Stefan Hajnoczi ebf101955c virtiofsd: avoid /proc/self/fd tempdir ... In order to prevent /proc/self/fd escapes a temporary directory is created where /proc/self/fd is bind-mounted. This doesn't work on read-only file systems. Avoid the temporary directory by bind-mounting /proc/self/fd over /proc. This does not affect other processes since we remounted / with MS_REC | MS_SLAVE. /proc must exist and virtiofsd does not use it so it's safe to do this. Path traversal can be tested with the following function: static void test_proc_fd_escape(struct lo_data *lo) { int fd; int level = 0; ino_t last_ino = 0; fd = lo->proc_self_fd; for (;;) { struct stat st; if (fstat(fd, &st) != 0) { perror("fstat"); return; } if (last_ino && st.st_ino == last_ino) { fprintf(stderr, "inode number unchanged, stopping\n"); return; } last_ino = st.st_ino; fprintf(stderr, "Level %d dev %lu ino %lu\n", level, (unsigned long)st.st_dev, (unsigned long)last_ino); fd = openat(fd, "..", O_PATH | O_DIRECTORY | O_NOFOLLOW); level++; } } Before and after this patch only Level 0 is displayed. Without /proc/self/fd bind-mount protection it is possible to traverse parent directories. Fixes: 397ae982f4 ("virtiofsd: jail lo->proc_self_fd") Cc: Miklos Szeredi <mszeredi@redhat.com> Cc: Jens Freimann <jfreimann@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> Message-Id: <20201006095826.59813-1-stefanha@redhat.com> Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com> Tested-by: Jens Freimann <jfreimann@redhat.com> Reviewed-by: Jens Freimann <jfreimann@redhat.com> Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>		2020-10-12 12:39:38 +01:00
..
virtiofsd	virtiofsd: avoid /proc/self/fd tempdir	2020-10-12 12:39:38 +01:00
meson.build	tools/virtiofsd: convert to Meson	2020-08-21 06:30:09 -04:00