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kdb: Censor attempts to set PROMPT without ENABLE_MEM_READ

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[ Upstream commit ad99b5105c0823ff02126497f4366e6a8009453e ]

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>
Stable-dep-of: 4f41d30cd6dc ("kdb: Fix a potential buffer overflow in kdb_local()")
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Daniel Thompson 2020-02-13 15:16:40 +00:00 committed by Greg Kroah-Hartman
parent 36b6db699c
commit cf6260a34d
1 changed files with 8 additions and 4 deletions
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12
kernel/debug/kdb/kdb_main.c
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@ -452,6 +452,13 @@ 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
*/
@ -1355,12 +1362,9 @@ 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);