Commit Graph

10 Commits (master)

Author SHA1 Message Date
Taylor Blau 60ff56f503 banned.h: mark `strtok()` and `strtok_r()` as banned
`strtok()` has a couple of drawbacks that make it undesirable to have
any new instances. In addition to being thread-unsafe, it also
encourages confusing data flows, where `strtok()` may be called from
multiple functions with its first argument as NULL, making it unclear
from the immediate context which string is being tokenized.

Now that we have removed all instances of `strtok()` from the tree,
let's ban `strtok()` to avoid introducing new ones in the future. If new
callers should arise, they are encouraged to use
`string_list_split_in_place()` (and `string_list_remove_empty_items()`,
if applicable).

string_list_split_in_place() is not a perfect drop-in replacement
for `strtok_r()`, particularly if the caller is processing a string with
an arbitrary number of tokens, and wants to process each token one at a

But there are no instances of this in Git's tree which are more
well-suited to `strtok_r()` than the friendlier
`string_list_split_in_place()`, so ban `strtok_r()`, too.

Signed-off-by: Taylor Blau <>
Signed-off-by: Junio C Hamano <>
2023-04-27 08:51:11 -07:00
Ævar Arnfjörð Bjarmason 56a29d2c97 C99: remove hardcoded-out !HAVE_VARIADIC_MACROS code
Remove the "else" branches of the HAVE_VARIADIC_MACROS macro, which
have been unconditionally omitted since 765dc16888 (git-compat-util:
always enable variadic macros, 2021-01-28).

Since were always omitted, anyone trying to use a compiler without
variadic macro support to compile a git since version
git v2.31.0 or later would have had a compilation error. 10 months
across a few releases since then should have been enough time for
anyone who cared to run into that and report the issue.

In addition to that, for anyone unsetting HAVE_VARIADIC_MACROS we've
been emitting extremely verbose warnings since at least
ee4512ed48 (trace2: create new combined trace facility,
2019-02-22). That's because there is no such thing as a
"region_enter_printf" or "region_leave_printf" format, so at least
under GCC and Clang everything that includes trace.h (almost every
file) emits a couple of warnings about that.

There's a large benefit to being able to have a hard dependency rely
on variadic macros, the code surrounding usage.c is hard to maintain
if we need to write two implementations of everything, and by relying
on "__FILE__" and "__LINE__" along with "__VA_ARGS__" we can in the
future make error(), die() etc. log where they were called from. We've
also recently merged d67fc4bf0b (Merge branch 'bc/require-c99',
2021-12-10) which further cements our hard dependency on C99.

So let's delete the fallback code, and update our CodingGuidelines to
note that we depend on this. The added bullet-point starts with
lower-case for consistency with other bullet-points in that section.

The diff in "trace.h" is relatively hard to read, since we need to
retain the existing API docs, which were comments on the code used if
HAVE_VARIADIC_MACROS was not defined.

Signed-off-by: Ævar Arnfjörð Bjarmason <>
Signed-off-by: Junio C Hamano <>
2022-02-21 19:14:19 -08:00
Jeff King 91aef03015 banned.h: mark ctime_r() and asctime_r() as banned
The ctime_r() and asctime_r() functions are reentrant, but have
no check that the buffer we pass in is long enough (the manpage says it
"should have room for at least 26 bytes"). Since this is such an
easy-to-get-wrong interface, and since we have the much safer strftime()
as well as its more convenient strbuf_addftime() wrapper, let's ban both
of those.

Signed-off-by: Jeff King <>
Reviewed-by: Taylor Blau <>
Signed-off-by: Junio C Hamano <>
2020-12-02 14:30:39 -08:00
Jeff King 1fbfdf556f banned.h: mark non-reentrant gmtime, etc as banned
The traditional gmtime(), localtime(), ctime(), and asctime() functions
return pointers to shared storage. This means they're not thread-safe,
and they also run the risk of somebody holding onto the result across
multiple calls (where each call invalidates the previous result).

All callers should be using their reentrant counterparts.

Signed-off-by: Jeff King <>
Reviewed-by: Taylor Blau <>
Signed-off-by: Junio C Hamano <>
2020-12-01 14:37:27 -08:00
Taylor Blau 60d198d022 banned.h: fix vsprintf()'s ban message
In cc8fdaee1e (banned.h: mark sprintf() as banned, 2018-07-24), both
'sprintf()' and 'vsprintf()' were marked as banned functions. The
non-variadic macro to ban 'vsprintf' has a typo which says that
'sprintf', not 'vsprintf' is banned. The variadic version does not have
the same typo.

Fix this by updating the explicit form of 'vsprintf' as the banned
version of itself, not 'sprintf'.

Signed-off-by: Taylor Blau <>
Signed-off-by: Junio C Hamano <>
2019-08-26 10:32:45 -07:00
Eric Wong ace5707a80 banned.h: mark strncat() as banned
strncat() has the same quadratic behavior as strcat() and is
difficult-to-read and bug-prone.  While it hasn't yet been a
problem in git iself, strncat() found it's way into 'master'
of cgit and caused segfaults on my system.

Signed-off-by: Eric Wong <>
Signed-off-by: Junio C Hamano <>
2019-01-02 10:19:05 -08:00
Jeff King e488b7aba7 banned.h: mark strncpy() as banned
The strncpy() function is less horrible than strcpy(), but
is still pretty easy to misuse because of its funny
termination semantics. Namely, that if it truncates it omits
the NUL terminator, and you must remember to add it
yourself. Even if you use it correctly, it's sometimes hard
for a reader to verify this without hunting through the
code. If you're thinking about using it, consider instead:

  - strlcpy() if you really just need a truncated but
    NUL-terminated string (we provide a compat version, so
    it's always available)

  - xsnprintf() if you're sure that what you're copying
    should fit

  - strbuf or xstrfmt() if you need to handle
    arbitrary-length heap-allocated strings

Note that there is one instance of strncpy in
compat/regex/regcomp.c, which is fine (it allocates a
sufficiently large string before copying). But this doesn't
trigger the ban-list even when compiling with NO_REGEX=1,

  1. we don't use git-compat-util.h when compiling it
     (instead we rely on the system includes from the
     upstream library); and

  2. It's in an "#ifdef DEBUG" block

Since it's doesn't trigger the banned.h code, we're better
off leaving it to keep our divergence from upstream minimal.

Signed-off-by: Jeff King <>
Signed-off-by: Junio C Hamano <>
2018-07-26 10:12:51 -07:00
Jeff King cc8fdaee1e banned.h: mark sprintf() as banned
The sprintf() function (and its variadic form vsprintf) make
it easy to accidentally introduce a buffer overflow. If
you're thinking of using them, you're better off either
using a dynamic string (strbuf or xstrfmt), or xsnprintf if
you really know that you won't overflow. The last sprintf()
call went away quite a while ago in f0766bf94e (fsck: use
for_each_loose_file_in_objdir, 2015-09-24).

Note that we respect HAVE_VARIADIC_MACROS here, which some
ancient platforms lack. As a fallback, we can just "guess"
that the caller will provide 3 arguments. If they do, then
the macro will work as usual. If not, then they'll get a
slightly less useful error, like:

  git.c:718:24: error: macro "sprintf" passed 3 arguments, but takes just 2

That's not ideal, but it at least alerts them to the problem
area. And anyway, we're primarily targeting people adding
new code. Most developers should be on modern enough
platforms to see the normal "good" error message.

Signed-off-by: Jeff King <>
Signed-off-by: Junio C Hamano <>
2018-07-26 10:12:51 -07:00
Jeff King 1b11b64b81 banned.h: mark strcat() as banned
The strcat() function has all of the same overflow problems
as strcpy(). And as a bonus, it's easy to end up
accidentally quadratic, as each subsequent call has to walk
through the existing string.

The last strcat() call went away in f063d38b80 (daemon: use
cld->env_array when re-spawning, 2015-09-24). In general,
strcat() can be replaced either with a dynamic string
(strbuf or xstrfmt), or with xsnprintf if you know the
length is bounded.

Signed-off-by: Jeff King <>
Signed-off-by: Junio C Hamano <>
2018-07-26 10:12:50 -07:00
Jeff King c8af66ab8a automatically ban strcpy()
There are a few standard C functions (like strcpy) which are
easy to misuse. E.g.:

  char path[PATH_MAX];
  strcpy(path, arg);

may overflow the "path" buffer. Sometimes there's an earlier
constraint on the size of "arg", but even in such a case
it's hard to verify that the code is correct. If the size
really is unbounded, you're better off using a dynamic
helper like strbuf:

  struct strbuf path = STRBUF_INIT;
  strbuf_addstr(path, arg);

or if it really is bounded, then use xsnprintf to show your
expectation (and get a run-time assertion):

  char path[PATH_MAX];
  xsnprintf(path, sizeof(path), "%s", arg);

which makes further auditing easier.

We'd usually catch undesirable code like this in a review,
but there's no automated enforcement. Adding that
enforcement can help us be more consistent and save effort
(and a round-trip) during review.

This patch teaches the compiler to report an error when it
sees strcpy (and will become a model for banning a few other
functions). This has a few advantages over a separate
linting tool:

  1. We know it's run as part of a build cycle, so it's
     hard to ignore. Whereas an external linter is an extra
     step the developer needs to remember to do.

  2. Likewise, it's basically free since the compiler is
     parsing the code anyway.

  3. We know it's robust against false positives (unlike a
     grep-based linter).

The two big disadvantages are:

  1. We'll only check code that is actually compiled, so it
     may miss code that isn't triggered on your particular
     system. But since presumably people don't add new code
     without compiling it (and if they do, the banned
     function list is the least of their worries), we really
     only care about failing to clean up old code when
     adding new functions to the list. And that's easy
     enough to address with a manual audit when adding a new
     function (which is what I did for the functions here).

  2. If this ends up generating false positives, it's going
     to be harder to disable (as opposed to a separate
     linter, which may have mechanisms for overriding a
     particular case).

     But the intent is to only ban functions which are
     obviously bad, and for which we accept using an
     alternative even when this particular use isn't buggy
     (e.g., the xsnprintf alternative above).

The implementation here is simple: we'll define a macro for
the banned function which replaces it with a reference to a
descriptively named but undeclared identifier.  Replacing it
with any invalid code would work (since we just want to
break compilation).  But ideally we'd meet these goals:

 - it should be portable; ideally this would trigger
   everywhere, and does not need to be part of a DEVELOPER=1
   setup (because unlike warnings which may depend on the
   compiler or system, this is a clear indicator of
   something wrong in the code).

 - it should generate a readable error that gives the
   developer a clue what happened

 - it should avoid generating too much other cruft that
   makes it hard to see the actual error

 - it should mention the original callsite in the error

The output with this patch looks like this (using gcc 7, on
a checkout with 022d2ac1f3 reverted, which removed the final
strcpy from blame.c):

      CC builtin/blame.o
  In file included from ./git-compat-util.h:1246,
                   from ./cache.h:4,
                   from builtin/blame.c:8:
  builtin/blame.c: In function ‘cmd_blame’:
  ./banned.h:11:22: error: ‘sorry_strcpy_is_a_banned_function’ undeclared (first use in this function)
   #define BANNED(func) sorry_##func##_is_a_banned_function
  ./banned.h:14:21: note: in expansion of macro ‘BANNED’
   #define strcpy(x,y) BANNED(strcpy)
  builtin/blame.c:1074:4: note: in expansion of macro ‘strcpy’
      strcpy(repeated_meta_color, GIT_COLOR_CYAN);
  ./banned.h:11:22: note: each undeclared identifier is reported only once for each function it appears in
   #define BANNED(func) sorry_##func##_is_a_banned_function
  ./banned.h:14:21: note: in expansion of macro ‘BANNED’
   #define strcpy(x,y) BANNED(strcpy)
  builtin/blame.c:1074:4: note: in expansion of macro ‘strcpy’
      strcpy(repeated_meta_color, GIT_COLOR_CYAN);

This prominently shows the phrase "strcpy is a banned
function", along with the original callsite in blame.c and
the location of the ban code in banned.h. Which should be
enough to get even a developer seeing this for the first
time pointed in the right direction.

This doesn't match our ideals perfectly, but it's a pretty
good balance. A few alternatives I tried:

  1. Instead of using an undeclared variable, using an
     undeclared function. This shortens the message, because
     the "each undeclared identifier" message is not needed
     (and as you can see above, it triggers a separate
     mention of each of the expansion points).

     But it doesn't actually stop compilation unless you use
     -Werror=implicit-function-declaration in your CFLAGS.
     This is the case for DEVELOPER=1, but not for a default
     build (on the other hand, we'd eventually produce a
     link error pointing to the correct source line with the
     descriptive name).

  2. The linux kernel uses a similar mechanism in its
     BUILD_BUG_ON_MSG(), where they actually declare the
     function but do so with gcc's error attribute. But
     that's not portable to other compilers (and it also
     runs afoul of our error() macro).

     We could make a gcc-specific technique and fallback on
     other compilers, but it's probably not worth the
     complexity. It also isn't significantly shorter than
     the error message shown above.

  3. We could drop the BANNED() macro, which would shorten
     the number of lines in the error. But curiously,
     removing it (and just expanding strcpy directly to the
     bogus identifier) causes gcc _not_ to report the
     original line of code.

So this strategy seems to be an acceptable mix of
information, portability, simplicity, and robustness,
without _too_ much extra clutter. I also tested it with
clang, and it looks as good (actually, slightly less
cluttered than with gcc).

Signed-off-by: Jeff King <>
Signed-off-by: Junio C Hamano <>
2018-07-26 10:12:09 -07:00