> Will address it in v2.
>
> > If we're gonna do this, it makes sense to document the ELF note binary
> > limiations. Then, consider a defense too, what if a specially crafted
> > binary with a huge elf note are core dumped many times, what then?
> > Lifting to 4 MiB puts in a situation where abuse can lead to many silly
> > insane kvmalloc()s. Is that what we want? Why?
> >
> You raise a good point. I need to see how we can safely handle this case.
>
Luis,
Here's a rough idea that caps the max allowable size for the note section.
I am using 16MB as the max value.
--- a/fs/coredump.c
+++ b/fs/coredump.c
@@ -56,10 +56,14 @@
static bool dump_vma_snapshot(struct coredump_params *cprm);
static void free_vma_snapshot(struct coredump_params *cprm);
+#define MAX_FILE_NOTE_SIZE (4*1024*1024)
+#define MAX_ALLOWED_NOTE_SIZE (16*1024*1024)
+
static int core_uses_pid;
static unsigned int core_pipe_limit;
static char core_pattern[CORENAME_MAX_SIZE] = "core";
static int core_name_size = CORENAME_MAX_SIZE;
+unsigned int core_file_note_size_max = MAX_FILE_NOTE_SIZE;
struct core_name {
char *corename;
@@ -1060,12 +1064,22 @@ static struct ctl_table coredump_sysctls[] = {
.mode = 0644,
.proc_handler = proc_dointvec,
},
+ {
+ .procname = "core_file_note_size_max",
+ .data = &core_file_note_size_max,
+ .maxlen = sizeof(unsigned int),
+ .mode = 0644,
+ .proc_handler = proc_core_file_note_size_max,
+ },
};
+int proc_core_file_note_size_max(struct ctl_table *table, int write,
void __user *buffer, size_t *lenp, loff_t *ppos) {
+ int error = proc_douintvec(table, write, buffer, lenp, ppos);
+ if (write && (core_file_note_size_max < MAX_FILE_NOTE_SIZE
+ || core_file_note_size_max > MAX_ALLOWED_NOTE_SIZE))
+. /* Revert to default if out of bounds */
+ core_file_note_size_max = MAX_FILE_NOTE_SIZE;
+ return error;
+}
Let me know what you think.
Thanks,
- Allen
