在 2022/5/19 3:17, Kees Cook 写道:
WARNON(path_noexec(&file->f_path)) // path_noexec() checks fail
Did you encounter this in the real world?
I found the problem by running fuzz test.(syzkaller)
Here is a brief reproducer.
1. Apply diff
2. Complie and run repo.c
diff
diff --git a/fs/exec.c b/fs/exec.c
index e3e55d5e0be1..388d38b87e9a 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -897,6 +897,7 @@ EXPORT_SYMBOL(transfer_args_to_stack);
#endif /* CONFIG_MMU */
+#include <linux/delay.h>
static struct file *do_open_execat(int fd, struct filename *name, int
flags)
{
struct file *file;
@@ -925,9 +926,15 @@ static struct file *do_open_execat(int fd, struct
filename *name, int flags)
* and check again at the very end too.
*/
err = -EACCES;
+ if (!strcmp(file->f_path.dentry->d_iname, "my_bin")) {
+ pr_err("wait ...\n");
+ msleep(3000);
+ }
if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode) ||
- path_noexec(&file->f_path)))
+ path_noexec(&file->f_path))) {
+ pr_err("exec %pd %d %d %s\n", file->f_path.dentry,
file->f_path.mnt->mnt_flags & MNT_NOEXEC,
file->f_path.mnt->mnt_sb->s_iflags & SB_I_NOEXEC,
file->f_path.mnt->mnt_sb->s_type->name);
goto exit;
+ }
err = deny_write_access(file);
if (err)
repo.c
int main(void)
{
int ret;
system("umount temp 2>&1 > /dev/null");
system("mount -t tmpfs none temp");
system("echo 12312 > temp/my_bin && chmod +x temp/my_bin");
ret = fork();
if (ret < 0) {
perror("fork fail");
return 0;
}
if (ret == 0) {
system("mount -oremount,noexec temp");
exit(0);
} else {
execve("/root/temp/my_bin", NULL, 0);
//syscall(__NR_uselib, "/root/temp/my_bin");
}
return 0;
}
You're saying this is a race condition? A concurrent remount causes
this warning?
It seems not an unreasonable thing to warn about. Perhaps since it's
technically reachable from userspace, it could be downgraded to
pr_warn(), but I certainly don't want to remove the checks.
I'd like to leave this as-is, since we _do_ want to find the cases where
we're about to allow an exec and a very important security check was NOT
handled.
I think removing redundant checking is okay,
do_open_execat/uselib has initialized the acc_mode and open_flag for
exec file, the check is equivalent to check in may_open().
Remount(noexec) operations can alos happen after the latest check,
double check has no means for the concurrent situation.
The MNT_NOEXEC flag only affects the open operation, it won't cause any
problems that an opened bin file is executing in a non-exec mounted
filesystem.
