Make use of COREDUMP_SPARSE. Refuse it without COREDUMP_RECORDS. Actual holes are sent as a record with length indicating how much zero data there was.
coredump_write() flushes a trailing hole if the coredump is done. Instead of writing the actual byte for pipes and sockets, collapse it. This stops wasting a header with coredump records for a single byte. So we now only write it when the coredump can be seeked. TL;DR a trailing hole is a zero record like any other and the records still cover the whole coredump. Signed-off-by: Christian Brauner (Amutable) <[email protected]> --- fs/coredump.c | 41 +++++++++++++++++----- .../selftests/coredump/coredump_test_helpers.c | 3 +- 2 files changed, 35 insertions(+), 9 deletions(-) diff --git a/fs/coredump.c b/fs/coredump.c index b1679930094c..7b568d25887c 100644 --- a/fs/coredump.c +++ b/fs/coredump.c @@ -68,6 +68,7 @@ static bool dump_vma_snapshot(struct coredump_params *cprm); static void free_vma_snapshot(struct coredump_params *cprm); static void dump_end_record(struct coredump_params *cprm); +static bool dump_flush_skip(struct coredump_params *cprm); #define CORE_FILE_NOTE_SIZE_DEFAULT (4*1024*1024) /* Define a reasonable max cap */ @@ -806,7 +807,7 @@ static bool coredump_sock_request(struct core_name *cn, struct coredump_params * .size = sizeof(struct coredump_req), .mask = COREDUMP_KERNEL | COREDUMP_USERSPACE | COREDUMP_REJECT | COREDUMP_WAIT | - COREDUMP_RECORDS, + COREDUMP_RECORDS | COREDUMP_SPARSE, .size_ack = sizeof(struct coredump_ack), }; struct coredump_ack ack = {}; @@ -866,6 +867,12 @@ static bool coredump_sock_request(struct core_name *cn, struct coredump_params * return false; } + /* Zero records only exist inside a record stream. */ + if ((ack.mask & COREDUMP_SPARSE) && !(ack.mask & COREDUMP_RECORDS)) { + coredump_sock_mark(cprm->file, COREDUMP_MARK_CONFLICTING); + return false; + } + /* Record header scratch; a bvec can't point at the stack. */ if (ack.mask & COREDUMP_RECORDS) { cprm->record_hdr = kmalloc_obj(*cprm->record_hdr); @@ -1076,15 +1083,21 @@ static bool coredump_write(struct coredump_params *cprm, if (!binfmt->core_dump(cprm)) cprm->state |= COREDUMP_STATE_TRUNCATED; /* - * Ensures that file size is big enough to contain the current - * file position. This prevents gdb from complaining about - * a truncated file if the last "write" to the file was - * dump_skip. A record stream relies on it too: the flush - * emits the records that cover a trailing hole. + * A trailing hole still has to land in the coredump. Seeking over + * it doesn't grow the file, so the last byte of it is written + * instead and gdb doesn't see a truncated file. Everything else + * puts the hole on the wire as it flushes it. */ if (cprm->to_skip) { - cprm->to_skip--; - if (!dump_emit(cprm, "", 1)) + bool flushed; + + if (cprm->file->f_mode & FMODE_LSEEK) { + cprm->to_skip--; + flushed = dump_emit(cprm, "", 1); + } else { + flushed = dump_flush_skip(cprm); + } + if (!flushed) cprm->state |= COREDUMP_STATE_TRUNCATED; } dump_end_record(cprm); @@ -1241,6 +1254,11 @@ static bool dump_records(const struct coredump_params *cprm) return cprm->mask & COREDUMP_RECORDS; } +static bool dump_sparse(const struct coredump_params *cprm) +{ + return cprm->mask & COREDUMP_SPARSE; +} + /* Describe the next @len bytes of the coredump. Returns the header size. */ static size_t dump_record_init(struct coredump_params *cprm, enum coredump_record_type type, u64 flags, @@ -1357,6 +1375,13 @@ static bool __dump_skip(struct coredump_params *cprm, size_t nr) static char zeroes[PAGE_SIZE]; struct file *file = cprm->file; + if (dump_sparse(cprm)) { + /* Hand the server the length of the hole instead of the hole itself. */ + if (dump_interrupted()) + return false; + return dump_emit_record(cprm, COREDUMP_RECORD_ZERO, 0, nr); + } + if (file->f_mode & FMODE_LSEEK) { if (dump_interrupted() || vfs_llseek(file, nr, SEEK_CUR) < 0) return false; diff --git a/tools/testing/selftests/coredump/coredump_test_helpers.c b/tools/testing/selftests/coredump/coredump_test_helpers.c index 1c8658f35735..a5b9cde47239 100644 --- a/tools/testing/selftests/coredump/coredump_test_helpers.c +++ b/tools/testing/selftests/coredump/coredump_test_helpers.c @@ -275,7 +275,8 @@ bool send_coredump_ack(int fd, const struct coredump_req *req, /* Every option the kernel is expected to advertise in coredump_req->mask. */ #define TEST_REQ_MASK_ALL \ (COREDUMP_KERNEL | COREDUMP_USERSPACE | \ - COREDUMP_REJECT | COREDUMP_WAIT | COREDUMP_RECORDS) + COREDUMP_REJECT | COREDUMP_WAIT | \ + COREDUMP_RECORDS | COREDUMP_SPARSE) bool check_coredump_req(const struct coredump_req *req) { -- 2.53.0
