linux-hardening - [PATCH v6] EDAC/mc: Prefer strscpy or scnprintf over strcpy

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Message-Id: <20210903150539.7282-1-len.baker@gmx.com>
Date:   Fri,  3 Sep 2021 17:05:39 +0200
From:   Len Baker <len.baker@....com>
To:     Borislav Petkov <bp@...en8.de>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Tony Luck <tony.luck@...el.com>,
        James Morse <james.morse@....com>,
        Robert Richter <rric@...nel.org>, Joe Perches <joe@...ches.com>
Cc:     Len Baker <len.baker@....com>,
        David Laight <David.Laight@...LAB.COM>,
        Kees Cook <keescook@...omium.org>,
        linux-hardening@...r.kernel.org, linux-edac@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v6] EDAC/mc: Prefer strscpy or scnprintf over strcpy

strcpy() performs no bounds checking on the destination buffer. This
could result in linear overflows beyond the end of the buffer, leading
to all kinds of misbehaviors. The safe replacement is strscpy() [1].

However, to simplify and clarify the code, to concatenate labels use
the scnprintf() function. This way it is not necessary to check the
return value of strscpy (-E2BIG if the parameter count is 0 or the src
was truncated) since the scnprintf returns always the number of chars
written into the buffer. This function returns always a nul-terminated
string even if it needs to be truncated.

The main reason behind this patch is to remove all the strcpy() uses
from the kernel with the purpose to clean up the proliferation of
str*cpy() functions. Later on, the next step will be remove all the
strcpy implementations [2].

[1] https://www.kernel.org/doc/html/latest/process/deprecated.html#strcpy
[2] https://github.com/KSPP/linux/issues/88

Co-developed-by: Joe Perches <joe@...ches.com>
Signed-off-by: Joe Perches <joe@...ches.com>
Signed-off-by: Len Baker <len.baker@....com>
---
Hi Joe,

I have added the "Co-developed-by: Joe Perches" tag to give you credit,
since all the code used in this patch relies heavily on your review
code snippets.

I hope there are no objections.

Thanks,
Len

Changelog v1 -> v2
- Use the strscpy() instead of scnprintf() to add labels and follow a
  code pattern more similar to the current one (advance "p" and
  decrement "left") (Robert Richter).

Changelog v2 -> v3
- Rename the "left" variable to "len" (Robert Richter).
- Use strlen(p) instead of strlen(OTHER_LABEL) to decrement "len" and
  increment "p" as otherwise "left" could underflow and p overflow
  (Robert Richter).

Changelog v3 -> v4
- Change the commit subject (Joe Perches).
- Fix broken logic (Robert Richter).
- Rebase against v5.14-rc5.

Changelog v4 -> v5
- Change the commit subject.
- Clarify why the change is being made by adding more info to the
  commit message (Borislav Petkov).
- Use scnprintf instead of strscpy (Joe Perches).
- Rebase against v5.14-rc7.

Changelog v5 -> v6
- Rebase against v5.14.
- Refactor the code to use a more common scnprintf mechanism (Joe
  Perches).

Previous versions:

v1
https://lore.kernel.org/linux-hardening/20210725162954.9861-1-len.baker@gmx.com/

v2
https://lore.kernel.org/linux-hardening/20210801143558.12674-1-len.baker@gmx.com/

v3
https://lore.kernel.org/linux-hardening/20210807155957.10069-1-len.baker@gmx.com/

v4
https://lore.kernel.org/linux-hardening/20210814075527.5999-1-len.baker@gmx.com/

v5
https://lore.kernel.org/linux-hardening/20210829161547.6069-1-len.baker@gmx.com/

 drivers/edac/edac_mc.c | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/drivers/edac/edac_mc.c b/drivers/edac/edac_mc.c
index f6d462d0be2d..97dff62970a5 100644
--- a/drivers/edac/edac_mc.c
+++ b/drivers/edac/edac_mc.c
@@ -1032,6 +1032,8 @@ void edac_mc_handle_error(const enum hw_event_mc_err_type type,
 	int i, n_labels = 0;
 	struct edac_raw_error_desc *e = &mci->error_desc;
 	bool any_memory = true;
+	const char *prefix = "";
+	int n = 0;

 	edac_dbg(3, "MC%d\n", mci->mc_idx);

@@ -1113,12 +1115,9 @@ void edac_mc_handle_error(const enum hw_event_mc_err_type type,
 			p = e->label;
 			*p = '\0';
 		} else {
-			if (p != e->label) {
-				strcpy(p, OTHER_LABEL);
-				p += strlen(OTHER_LABEL);
-			}
-			strcpy(p, dimm->label);
-			p += strlen(p);
+			n += scnprintf(e->label + n, sizeof(e->label) - n,
+				       "%s%s", prefix, dimm->label);
+			prefix = OTHER_LABEL;
 		}

 		/*
@@ -1140,9 +1139,9 @@ void edac_mc_handle_error(const enum hw_event_mc_err_type type,
 	}

 	if (any_memory)
-		strcpy(e->label, "any memory");
+		strscpy(e->label, "any memory", sizeof(e->label));
 	else if (!*e->label)
-		strcpy(e->label, "unknown memory");
+		strscpy(e->label, "unknown memory", sizeof(e->label));

 	edac_inc_csrow(e, row, chan);

--
2.25.1