From ad99b5105c0823ff02126497f4366e6a8009453e Mon Sep 17 00:00:00 2001 From: Daniel Thompson Date: Thu, 13 Feb 2020 15:16:40 +0000 Subject: [PATCH] kdb: Censor attempts to set PROMPT without ENABLE_MEM_READ Currently the PROMPT variable could be abused to provoke the printf() machinery to read outside the current stack frame. Normally this doesn't matter becaues md is already a much better tool for reading from memory. However the md command can be disabled by not setting KDB_ENABLE_MEM_READ. Let's also prevent PROMPT from being modified in these circumstances. Whilst adding a comment to help future code reviewers we also remove the #ifdef where PROMPT in consumed. There is no problem passing an unused (0) to snprintf when !CONFIG_SMP. argument Reported-by: Wang Xiayang Signed-off-by: Daniel Thompson Reviewed-by: Douglas Anderson --- kernel/debug/kdb/kdb_main.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-) diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c index a4641be..515379c 100644 --- a/kernel/debug/kdb/kdb_main.c +++ b/kernel/debug/kdb/kdb_main.c @@ -399,6 +399,13 @@ int kdb_set(int argc, const char **argv) return KDB_ARGCOUNT; /* + * Censor sensitive variables + */ + if (strcmp(argv[1], "PROMPT") == 0 && + !kdb_check_flags(KDB_ENABLE_MEM_READ, kdb_cmd_enabled, false)) + return KDB_NOPERM; + + /* * Check for internal variables */ if (strcmp(argv[1], "KDBDEBUG") == 0) { @@ -1298,12 +1305,9 @@ static int kdb_local(kdb_reason_t reason, int error, struct pt_regs *regs, *(cmd_hist[cmd_head]) = '\0'; do_full_getstr: -#if defined(CONFIG_SMP) + /* PROMPT can only be set if we have MEM_READ permission. */ snprintf(kdb_prompt_str, CMD_BUFLEN, kdbgetenv("PROMPT"), raw_smp_processor_id()); -#else - snprintf(kdb_prompt_str, CMD_BUFLEN, kdbgetenv("PROMPT")); -#endif if (defcmd_in_progress) strncat(kdb_prompt_str, "[defcmd]", CMD_BUFLEN); -- 2.7.4