Re: [libvirt] [PATCHv2] Eliminate large stack buffer in doTunnelSendAll

doTunnelSendAll function (used by QEMU migration) uses a 64k buffer on the stack, which could be problematic. This patch replaces that with a buffer from the heap. While in the neighborhood, this patch also improves error reporting in the case that saferead fails - previously, virStreamAbort() was called (resetting errno) before reporting the error. It's been changed to report the error first. --- Eric noticed that I was inconsistent in the ordering of cleanup vs. error reporting, so I fixed that in this version. src/qemu/qemu_driver.c | 18 +++++++++++++++--- 1 files changed, 15 insertions(+), 3 deletions(-) diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c index bb3edde..5a18938 100644 --- a/src/qemu/qemu_driver.c +++ b/src/qemu/qemu_driver.c @@ -8399,19 +8399,28 @@ cleanup: } +#define TUNNEL_SEND_BUF_SIZE 65536 + static int doTunnelSendAll(virStreamPtr st, int sock) { - char buffer[65536]; - int nbytes = sizeof(buffer); + char *buffer; + int nbytes = TUNNEL_SEND_BUF_SIZE; + + if (VIR_ALLOC_N(buffer, TUNNEL_SEND_BUF_SIZE) < 0) { + virReportOOMError(); + virStreamAbort(st); + return -1; + } /* XXX should honour the 'resource' parameter here */ for (;;) { nbytes = saferead(sock, buffer, nbytes); if (nbytes < 0) { - virStreamAbort(st); virReportSystemError(errno, "%s", _("tunnelled migration failed to read from qemu")); + virStreamAbort(st); + VIR_FREE(buffer); return -1; } else if (nbytes == 0) @@ -8421,10 +8430,13 @@ static int doTunnelSendAll(virStreamPtr st, if (virStreamSend(st, buffer, nbytes) < 0) { qemuReportError(VIR_ERR_OPERATION_FAILED, "%s", _("Failed to write migration data to remote libvirtd")); + VIR_FREE(buffer); return -1; } } + VIR_FREE(buffer); + if (virStreamFinish(st) < 0) /* virStreamFinish set the error for us */ return -1;