From: Paolo Bonzini Date: Wed, 27 Aug 2008 15:20:35 +0000 (+0200) Subject: make git-shell paranoid about closed stdin/stdout/stderr X-Git-Tag: v1.6.0.2~46 X-Git-Url: https://git.tokkee.org/?a=commitdiff_plain;h=0cfeed2e1d320cc76c434e0bfc26d90065754e46;p=git.git 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 Acked-by: Stephen R. van den Berg Signed-off-by: Junio C Hamano --- diff --git a/shell.c b/shell.c index 6a48de05f..ad60200d2 100644 --- a/shell.c +++ b/shell.c @@ -56,6 +56,19 @@ int main(int argc, char **argv) { char *prog; struct commands *cmd; + int devnull_fd; + + /* + * Always open file descriptors 0/1/2 to avoid clobbering files + * in die(). It also avoids not messing up when the pipes are + * dup'ed onto stdin/stdout/stderr in the child processes we spawn. + */ + devnull_fd = open("/dev/null", O_RDWR); + while (devnull_fd >= 0 && devnull_fd <= 2) + devnull_fd = dup(devnull_fd); + if (devnull_fd == -1) + die("opening /dev/null failed (%s)", strerror(errno)); + close (devnull_fd); /* * Special hack to pretend to be a CVS server