make git-shell paranoid about closed stdin/stdout/stderr

It is in general unsafe to start a program with one or more of file descriptors 0/1/2 closed. Karl Chen for example noticed that stat_command does this in order to rename a pipe file descriptor to 0: dup2(from, 0); close(from); ... but if stdin was closed (for example) from == 0, so that dup2(0, 0); close(0); just ends up closing the pipe. Another extremely rare but nasty problem would occur if an "important" file ends up in file descriptor 2, and is corrupted by a call to die(). Fixing this in git was considered to be overkill, so this patch works around it only for git-shell. The fix is simply to open all the "low" descriptors to /dev/null in main. Signed-off-by: Paolo Bonzini <bonzini@gnu.org> Acked-by: Stephen R. van den Berg <srb@cuci.nl> Signed-off-by: Junio C Hamano <gitster@pobox.com>

Paolo Bonzini committed Aug 27, 2008 at 17:20 UTC 0cfeed2e1d320cc76c434e0bfc26d90065754e46

1 file changed +13

shell.c

+13

@@ -56,6 +56,19 @@ int main(int argc, char **argv)

56 {

57 char *prog;

58 struct commands *cmd;

59 + int devnull_fd;

60 +

61 + /*

62 + * Always open file descriptors 0/1/2 to avoid clobbering files

63 + * in die(). It also avoids not messing up when the pipes are

64 + * dup'ed onto stdin/stdout/stderr in the child processes we spawn.

65 + */

66 + devnull_fd = open("/dev/null", O_RDWR);

67 + while (devnull_fd >= 0 && devnull_fd <= 2)

68 + devnull_fd = dup(devnull_fd);

69 + if (devnull_fd == -1)

70 + die("opening /dev/null failed (%s)", strerror(errno));

71 + close (devnull_fd);

73 /*

74 * Special hack to pretend to be a CVS server