systemd uses malloc_usable_size() everywhere to use memory blocks
obtained through malloc, but that is abuse since the
malloc_usable_size() interface isn't meant for this kind of use, it is
for diagnostics only. This is also why systemd behaviour is flaky when
built with _FORTIFY_SOURCE.
One way to make this more standard (and hence safer) is to, at every
malloc_usable_size() call, also 'reallocate' the block so that the
compiler can see the larger size. This is done through a dummy
reallocator whose only purpose is to tell the compiler about the larger
usable size, it doesn't do any actual reallocation.
Florian Weimer pointed out that this doesn't solve the problem of an
allocator potentially growing usable size at will, which will break the
implicit assumption in systemd use that the value returned remains
constant as long as the object is valid. The safest way to fix that is
for systemd to step away from using malloc_usable_size() like this.
Resolves#22801.
We recently started making more use of malloc_usable_size() and rely on
it (see the string_erase() story). Given that we don't really support
sytems where malloc_usable_size() cannot be trusted beyond statistics
anyway, let's go fully in and rework GREEDY_REALLOC() on top of it:
instead of passing around and maintaining the currenly allocated size
everywhere, let's just derive it automatically from
malloc_usable_size().
I am mostly after this for the simplicity this brings. It also brings
minor efficiency improvements I guess, but things become so much nicer
to look at if we can avoid these allocation size variables everywhere.
Note that the malloc_usable_size() man page says relying on it wasn't
"good programming practice", but I think it does this for reasons that
don't apply here: the greedy realloc logic specifically doesn't rely on
the returned extra size, beyond the fact that it is equal or larger than
what was requested.
(This commit was supposed to be a quick patch btw, but apparently we use
the greedy realloc stuff quite a bit across the codebase, so this ends
up touching *a*lot* of code.)
This is another attempt at d4b604baea and #12438
Instead of blindly using the extra allocated space, let's do so only
after telling libc about it, via a second realloc(). The second
realloc() should be quick, since it never has to copy memory around.
This reverts commit d4b604baea.
When realloc() is called, the extra memory between the originally
requested size and the end of malloc_usable_size() isn't copied. (at
least with the version of glibc that currently ships on Arch Linux)
As a result, some elements get lost and use uninitialized memory, most
commonly 0, and can lead to crashes.
fixes#12384
It's a glibc-specific API, but supported on FreeBSD and musl too at
least, hence fairly common. This way we can reduce our calls to
realloc() as much as possible.
All underlying glibc calls are free to return NULL if the size argument
is 0. We most often call those functions with a fixed argument, or at least
something which obviously cannot be zero, but it's too easy to forget.
E.g. coverity complains about "rows = new0(JsonVariant*, n_rows-1);" in
format-table.c There is an assert that n_rows > 0, so we could hit this
corner case here. Let's simplify callers and make those functions "safe".
CID #1397035.
The compiler is mostly able to optimize this away:
$ size build{,-opt}/src/shared/libsystemd-shared-239.so
(before)
text data bss dec hex filename
2643329 580940 3112 3227381 313ef5 build/src/shared/libsystemd-shared-239.so (-O0 -g)
2170013 578588 3089 2751690 29fcca build-opt/src/shared/libsystemd-shared-239.so (-03 -flto -g)
(after)
text data bss dec hex filename
2644017 580940 3112 3228069 3141a5 build/src/shared/libsystemd-shared-239.so
2170765 578588 3057 2752410 29ff9a build-opt/src/shared/libsystemd-shared-239.so
These lines are generally out-of-date, incomplete and unnecessary. With
SPDX and git repository much more accurate and fine grained information
about licensing and authorship is available, hence let's drop the
per-file copyright notice. Of course, removing copyright lines of others
is problematic, hence this commit only removes my own lines and leaves
all others untouched. It might be nicer if sooner or later those could
go away too, making git the only and accurate source of authorship
information.
This part of the copyright blurb stems from the GPL use recommendations:
https://www.gnu.org/licenses/gpl-howto.en.html
The concept appears to originate in times where version control was per
file, instead of per tree, and was a way to glue the files together.
Ultimately, we nowadays don't live in that world anymore, and this
information is entirely useless anyway, as people are very welcome to
copy these files into any projects they like, and they shouldn't have to
change bits that are part of our copyright header for that.
hence, let's just get rid of this old cruft, and shorten our codebase a
bit.
Files which are installed as-is (any .service and other unit files, .conf
files, .policy files, etc), are left as is. My assumption is that SPDX
identifiers are not yet that well known, so it's better to retain the
extended header to avoid any doubt.
I also kept any copyright lines. We can probably remove them, but it'd nice to
obtain explicit acks from all involved authors before doing that.
These are similar to memdup() and newdup(), but reserve one extra NUL
byte at the end of the new allocation and initialize it. It's useful
when copying out data from fixed size character arrays where NUL
termination can't be assumed.
