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ftrace: Initialize modname and offset in print_rec()

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print_rec() leaves 'modname' and 'offset' uninitialized and
kallsyms_lookup() only sets them on success. When the lookup fails like
when a module is being loaded or unloaded, 'modname' holds a garbage
value, passes the 'if (modname)' check, and is dereferenced by
seq_printf().

  Oops: general protection fault
  RIP: 0010:string+0x48/0xe0
  Call Trace:
   vsnprintf+0x1f5/0x650
   seq_printf+0x8e/0xb0
   print_rec+0x6c/0xc0
   t_show+0x4c/0x440
   seq_read_iter+0x119/0x480

This can be triggered by reading available_filter_functions while a
module is being loaded or unloaded.

Initialize both variables so a failed lookup skips the module name.

Cc: stable@vger.kernel.org
Fixes: b39181f7c6 ("ftrace: Add FTRACE_MCOUNT_MAX_OFFSET to avoid adding weak function")
Link: https://patch.msgid.link/20261016230403.4916-1-aarnahmd@amazon.com
Tested-by: Gavin Inglis <giinglis@amazon.com>
Signed-off-by: Aaron Ahmed <aarnahmd@amazon.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
Aaron Ahmed 2026-10-16 23:04:03 +00:00 committed by Steven Rostedt
parent c738829502
commit e1f339ff3b
1 changed files with 2 additions and 2 deletions
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4
kernel/trace/ftrace.c
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@ -4431,9 +4431,9 @@ subsys_initcall(ftrace_check_for_weak_functions);
static int print_rec(struct seq_file *m, unsigned long ip)
{
unsigned long offset;
unsigned long offset = 0;
char str[KSYM_SYMBOL_LEN];
char *modname;
char *modname = NULL;
const char *ret;
ret = kallsyms_lookup(ip, NULL, &offset, &modname, str);