12:35 p.m.
On Wednesday 02 December 2015 17:44:13 Mateusz Guzik wrote:
On Wed, Dec 02, 2015 at 02:00:57PM +0100, Pino Toscano wrote:
> - add a flag to request chroot for the process, which is done only as
> very last (before chdir) operation before exec'ing the process in the
> child: this avoids using CHROOT_IN & CHROOT_OUT around command*
> invocations, and reduces the code spent in chroot mode
> - add failure checks for dup2 and open done in child, not proceeding to
> executing the process if they fail
> - open /dev/null without O_CLOEXEC, so it stays available for the
> exec'ed process, and thus we don't need to provide an own fd for stdin
>
> Followup of commit fd2f175ee79d29df101d353e2f380db27b19553a, thanks also
> to the notes and hints provided by Mateusz Guzik.
Looks good, thanks. I only have optional nits.
> ---
> daemon/command.c | 17 ++---------------
> daemon/daemon.h | 1 +
> daemon/guestfsd.c | 39 +++++++++++++++++++++++++++++++--------
> 3 files changed, 34 insertions(+), 23 deletions(-)
>
> diff --git a/daemon/command.c b/daemon/command.c
> index 27a4d0c..c4efa5b 100644
> --- a/daemon/command.c
> +++ b/daemon/command.c
> @@ -244,7 +244,7 @@ do_command (char *const *argv)
> {
> char *out;
> CLEANUP_FREE char *err = NULL;
> - int r, dev_null_fd, flags;
> + int r, flags;
> CLEANUP_BIND_STATE struct bind_state bind_state = { .mounted = false };
> CLEANUP_RESOLVER_STATE struct resolver_state resolver_state =
> { .mounted = false };
> @@ -261,17 +261,6 @@ do_command (char *const *argv)
> return NULL;
> }
>
> - /* Provide /dev/null as stdin for the command, since we want
> - * to make sure processes have an open stdin, and it is not
> - * possible to rely on the guest to provide it (Linux guests
> - * get /dev dynamically populated at runtime by udev).
> - */
> - dev_null_fd = open ("/dev/null", O_RDONLY|O_CLOEXEC);
> - if (dev_null_fd == -1) {
> - reply_with_perror ("/dev/null");
> - return NULL;
> - }
> -
> if (bind_mount (&bind_state) == -1)
> return NULL;
> if (enable_network) {
> @@ -279,11 +268,9 @@ do_command (char *const *argv)
> return NULL;
> }
>
> - flags = COMMAND_FLAG_CHROOT_COPY_FILE_TO_STDIN | dev_null_fd;
> + flags = COMMAND_FLAG_DO_CHROOT;
>
> - CHROOT_IN;
> r = commandvf (&out, &err, flags, (const char * const *) argv);
> - CHROOT_OUT;
>
> free_bind_state (&bind_state);
> free_resolver_state (&resolver_state);
> diff --git a/daemon/daemon.h b/daemon/daemon.h
> index 7fbb2a2..af6f68c 100644
> --- a/daemon/daemon.h
> +++ b/daemon/daemon.h
> @@ -128,6 +128,7 @@ extern char **empty_list (void);
> #define COMMAND_FLAG_FD_MASK (1024-1)
> #define COMMAND_FLAG_FOLD_STDOUT_ON_STDERR 1024
> #define COMMAND_FLAG_CHROOT_COPY_FILE_TO_STDIN 2048
> +#define COMMAND_FLAG_DO_CHROOT 4096
>
Any eason for having this decimal? The standard thing is to use hex.
Mostly that the current code was using that style already.
> extern int commandf (char **stdoutput, char **stderror, int
flags,
> const char *name, ...) __attribute__((sentinel));
> diff --git a/daemon/guestfsd.c b/daemon/guestfsd.c
> index 0a29aa6..47245f7 100644
> --- a/daemon/guestfsd.c
> +++ b/daemon/guestfsd.c
> @@ -932,21 +932,44 @@ commandrvf (char **stdoutput, char **stderror, int flags,
> signal (SIGPIPE, SIG_DFL);
> close (0);
> if (flag_copy_stdin) {
> - dup2 (flag_copy_fd, STDIN_FILENO);
> + if (dup2 (flag_copy_fd, STDIN_FILENO) == -1) {
> + perror ("dup2/flag_copy_fd");
> + _exit (EXIT_FAILURE);
> + }
close(0) explicitly assumes that stdin is 0, which is fine, but dup2
uses STDIN_FILENO (which itself is also fine), but you should stick to
one scheme.
Like in the case above, this is what the code before was doing.
I could change it, but in a later patch, as I want to avoid mixing style
and functional changes in the same patch.
> ignore_value (chdir ("/"));
>
This could also be error-checked.
Indeed, fixed locally:
+ if (chdir ("/") == -1) {
+ perror ("chdir");
+ _exit (EXIT_FAILURE);
+ }
Thanks for review,
--
Pino Toscano