These APIs allow you to capture output from guest commands that
generate more output than the protocol limit allows.
Thanks: Nijin Ashok
Fixes: https://issues.redhat.com/browse/RHEL-80159
All recent compilers support this (except MS compilers which we don't
care about). Assume it is supported. We test it in ./configure and
hard fail if it doesn't work.
We still define HAVE_ATTRIBUTE_CLEANUP but you can now assume it is
always defined and don't have to check it.
GUESTFSD_EXT_CMD was used by OpenSUSE to track which external commands
are run by the daemon and package those commands into the appliance.
It is no longer used by recent SUSE builds, so remove it.
Thanks: Pino Toscano, Olaf Hering.
In every instance where we used the ‘cancel_stmt’ parameter of
these macros:
ABS_PATH
NEED_ROOT
the value was only ever ‘cancel_receive ()’ or empty. We only use
‘cancel_receive’ for FileIn functions, so replace it with a simple
flag for whether the current function is a FileIn function.
This also removes some incorrect comments about macros that cannot be
used with FileIn functions when in fact they can.
GCC has two warnings related to large stack frames. We were already
using the -Wframe-larger-than warning, but this reduces the threshold
from 10000 to 5000 bytes.
However that warning only covers the static part of frames (not
alloca). So this change also enables -Wstack-usage=10000 which covers
both the static and dynamic usage (alloca and variable length arrays).
Multiple changes are made throughout the code to reduce frames to fit
within these new limits.
Note that stack allocation of large strings can be a security issue.
For example, we had code like:
size_t len = strlen (fs->windows_systemroot) + 64;
char software[len];
snprintf (software, len, "%s/system32/config/software",
fs->windows_systemroot);
where fs->windows_systemroot is guest controlled. It's not clear what
the effects might be of allowing the guest to allocate potentially
very large stack frames, but at best it allows the guest to cause
libguestfs to segfault. It turns out we are very lucky that
fs->windows_systemroot cannot be set arbitrarily large (see checks in
is_systemroot).
This commit changes those to large heap allocations instead.
