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

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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>
This commit is contained in:
Paolo Bonzini 2008-08-27 17:20:35 +02:00 committed by Junio C Hamano
parent 29f28151c5
commit 0cfeed2e1d
1 changed files with 13 additions and 0 deletions
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13
shell.c
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@ -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