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From:   Arnd Bergmann <arnd@kernel.org>
To:     Thierry Reding <thierry.reding@gmail.com>,
        Jonathan Hunter <jonathanh@nvidia.com>
Cc:     Arvind Sankar <nivedita@alum.mit.edu>,
        Arnd Bergmann <arnd@arndb.de>,
        Thierry Reding <treding@nvidia.com>,
        Timo Alho <talho@nvidia.com>, linux-tegra@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: [PATCH] [v2] firmware: tegra: fix strncpy()/strncat() confusion
Date:   Mon, 26 Oct 2020 17:49:21 +0100
Message-Id: <20201026164937.3722420-1-arnd@kernel.org>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

From: Arnd Bergmann <arnd@arndb.de>

The way that bpmp_populate_debugfs_inband() uses strncpy()
and strncat() makes no sense since the size argument for
the first is insufficient to contain the trailing '/'
and the second passes the length of the input rather than
the output, which triggers a warning:

In function 'strncat',
    inlined from 'bpmp_populate_debugfs_inband' at ../drivers/firmware/tegra/bpmp-debugfs.c:422:4:
include/linux/string.h:289:30: warning: '__builtin_strncat' specified bound depends on the length of the source argument [-Wstringop-overflow=]
  289 | #define __underlying_strncat __builtin_strncat
      |                              ^
include/linux/string.h:367:10: note: in expansion of macro '__underlying_strncat'
  367 |   return __underlying_strncat(p, q, count);
      |          ^~~~~~~~~~~~~~~~~~~~
drivers/firmware/tegra/bpmp-debugfs.c: In function 'bpmp_populate_debugfs_inband':
include/linux/string.h:288:29: note: length computed here
  288 | #define __underlying_strlen __builtin_strlen
      |                             ^
include/linux/string.h:321:10: note: in expansion of macro '__underlying_strlen'
  321 |   return __underlying_strlen(p);

Simplify this to use an snprintf() instead.

Fixes: 5e37b9c137ee ("firmware: tegra: Add support for in-band debug")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
v2: Use the correct arguments for snprintf(), as pointed out by Arvind Sankar
---
 drivers/firmware/tegra/bpmp-debugfs.c | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/drivers/firmware/tegra/bpmp-debugfs.c b/drivers/firmware/tegra/bpmp-debugfs.c
index c1bbba9ee93a..440d99c63638 100644
--- a/drivers/firmware/tegra/bpmp-debugfs.c
+++ b/drivers/firmware/tegra/bpmp-debugfs.c
@@ -412,16 +412,12 @@ static int bpmp_populate_debugfs_inband(struct tegra_bpmp *bpmp,
 				goto out;
 			}
 
-			len = strlen(ppath) + strlen(name) + 1;
+			len = snprintf(pathbuf, pathlen, "%s%s/", ppath, name);
 			if (len >= pathlen) {
 				err = -EINVAL;
 				goto out;
 			}
 
-			strncpy(pathbuf, ppath, pathlen);
-			strncat(pathbuf, name, strlen(name));
-			strcat(pathbuf, "/");
-
 			err = bpmp_populate_debugfs_inband(bpmp, dentry,
 							   pathbuf);
 			if (err < 0)
-- 
2.27.0