This is a note to let you know that I've just added the patch titled
kdb: Censor attempts to set PROMPT without ENABLE_MEM_READ
to the 4.19-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
kdb-censor-attempts-to-set-prompt-without-enable_mem.patch
and it can be found in the queue-4.19 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit cf437289504d229e7e6ba24ddadfd0d17fe734ff
Author: Daniel Thompson <daniel.thompson@xxxxxxxxxx>
Date: Thu Feb 13 15:16:40 2020 +0000
kdb: Censor attempts to set PROMPT without ENABLE_MEM_READ
[ 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@xxxxxxxxxxx>
Signed-off-by: Daniel Thompson <daniel.thompson@xxxxxxxxxx>
Reviewed-by: Douglas Anderson <dianders@xxxxxxxxxxxx>
Stable-dep-of: 4f41d30cd6dc ("kdb: Fix a potential buffer overflow in kdb_local()")
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c
index dc6bf35e7884..8f31d472384f 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)
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
*/
@@ -1299,12 +1306,9 @@ 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);
