Messages in this thread | | | Date | Wed, 19 Apr 2017 16:38:22 +0000 | From | "Naveen N. Rao" <> | Subject | Re: [PATCH v3 3/7] kprobes: validate the symbol name length |
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Excerpts from Masami Hiramatsu's message of April 19, 2017 20:07: > On Wed, 19 Apr 2017 18:21:02 +0530 > "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> wrote: > >> When a kprobe is being registered, we use the symbol_name field to >> lookup the address where the probe should be placed. Since this is a >> user-provided field, let's ensure that the length of the string is >> within expected limits. > > Would we really need this? Of course it may filter out longer > strings... anyway such name should be rejected by kallsyms.
I felt this would be good to have generically, as kallsyms does many string operations on the symbol name, including an unbounded strchr().
> > [...] >> diff --git a/kernel/kprobes.c b/kernel/kprobes.c >> index 6a128f3a7ed1..bb86681c8a10 100644 >> --- a/kernel/kprobes.c >> +++ b/kernel/kprobes.c >> @@ -1382,6 +1382,28 @@ bool within_kprobe_blacklist(unsigned long addr) >> return false; >> } >> >> +bool is_valid_kprobe_symbol_name(const char *name) > > This just check the length of symbol_name buffer, and can contain > some invalid chars.
Yes, I kept the function name generic incase we would like to do more validation in future, plus it's shorter than is_valid_kprobe_symbol_name_len() ;-)
> >> +{ >> + size_t sym_len; >> + char *s; >> + >> + s = strchr(name, ':');
Hmm.. this should be strnchr(). I re-factored the code that moved the strnlen() above this below. I'll fix this.
>> + if (s) { >> + sym_len = strnlen(s+1, KSYM_NAME_LEN); > > If you use strnlen() here, you just need to ensure sym_len < KSYM_NAME_LEN.
Hmm.. not sure I follow. Are you saying the check for sym_len <= 0 is not needed?
> >> + if (sym_len <= 0 || sym_len >= KSYM_NAME_LEN) >> + return false; >> + sym_len = (size_t)(s - name); >> + if (sym_len <= 0 || sym_len >= MODULE_NAME_LEN) >> + return false; >> + } else { >> + sym_len = strnlen(name, MODULE_NAME_LEN); >> + if (sym_len <= 0 || sym_len >= MODULE_NAME_LEN) > > Would you mean KSYM_NAME_LEN here?
Oops... nice catch, Thanks!
- Naveen
> >> + return false; >> + } >> + >> + return true; >> +} >> + >> /* >> * If we have a symbol_name argument, look it up and add the offset field >> * to it. This way, we can specify a relative address to a symbol. >> @@ -1397,6 +1419,8 @@ static kprobe_opcode_t *kprobe_addr(struct kprobe *p) >> goto invalid; >> >> if (p->symbol_name) { >> + if (!is_valid_kprobe_symbol_name(p->symbol_name)) >> + return ERR_PTR(-EINVAL); >> addr = kprobe_lookup_name(p->symbol_name, p->offset); >> if (!addr) >> return ERR_PTR(-ENOENT); >> diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c >> index 5f688cc724f0..bf73e5f31128 100644 >> --- a/kernel/trace/trace_kprobe.c >> +++ b/kernel/trace/trace_kprobe.c >> @@ -704,6 +704,10 @@ static int create_trace_kprobe(int argc, char **argv) >> pr_info("Return probe must be used without offset.\n"); >> return -EINVAL; >> } >> + if (!is_valid_kprobe_symbol_name(symbol)) { >> + pr_info("Symbol name is too long.\n"); >> + return -EINVAL; >> + } >> } >> argc -= 2; argv += 2; >> >> -- >> 2.12.1 >> > > Thanks, > > -- > Masami Hiramatsu <mhiramat@kernel.org> > >
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