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kdb: Fix buffer overflow during tab-complete

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commit e9730744bf upstream.

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@google.com>
Closes: https://lore.kernel.org/all/CAFhGd8qESuuifuHsNjFPR-Va3P80bxrw+LqvC8deA8GziUJLpw@mail.gmail.com/
Cc: stable@vger.kernel.org
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Justin Stitt <justinstitt@google.com>
Tested-by: Justin Stitt <justinstitt@google.com>
Link: https://lore.kernel.org/r/20240424-kgdb_read_refactor-v3-1-f236dbe9828d@linaro.org
Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Daniel Thompson 2024-04-24 15:03:34 +01:00 committed by Greg Kroah-Hartman
parent 6da1ffc4bc
commit 33d9c81465
1 changed files with 13 additions and 8 deletions
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21
kernel/debug/kdb/kdb_io.c
View file

@ -353,14 +353,19 @@ 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;