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pasta, util: Align stack area for clones to maximum natural alignment 

Given that we use this stack pointer as a location to store arbitrary
data types from the cloned process, we need to guarantee that its
alignment matches any of those possible data types.

runsisi reports that pasta gets a SIGBUS in pasta_open_ns() on
aarch64, where the alignment requirement for stack pointers is a
16 bytes (same as the size of a long double), and similar requirements
actually apply to most architectures we run on.

Reported-by: runsisi <runsisi@hust.edu.cn>
Link: https://bugs.passt.top/show_bug.cgi?id=85
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
This commit is contained in:
Stefano Brivio 2024-04-11 17:48:23 +02:00
parent 5d5208b67d
commit ee338a256e
2 changed files with 5 additions and 2 deletions
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3
pasta.c
View File

@ -211,12 +211,13 @@ static int pasta_spawn_cmd(void *arg)
void pasta_start_ns(struct ctx *c, uid_t uid, gid_t gid,
int argc, char *argv[])
{
char ns_fn_stack[NS_FN_STACK_SIZE]
__attribute__ ((aligned(__alignof__(max_align_t))));
struct pasta_spawn_cmd_arg arg = {
.exe = argv[0],
.argv = argv,
};
char uidmap[BUFSIZ], gidmap[BUFSIZ];
char ns_fn_stack[NS_FN_STACK_SIZE];
char *sh_argv[] = { NULL, NULL };
char sh_arg0[PATH_MAX + 1];
sigset_t set;

4
util.h
View File

@ -9,6 +9,7 @@
#include <stdlib.h>
#include <stdarg.h>
#include <stdbool.h>
#include <stddef.h>
#include <string.h>
#include <signal.h>
@ -116,7 +117,8 @@ int do_clone(int (*fn)(void *), char *stack_area, size_t stack_size, int flags,
void *arg);
#define NS_CALL(fn, arg) \
do { \
char ns_fn_stack[NS_FN_STACK_SIZE]; \
char ns_fn_stack[NS_FN_STACK_SIZE] \
__attribute__ ((aligned(__alignof__(max_align_t)))); \
\
do_clone((fn), ns_fn_stack, sizeof(ns_fn_stack), \
CLONE_VM | CLONE_VFORK | CLONE_FILES | SIGCHLD,\