linux-kernel - [PATCH v2 1/7] kdb: Fix buffer overflow during tab-complete

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20240422-kgdb_read_refactor-v2-1-ed51f7d145fe@linaro.org>
Date: Mon, 22 Apr 2024 17:35:54 +0100
From: Daniel Thompson <daniel.thompson@...aro.org>
To: Jason Wessel <jason.wessel@...driver.com>, 
 Douglas Anderson <dianders@...omium.org>
Cc: kgdb-bugreport@...ts.sourceforge.net, linux-kernel@...r.kernel.org, 
 Daniel Thompson <daniel.thompson@...aro.org>, 
 Justin Stitt <justinstitt@...gle.com>, stable@...r.kernel.org
Subject: [PATCH v2 1/7] kdb: Fix buffer overflow during tab-complete

Currently, when the user attempts symbol completion with the Tab key, kdb
will use strncpy() to insert the completed symbol into the command buffer.
Unfortunately it passes the size of the source buffer rather than the
destination to strncpy() with predictably horrible results. Most obviously
if the command buffer is already full but cp, the cursor position, is in
the middle of the buffer, then we will write past the end of the supplied
buffer.

Fix this by replacing the dubious strncpy() calls with memmove()/memcpy()
calls plus explicit boundary checks to make sure we have enough space
before we start moving characters around.

Reported-by: Justin Stitt <justinstitt@...gle.com>
Closes: https://lore.kernel.org/all/CAFhGd8qESuuifuHsNjFPR-Va3P80bxrw+LqvC8deA8GziUJLpw@mail.gmail.com/
Cc: stable@...r.kernel.org
Signed-off-by: Daniel Thompson <daniel.thompson@...aro.org>
---
 kernel/debug/kdb/kdb_io.c | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c
index 9443bc63c5a24..06dfbccb10336 100644
--- a/kernel/debug/kdb/kdb_io.c
+++ b/kernel/debug/kdb/kdb_io.c
@@ -367,14 +367,19 @@ static char *kdb_read(char *buffer, size_t bufsize)
 			kdb_printf(kdb_prompt_str);
 			kdb_printf("%s", buffer);
 		} else if (tab != 2 && count > 0) {
-			len_tmp = strlen(p_tmp);
-			strncpy(p_tmp+len_tmp, cp, lastchar-cp+1);
-			len_tmp = strlen(p_tmp);
-			strncpy(cp, p_tmp+len, len_tmp-len + 1);
-			len = len_tmp - len;
-			kdb_printf("%s", cp);
-			cp += len;
-			lastchar += len;
+			/* How many new characters do we want from tmpbuffer? */
+			len_tmp = strlen(p_tmp) - len;
+			if (lastchar + len_tmp >= bufend)
+				len_tmp = bufend - lastchar;
+
+			if (len_tmp) {
+				/* + 1 ensures the '\0' is memmove'd */
+				memmove(cp+len_tmp, cp, (lastchar-cp) + 1);
+				memcpy(cp, p_tmp+len, len_tmp);
+				kdb_printf("%s", cp);
+				cp += len_tmp;
+				lastchar += len_tmp;
+			}
 		}
 		kdb_nextline = 1; /* reset output line number */
 		break;

-- 
2.43.0