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>
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@ -398,6 +398,13 @@ int kdb_set(int argc, const char **argv)
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if (argc != 2)
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return KDB_ARGCOUNT;
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/*
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* Censor sensitive variables
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*/
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if (strcmp(argv[1], "PROMPT") == 0 &&
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!kdb_check_flags(KDB_ENABLE_MEM_READ, kdb_cmd_enabled, false))
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return KDB_NOPERM;
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/*
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* Check for internal variables
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*/
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@ -1298,12 +1305,9 @@ static int kdb_local(kdb_reason_t reason, int error, struct pt_regs *regs,
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*(cmd_hist[cmd_head]) = '\0';
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do_full_getstr:
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#if defined(CONFIG_SMP)
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/* PROMPT can only be set if we have MEM_READ permission. */
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snprintf(kdb_prompt_str, CMD_BUFLEN, kdbgetenv("PROMPT"),
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raw_smp_processor_id());
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#else
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snprintf(kdb_prompt_str, CMD_BUFLEN, kdbgetenv("PROMPT"));
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#endif
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if (defcmd_in_progress)
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strncat(kdb_prompt_str, "[defcmd]", CMD_BUFLEN);
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