From: Daniel Thompson <daniel.thompson@xxxxxxxxxx> commit e9730744bf3af04cda23799029342aa3cddbc454 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@xxxxxxxxxx> Closes: https://lore.kernel.org/all/CAFhGd8qESuuifuHsNjFPR-Va3P80bxrw+LqvC8deA8GziUJLpw@xxxxxxxxxxxxxx/ Cc: stable@xxxxxxxxxxxxxxx Reviewed-by: Douglas Anderson <dianders@xxxxxxxxxxxx> Reviewed-by: Justin Stitt <justinstitt@xxxxxxxxxx> Tested-by: Justin Stitt <justinstitt@xxxxxxxxxx> Link: https://lore.kernel.org/r/20240424-kgdb_read_refactor-v3-1-f236dbe9828d@xxxxxxxxxx Signed-off-by: Daniel Thompson <daniel.thompson@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- kernel/debug/kdb/kdb_io.c | 21 +++++++++++++-------- 1 file changed, 13 insertions(+), 8 deletions(-) --- a/kernel/debug/kdb/kdb_io.c +++ b/kernel/debug/kdb/kdb_io.c @@ -364,14 +364,19 @@ poll_again: 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; Patches currently in stable-queue which might be from daniel.thompson@xxxxxxxxxx are queue-4.19/kdb-fix-console-handling-when-editing-and-tab-completing-commands.patch queue-4.19/kdb-use-format-specifiers-rather-than-memset-for-padding-in-kdb_read.patch queue-4.19/kdb-fix-buffer-overflow-during-tab-complete.patch queue-4.19/kdb-use-format-strings-rather-than-0-injection-in-kdb_read.patch queue-4.19/kdb-merge-identical-case-statements-in-kdb_read.patch
