[PATCH v3] cmdline: prevent out-of-bounds read in completion buffer

[Daniil Iskhakov <dish@amicon.ru>]

tmp_buf is populated by the completion callback and is not guaranteed
to be NUL-terminated.

The code already accounts for this when computing tmp_size with
strnlen(tmp_buf, sizeof(tmp_buf)). However, another loop in the same
path still walks tmp_buf until a NUL byte is found, without checking
the buffer limit.

If the callback writes a full-sized non-NUL-terminated string, the loop
may read past the end of tmp_buf.

Fix this by computing a bounded length for each completion choice before
printing it.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: af75078fece3 ("first public release")
Cc: stable@dpdk.org

Signed-off-by: Daniil Iskhakov <dish@amicon.ru>
---
v3:
- Reworked the choice-printing loop to use a bounded length.
- Fixed coding style issues in the diff.
- Rebased and regenerated the patch; v2 did not apply cleanly.

v2:
- Resent to dev@dpdk.org because v1 was accidentally sent only to
  maintainers.

Cc: sdl.dpdk@linuxtesting.org
Cc: rrv@amicon.ru
---
 lib/cmdline/cmdline_rdline.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lib/cmdline/cmdline_rdline.c b/lib/cmdline/cmdline_rdline.c
index 0a5a399b32..e1770f0a1d 100644
--- a/lib/cmdline/cmdline_rdline.c
+++ b/lib/cmdline/cmdline_rdline.c
@@ -444,8 +444,9 @@ rdline_char_in(struct rdline *rdl, char c)
 				/* choice */
 				rdline_puts(rdl, "\r\n");
 				while (ret) {
+					tmp_size = strnlen(tmp_buf, sizeof(tmp_buf));
 					rdl->write_char(rdl, ' ');
-					for (i=0 ; tmp_buf[i] ; i++)
+					for (i = 0; i < tmp_size; i++)
 						rdl->write_char(rdl, tmp_buf[i]);
 					rdline_puts(rdl, "\r\n");
 					ret = rdl->complete(rdl, rdl->left_buf,
-- 
2.43.0