[File] file-5.46 segfault on Cygwin (only)

[raf]

On Sat, Jun 06, 2026 at 01:56:33PM +0200, Christoph Biedl <astron.com.bwoj at manchmal.in-ulm.de> wrote:

> raf wrote...
> 
> > Strangely, 5.46 on macOS and Debian don't crash with this file.
> > It's just the 5.46 on Cygwin.
> > 
> > I compiled 5.46 on Cygwin myself to see if it's something
> > wrong just with the Cygwin package of file-devel but that
> > crashed too.
> > 
> > 5.47 on all three systems doesn't crash, so that's good.
> 
> Out of curiosity, were you able to bisect to identify the commit that
> fixed the issue?
> 
>     Christoph

Hi Christoph,

No, I just used 5.46 and 5.47 from the ftp site.

While bisecting, I came across this commit which looked promising:

  [1550a570cbe35c5d2520fe812e4871c596c74f14] PR/578: Don't crash on cygwin when tm_mon == -1

But that didn't compile because of:

  libtool: compile:  gcc -DHAVE_CONFIG_H -I. -I.. -DMAGIC=\"/usr/local/share/misc/magic\" -fvisibility=hidden -Wall -Wstrict-prototypes -Wmissing-prototypes -Wpointer-arith -Wmissing-declarations -Wredundant-decls -Wnested-externs -Wsign-compare -Wreturn-type -Wswitch -Wshadow -Wcast-qual -Wwrite-strings -Wextra -Wunused-parameter -Wformat=2 -g -O2 -MT print.lo -MD -MP -MF .deps/print.Tpo -c print.c  -DDLL_EXPORT -DPIC -o .libs/print.o
  print.c: In function 'file_fmtdate':
  print.c:357:32: error: invalid type argument of '->' (have 'struct tm')
    357 |         if (tm.tm_mon < 0 && tm->tm_mon > 11)
        |                                ^~

The first testable commit that's fixed is:

  ef18b1218393210ae7a7f83c82d69f82c62a3941 is the first new commit
  commit ef18b1218393210ae7a7f83c82d69f82c62a3941
  Author: Christos Zoulas <christos at zoulas.com>
  Date:   Mon Dec 9 06:22:27 2024

      fix wrong logic.

So presumably it was 1550a570 that started the fix:

@@ -352,6 +352,10 @@ file_fmtdate(char *buf, size_t bsize, uint16_t v)
        memset(&tm, 0, sizeof(tm));
        tm.tm_mday = v & 0x1f;
        tm.tm_mon = ((v >> 5) & 0xf) - 1;
+       // Sanity check because some OS's coredump with invalid values.
+       // Yes, Cygwin I am looking at you!
+       if (tm.tm_mon < 0 && tm->tm_mon > 11)
+               tm.tm_mon = 0;
        tm.tm_year = (v >> 9) + 80;

        if (strftime(buf, bsize, "%a, %b %d %Y", &tm) == 0)

That had a typo that stopped subsequent commits from compiling.
The -> error was fixed later, and ef18b1218 fixed the && error:

-       if (tm.tm_mon < 0 && tm.tm_mon > 11)
+       if (tm.tm_mon < 0 || tm.tm_mon > 11)

cheers,
raf