On 5/31/22 14:26, Ani Sinha wrote: > On Tue, May 31, 2022 at 5:20 PM Claudio Fontana <[email protected]> wrote: >> >> the code in pcibus_get_fw_dev_path contained the potential for a >> stack buffer overflow of 1 byte, potentially writing to the stack an >> extra NUL byte. >> >> This overflow could happen if the PCI slot is >= 0x10000000, >> and the PCI function is >= 0x10000000, due to the size parameter >> of snprintf being incorrectly calculated in the call: >> >> if (PCI_FUNC(d->devfn)) >> snprintf(path + off, sizeof(path) + off, ",%x", PCI_FUNC(d->devfn)); >> >> since the off obtained from a previous call to snprintf is added >> instead of subtracted from the total available size of the buffer. >> >> Without the accurate size guard from snprintf, we end up writing in the >> worst case: >> >> name (32) + "@" (1) + SLOT (8) + "," (1) + FUNC (8) + term NUL (1) = 51 bytes >> >> In order to provide something more robust, replace all of the code in >> pcibus_get_fw_dev_path with a single call to g_strdup_printf, >> so there is no need to rely on manual calculations. >> >> Found by compiling QEMU with FORTIFY_SOURCE=3 as the error: >> >> *** buffer overflow detected ***: terminated >> >> Thread 1 "qemu-system-x86" received signal SIGABRT, Aborted. >> [Switching to Thread 0x7ffff642c380 (LWP 121307)] >> 0x00007ffff71ff55c in __pthread_kill_implementation () from /lib64/libc.so.6 >> (gdb) bt >> #0 0x00007ffff71ff55c in __pthread_kill_implementation () at >> /lib64/libc.so.6 >> #1 0x00007ffff71ac6f6 in raise () at /lib64/libc.so.6 >> #2 0x00007ffff7195814 in abort () at /lib64/libc.so.6 >> #3 0x00007ffff71f279e in __libc_message () at /lib64/libc.so.6 >> #4 0x00007ffff729767a in __fortify_fail () at /lib64/libc.so.6 >> #5 0x00007ffff7295c36 in () at /lib64/libc.so.6 >> #6 0x00007ffff72957f5 in __snprintf_chk () at /lib64/libc.so.6 >> #7 0x0000555555b1c1fd in pcibus_get_fw_dev_path () >> #8 0x0000555555f2bde4 in qdev_get_fw_dev_path_helper.constprop () >> #9 0x0000555555f2bd86 in qdev_get_fw_dev_path_helper.constprop () >> #10 0x00005555559a6e5d in get_boot_device_path () >> #11 0x00005555559a712c in get_boot_devices_list () >> #12 0x0000555555b1a3d0 in fw_cfg_machine_reset () >> #13 0x0000555555bf4c2d in pc_machine_reset () >> #14 0x0000555555c66988 in qemu_system_reset () >> #15 0x0000555555a6dff6 in qdev_machine_creation_done () >> #16 0x0000555555c79186 in qmp_x_exit_preconfig.part () >> #17 0x0000555555c7b459 in qemu_init () >> #18 0x0000555555960a29 in main () >> >> Found-by: Dario Faggioli <Dario Faggioli <[email protected]> >> Found-by: Martin Liška <[email protected]> > > I think Reported-by: is preferred. > >> Cc: [email protected] >> Signed-off-by: Claudio Fontana <[email protected]> >> --- >> hw/pci/pci.c | 18 +++++++++--------- >> 1 file changed, 9 insertions(+), 9 deletions(-) >> >> diff --git a/hw/pci/pci.c b/hw/pci/pci.c >> index a9b37f8000..6e7015329c 100644 >> --- a/hw/pci/pci.c >> +++ b/hw/pci/pci.c >> @@ -2640,15 +2640,15 @@ static char *pci_dev_fw_name(DeviceState *dev, char >> *buf, int len) >> static char *pcibus_get_fw_dev_path(DeviceState *dev) >> { >> PCIDevice *d = (PCIDevice *)dev; >> - char path[50], name[33]; >> - int off; >> - >> - off = snprintf(path, sizeof(path), "%s@%x", >> - pci_dev_fw_name(dev, name, sizeof name), >> - PCI_SLOT(d->devfn)); >> - if (PCI_FUNC(d->devfn)) >> - snprintf(path + off, sizeof(path) + off, ",%x", PCI_FUNC(d->devfn)); >> - return g_strdup(path); >> + char name[33]; >> + int has_func = !!PCI_FUNC(d->devfn); >> + >> + return g_strdup_printf("%s@%x%s%.*x", > > I was experimenting with printf dynamic precision field with hex and > it was not quite working as expected. In particular, with precision 0, > I was still able to print a single hex digit. That is the following > still outputs 5 in stderr : > >> fprintf(stderr, "%.*x\n", 0, 5);
Hi Ani, both the precision and the value need to be zero to omit the value, and this is what the patch relies on. Ciao, Claudio > > >> + pci_dev_fw_name(dev, name, sizeof(name)), >> + PCI_SLOT(d->devfn), >> + has_func ? "," : "", >> + has_func, >> + PCI_FUNC(d->devfn)); >> } >> >> static char *pcibus_get_dev_path(DeviceState *dev) >> -- >> 2.26.2 >> >>
