Right now dump_emit() is the only coredump helper that writes buffers larger than a page in one call. For elf notes that can easily blow past PAGE_SIZE. That's annoying because neither pipes nor af_unix sockets take such writes in one piece.
If a signal arrives while the writer is waiting they drop a short write. With the coredump records work coming up that means header and its data are desynchronized. A write that fits in one pipe buffer or one skb doesn't suffer from this. So split all writes up, including elf notes, and cap every write at a page. The coredump socket already raises sk_sndbuf far enough for a page to fit a single skb and pipes always work that way. That means dump_interrupted() is now checked once per page. So a large coredump stops earlier (good). An empty write no longer issues a zero-length write. The rlimit core check stays where it was. It continues refusing whole writes. Signed-off-by: Christian Brauner (Amutable) <[email protected]> --- fs/coredump.c | 37 ++++++++++++++++++++++++++++++------- 1 file changed, 30 insertions(+), 7 deletions(-) diff --git a/fs/coredump.c b/fs/coredump.c index d837819031ff..d61f36239f91 100644 --- a/fs/coredump.c +++ b/fs/coredump.c @@ -1215,19 +1215,21 @@ void vfs_coredump(const kernel_siginfo_t *siginfo) * do on a core-file: use only these functions to write out all the * necessary info. */ -static bool __dump_emit(struct coredump_params *cprm, const void *addr, int nr) +/* One write, never more than a page. See __dump_emit(). */ +static bool dump_emit_chunk(struct coredump_params *cprm, const void *addr, + int nr) { struct file *file = cprm->file; loff_t pos = file->f_pos; ssize_t n; - if (cprm->written + nr > cprm->limit) - return false; if (dump_interrupted()) return false; + n = __kernel_write(file, addr, nr, &pos); if (n != nr) return false; + file->f_pos = pos; cprm->written += n; cprm->pos += n; @@ -1235,6 +1237,24 @@ static bool __dump_emit(struct coredump_params *cprm, const void *addr, int nr) return true; } +static bool __dump_emit(struct coredump_params *cprm, const void *addr, int nr) +{ + if (cprm->written + nr > cprm->limit) + return false; + + while (nr) { + int chunk = min_t(int, nr, PAGE_SIZE); + + if (!dump_emit_chunk(cprm, addr, chunk)) + return false; + + addr += chunk; + nr -= chunk; + } + + return true; +} + static bool __dump_skip(struct coredump_params *cprm, size_t nr) { static char zeroes[PAGE_SIZE]; @@ -1247,13 +1267,16 @@ static bool __dump_skip(struct coredump_params *cprm, size_t nr) return true; } - while (nr > PAGE_SIZE) { - if (!__dump_emit(cprm, zeroes, PAGE_SIZE)) + while (nr) { + size_t chunk = min_t(size_t, nr, PAGE_SIZE); + + if (!__dump_emit(cprm, zeroes, chunk)) return false; - nr -= PAGE_SIZE; + + nr -= chunk; } - return __dump_emit(cprm, zeroes, nr); + return true; } /* Flush the accumulated hole before writing data. */ -- 2.53.0
