[PATCH AUTOSEL 6.7 063/108] block/rnbd-srv: Check for unlikely string overflow

Sasha Levin
2024-01-16T19:45:22Z

From: Kees Cook <keescook@chromium.org>

[ Upstream commit 9e4bf6a08d1e127bcc4bd72557f2dfafc6bc7f41 ]

Since "dev_search_path" can technically be as large as PATH_MAX,
there was a risk of truncation when copying it and a second string
into "full_path" since it was also PATH_MAX sized. The W=1 builds were
reporting this warning:

drivers/block/rnbd/rnbd-srv.c: In function 'process_msg_open.isra':
drivers/block/rnbd/rnbd-srv.c:616:51: warning: '%s' directive output may be truncated writing up to 254 bytes into a region of size between 0 and 4095 [-Wformat-truncation=]
616 | snprintf(full_path, PATH_MAX, "%s/%s",
| ^~
In function 'rnbd_srv_get_full_path',
inlined from 'process_msg_open.isra' at drivers/block/rnbd/rnbd-srv.c:721:14: drivers/block/rnbd/rnbd-srv.c:616:17: note: 'snprintf' output between 2 and 4351 bytes into a destination of size 4096
616 | snprintf(full_path, PATH_MAX, "%s/%s",
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
617 | dev_search_path, dev_name);
| ~~~~~~~~~~~~~~~~~~~~~~~~~~

To fix this, unconditionally check for truncation (as was already done
for the case where "%SESSNAME%" was present).

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202312100355.lHoJPgKy-lkp@intel.com/
Cc: Md. Haris Iqbal <haris.iqbal@ionos.com>
Cc: Jack Wang <jinpu.wang@ionos.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: <linux-block@vger.kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Guoqing Jiang <guoqing.jiang@linux.dev>
Acked-by: Jack Wang <jinpu.wang@ionos.com>
Link: https://lore.kernel.org/r/20231212214738.work.169-kees@kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/block/rnbd/rnbd-srv.c | 19 ++++++++++---------
1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/drivers/block/rnbd/rnbd-srv.c b/drivers/block/rnbd/rnbd-srv.c
index 65de51f3dfd9..ab78eab97d98 100644
--- a/drivers/block/rnbd/rnbd-srv.c
+++ b/drivers/block/rnbd/rnbd-srv.c
@@ -585,6 +585,7 @@ static char *rnbd_srv_get_full_path(struct rnbd_srv_session *srv_sess,
{
char *full_path;
char *a, *b;
+ int len;

full_path = kmalloc(PATH_MAX, GFP_KERNEL);
if (!full_path)
@@ -596,19 +597,19 @@ static char *rnbd_srv_get_full_path(struct rnbd_srv_session *srv_sess,
*/
a = strnstr(dev_search_path, "%SESSNAME%", sizeof(dev_search_path));
if (a) {
- int len = a - dev_search_path;
+ len = a - dev_search_path;

len = snprintf(full_path, PATH_MAX, "%.*s/%s/%s", len,
dev_search_path, srv_sess->sessname, dev_name);
- if (len >= PATH_MAX) {
- pr_err("Too long path: %s, %s, %s\n",
- dev_search_path, srv_sess->sessname, dev_name);
- kfree(full_path);
- return ERR_PTR(-EINVAL);
- }
} else {
- snprintf(full_path, PATH_MAX, "%s/%s",
- dev_search_path, dev_name);
+ len = snprintf(full_path, PATH_MAX, "%s/%s",
+ dev_search_path, dev_name);
+ }
+ if (len >= PATH_MAX) {
+ pr_err("Too long path: %s, %s, %s\n",
+ dev_search_path, srv_sess->sessname, dev_name);
+ kfree(full_path);
+ return ERR_PTR(-EINVAL);
}

/* eliminitate duplicated slashes */
--
2.43.0