d_name, ".", 2)) @@ -435,6 +545,7 @@ int main(void) test_alloc_zeroed(dir->d_name, ONE_MEG); test_alloc_compat(dir->d_name); test_alloc_errors(dir->d_name); + test_alloc_no_fd_leak_on_efault(dir->d_name); } closedir(d); -- 2.34.1