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The test is a self-contained raw /dev/fuse server (no libfuse dependency) that runs without writeback_cache and returns FOPEN_KEEP_CACHE, the configuration in which the bug is visible. Its backing data is always zero in the hole, so any non-zero byte a read sees is stale page-cache data. All offsets are relative to the runtime page size. Four cases: - write_extend: pollute the post-EOF tail, extend past it by writing into a later page, and verify the tail reads back as zero; - ftruncate_extend: same, but extend via ftruncate(); - fallocate_extend: same, but extend via fallocate() at the old EOF; - extend_into_eof_page_preserves_data: an extending write landing inside the old EOF page must not be clobbered by the zeroing. Each case fails without the fix and passes with it. Signed-off-by: Jimmy Zuber --- .../selftests/filesystems/fuse/.gitignore | 1 + .../selftests/filesystems/fuse/Makefile | 3 + .../filesystems/fuse/write_extend_eof_test.c | 368 ++++++++++++++++++ 3 files changed, 372 insertions(+) create mode 100644 tools/testing/selftests/filesystems/fuse/write_extend_eof_test.c diff --git a/tools/testing/selftests/filesystems/fuse/.gitignore b/tools/testing/selftests/filesystems/fuse/.gitignore index 3e72e742d08e..fb51603fe419 100644 --- a/tools/testing/selftests/filesystems/fuse/.gitignore +++ b/tools/testing/selftests/filesystems/fuse/.gitignore @@ -1,3 +1,4 @@ # SPDX-License-Identifier: GPL-2.0-only fuse_mnt fusectl_test +write_extend_eof_test diff --git a/tools/testing/selftests/filesystems/fuse/Makefile b/tools/testing/selftests/filesystems/fuse/Makefile index 612aad69a93a..0c2c613af0ac 100644 --- a/tools/testing/selftests/filesystems/fuse/Makefile +++ b/tools/testing/selftests/filesystems/fuse/Makefile @@ -3,10 +3,13 @@ CFLAGS += -Wall -O2 -g $(KHDR_INCLUDES) TEST_GEN_PROGS := fusectl_test +TEST_GEN_PROGS += write_extend_eof_test TEST_GEN_FILES := fuse_mnt include ../../lib.mk +$(OUTPUT)/write_extend_eof_test: LDLIBS += -lpthread + VAR_CFLAGS := $(shell pkg-config fuse --cflags 2>/dev/null) ifeq ($(VAR_CFLAGS),) VAR_CFLAGS := -D_FILE_OFFSET_BITS=64 -I/usr/include/fuse diff --git a/tools/testing/selftests/filesystems/fuse/write_extend_eof_test.c b/tools/testing/selftests/filesystems/fuse/write_extend_eof_test.c new file mode 100644 index 000000000000..ca6ce6eca382 --- /dev/null +++ b/tools/testing/selftests/filesystems/fuse/write_extend_eof_test.c @@ -0,0 +1,368 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Regression test for the fuse write-extend partial-EOF-page zeroing bug. + * + * A buffered write that extends i_size past a non-page-aligned EOF must zero + * the tail of the old last page. If an application has mmap'd that page and + * stored into the post-EOF region (undefined until the file grows), the + * now-in-bounds tail must read back as zero, not as the stale stored bytes. + * + * The bug is exposed on a non-writeback_cache server that keeps the page cache + * across the write (FOPEN_KEEP_CACHE without FOPEN_DIRECT_IO). This test is a + * raw /dev/fuse server in that mode; the backing data is always zero in the + * hole, so any non-zero byte a read sees is stale page-cache data. + * + * Requires root to mount fuse. + */ +#define _GNU_SOURCE +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +#include "../../kselftest_harness.h" + +#define FUSE_ROOT_ID 1 +#define FILE_INO 2 +#define MAX_WRITE (128 * 1024) +#define BACKING_SIZE (4 * 1024 * 1024) +#define POLLUTE 0xee + +/* Server-side state, shared with the responder thread. */ +struct server { + int fd; + unsigned char backing[BACKING_SIZE]; /* authoritative bytes */ + uint64_t size; +}; + +static void reply(int fd, uint64_t unique, int error, void *data, size_t len) +{ + struct fuse_out_header oh = { + .len = sizeof(oh) + (data ? len : 0), + .error = error, + .unique = unique, + }; + struct iovec iov[2] = { { &oh, sizeof(oh) }, { data, len } }; + + /* Errors here are teardown races (device closed on unmount); ignore. */ + if (writev(fd, iov, data ? 2 : 1) < 0) + return; +} + +static void fill_attr(struct fuse_attr *a, uint64_t ino, uint32_t mode, + uint64_t size) +{ + memset(a, 0, sizeof(*a)); + a->ino = ino; + a->mode = mode; + a->nlink = 1; + a->size = size; + a->blksize = sysconf(_SC_PAGESIZE); +} + +static void *server_thread(void *arg) +{ + struct server *s = arg; + static char buf[MAX_WRITE + 4096]; + + for (;;) { + ssize_t n = read(s->fd, buf, sizeof(buf)); + struct fuse_in_header *ih = (void *)buf; + + if (n < 0) { + if (errno == EINTR || errno == EAGAIN) + continue; + return NULL; /* device closed on unmount */ + } + if (n < (ssize_t)sizeof(*ih)) + continue; + + switch (ih->opcode) { + case FUSE_INIT: { + struct fuse_init_in *in = (void *)(ih + 1); + struct fuse_init_out out = {0}; + + /* No FUSE_WRITEBACK_CACHE: the exposed configuration. */ + out.major = FUSE_KERNEL_VERSION; + out.minor = FUSE_KERNEL_MINOR_VERSION; + out.max_readahead = in->max_readahead; + out.max_write = MAX_WRITE; + out.max_background = 16; + out.congestion_threshold = 12; + out.flags = FUSE_MAX_PAGES; + out.max_pages = MAX_WRITE / sysconf(_SC_PAGESIZE); + reply(s->fd, ih->unique, 0, &out, sizeof(out)); + break; + } + case FUSE_GETATTR: { + struct fuse_attr_out out = {0}; + int root = ih->nodeid == FUSE_ROOT_ID; + + out.attr_valid = 3600; + fill_attr(&out.attr, ih->nodeid, + root ? (S_IFDIR | 0755) : (S_IFREG | 0644), + root ? 0 : s->size); + reply(s->fd, ih->unique, 0, &out, sizeof(out)); + break; + } + case FUSE_LOOKUP: { + struct fuse_entry_out out = {0}; + + out.nodeid = FILE_INO; + out.attr_valid = 3600; + out.entry_valid = 3600; + fill_attr(&out.attr, FILE_INO, S_IFREG | 0644, s->size); + reply(s->fd, ih->unique, 0, &out, sizeof(out)); + break; + } + case FUSE_OPEN: + case FUSE_OPENDIR: { + struct fuse_open_out out = {0}; + + /* Keep the cache across the write, but not direct I/O. */ + out.open_flags = FOPEN_KEEP_CACHE; + reply(s->fd, ih->unique, 0, &out, sizeof(out)); + break; + } + case FUSE_READ: { + struct fuse_read_in *in = (void *)(ih + 1); + uint64_t off = in->offset; + uint32_t size = in->size; + + if (off >= BACKING_SIZE) + size = 0; + else if (off + size > BACKING_SIZE) + size = BACKING_SIZE - off; + reply(s->fd, ih->unique, 0, s->backing + off, size); + break; + } + case FUSE_WRITE: { + struct fuse_write_in *in = (void *)(ih + 1); + struct fuse_write_out out = {0}; + uint64_t off = in->offset; + uint32_t size = in->size; + + if (off < BACKING_SIZE) { + uint32_t c = size; + + if (off + c > BACKING_SIZE) + c = BACKING_SIZE - off; + memcpy(s->backing + off, in + 1, c); + if (off + c > s->size) + s->size = off + c; + } + out.size = size; + reply(s->fd, ih->unique, 0, &out, sizeof(out)); + break; + } + case FUSE_SETATTR: { + struct fuse_setattr_in *in = (void *)(ih + 1); + struct fuse_attr_out out = {0}; + + if ((in->valid & FATTR_SIZE) && in->size <= BACKING_SIZE) { + if (in->size > s->size) + memset(s->backing + s->size, 0, + in->size - s->size); + s->size = in->size; + } + out.attr_valid = 3600; + fill_attr(&out.attr, ih->nodeid, S_IFREG | 0644, s->size); + reply(s->fd, ih->unique, 0, &out, sizeof(out)); + break; + } + case FUSE_FALLOCATE: { + struct fuse_fallocate_in *in = (void *)(ih + 1); + uint64_t end = in->offset + in->length; + + /* Only plain (size-extending) fallocate is used here. */ + if (!(in->mode & FALLOC_FL_KEEP_SIZE) && + end <= BACKING_SIZE && end > s->size) { + memset(s->backing + s->size, 0, end - s->size); + s->size = end; + } + reply(s->fd, ih->unique, 0, NULL, 0); + break; + } + case FUSE_FLUSH: + case FUSE_RELEASE: + case FUSE_RELEASEDIR: + case FUSE_FSYNC: + case FUSE_ACCESS: + reply(s->fd, ih->unique, 0, NULL, 0); + break; + case FUSE_FORGET: + break; + default: + reply(s->fd, ih->unique, -EOPNOTSUPP, NULL, 0); + break; + } + } +} + +FIXTURE(fuse) +{ + struct server *srv; + pthread_t thread; + char dir[64]; + long page; /* runtime page size */ + off_t eof; /* mid-page EOF, page-relative */ + int fd; /* open test file */ + char *map; /* mmap of the EOF page */ + int mounted; +}; + +FIXTURE_SETUP(fuse) +{ + char opts[128]; + pthread_t t; + + if (geteuid() != 0) + SKIP(return, "need root to mount fuse"); + + self->page = sysconf(_SC_PAGESIZE); + self->fd = -1; + self->map = MAP_FAILED; + + self->srv = mmap(NULL, sizeof(*self->srv), PROT_READ | PROT_WRITE, + MAP_SHARED | MAP_ANONYMOUS, -1, 0); + ASSERT_NE(MAP_FAILED, self->srv); + + self->srv->fd = open("/dev/fuse", O_RDWR); + ASSERT_GE(self->srv->fd, 0); + + strcpy(self->dir, "/tmp/fuse_weof_XXXXXX"); + ASSERT_NE(NULL, mkdtemp(self->dir)); + + snprintf(opts, sizeof(opts), + "fd=%d,rootmode=40000,user_id=0,group_id=0", + self->srv->fd); + ASSERT_EQ(0, mount("fuse", self->dir, "fuse", 0, opts)); + self->mounted = 1; + + ASSERT_EQ(0, pthread_create(&t, NULL, server_thread, self->srv)); + self->thread = t; +} + +FIXTURE_TEARDOWN(fuse) +{ + if (self->map != MAP_FAILED) + munmap(self->map, self->page); + if (self->fd >= 0) + close(self->fd); + if (self->mounted) + umount2(self->dir, MNT_DETACH); + if (self->srv && self->srv != MAP_FAILED) { + if (self->srv->fd > 0) + close(self->srv->fd); + munmap(self->srv, sizeof(*self->srv)); + } + if (self->dir[0]) + rmdir(self->dir); +} + +/* + * Create the test file with a mid-page EOF and mmap-store POLLUTE into its + * post-EOF tail (a legal store, undefined until the file grows). Leaves the + * file open and the EOF page mapped in the fixture for the caller to extend. + */ +static void pollute_eof_tail(struct __test_metadata *_metadata, + FIXTURE_DATA(fuse) * self) +{ + off_t eof = 2 * self->page + self->page / 4; + char path[128]; + char *buf; + + snprintf(path, sizeof(path), "%s/file", self->dir); + self->fd = open(path, O_RDWR | O_CREAT | O_TRUNC, 0644); + ASSERT_GE(self->fd, 0); + self->eof = eof; + + buf = malloc(eof); + ASSERT_NE(NULL, buf); + memset(buf, 'A', eof); + ASSERT_EQ(eof, pwrite(self->fd, buf, eof, 0)); + free(buf); + + self->map = mmap(NULL, self->page, PROT_READ | PROT_WRITE, MAP_SHARED, + self->fd, eof & ~(self->page - 1)); + ASSERT_NE(MAP_FAILED, self->map); + memset(self->map + (eof & (self->page - 1)), POLLUTE, + self->page - (eof & (self->page - 1))); +} + +/* Assert the old post-EOF tail [eof, end of its page) now reads back as zero. */ +static void assert_tail_zeroed(struct __test_metadata *_metadata, + FIXTURE_DATA(fuse) * self) +{ + off_t base = self->eof & ~(self->page - 1); + char *tail = malloc(self->page); + int i; + + ASSERT_NE(NULL, tail); + ASSERT_EQ(self->page, pread(self->fd, tail, self->page, base)); + for (i = self->eof & (self->page - 1); i < self->page; i++) + ASSERT_EQ(0, tail[i]); + free(tail); +} + +/* Basic: pollute the post-EOF tail, extend past it by a later write. */ +TEST_F(fuse, write_extend) +{ + pollute_eof_tail(_metadata, self); + ASSERT_EQ(4, pwrite(self->fd, "data", 4, 5 * self->page + self->page / 3)); + assert_tail_zeroed(_metadata, self); +} + +/* Extend via ftruncate() rather than a write. */ +TEST_F(fuse, ftruncate_extend) +{ + pollute_eof_tail(_metadata, self); + ASSERT_EQ(0, ftruncate(self->fd, 8 * self->page)); + assert_tail_zeroed(_metadata, self); +} + +/* Extend via fallocate() starting at the old EOF. */ +TEST_F(fuse, fallocate_extend) +{ + pollute_eof_tail(_metadata, self); + ASSERT_EQ(0, fallocate(self->fd, 0, self->eof, 4 * self->page)); + assert_tail_zeroed(_metadata, self); +} + +/* A write landing inside the old EOF page must not clobber its own data. */ +TEST_F(fuse, extend_into_eof_page_preserves_data) +{ + off_t base, wr; + char *buf, *rd; + int i; + + pollute_eof_tail(_metadata, self); + base = self->eof & ~(self->page - 1); + wr = base + 3 * self->page / 4; /* starts in the EOF page */ + + buf = malloc(2 * self->page); + ASSERT_NE(NULL, buf); + memset(buf, 'B', 2 * self->page); + ASSERT_EQ(2 * self->page, pwrite(self->fd, buf, 2 * self->page, wr)); + free(buf); + + rd = malloc(self->page); + ASSERT_NE(NULL, rd); + ASSERT_EQ(self->page, pread(self->fd, rd, self->page, base)); + /* [eof, wr) is hole -> zero; [wr, page) is written data -> 'B'. */ + for (i = self->eof & (self->page - 1); i < wr - base; i++) + ASSERT_EQ(0, rd[i]); + for (i = wr - base; i < self->page; i++) + ASSERT_EQ('B', rd[i]); + free(rd); +} + +TEST_HARNESS_MAIN -- 2.50.1