Commit ad99b510 authored Feb 13, 2020 by Daniel Thompson

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 <xywang.sjtu@sjtu.edu.cn>
Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>

parent d228bee8

kernel/debug/kdb/kdb_main.c

+8 −4

Original line number	Diff line number	Diff line
		@@ -398,6 +398,13 @@ int kdb_set(int argc, const char **argv)
		if (argc != 2)
		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
		*/
		@@ -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);

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