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[35.188.70.54]) by smtp.gmail.com with ESMTPSA id x1-20020a5d9ac1000000b00760f535cd5asm3103481ion.10.2023.05.09.15.30.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 09 May 2023 15:30:39 -0700 (PDT) From: Azeem Shaikh To: Greg Kroah-Hartman , Tejun Heo Cc: security@kernel.org, Azeem Shaikh , linux-kernel@vger.kernel.org Subject: kernfs: Prefer strscpy over strlcpy calls Date: Tue, 9 May 2023 22:30:36 +0000 Message-ID: <20230509223036.3007500-1-azeemshaikh38@gmail.com> X-Mailer: git-send-email 2.40.1.521.gf1e218fcd8-goog MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" strlcpy() reads the entire source buffer first. This read may exceed the destination size limit. This is both inefficient and can lead to linear read overflows if a source string is not NUL-terminated. Since strscpy() returns -E2BIG on truncate, we rely on strlen(src) to imitate strlcpy behavior. Signed-off-by: Azeem Shaikh --- fs/kernfs/dir.c | 23 +++++++++++++++-------- 1 file changed, 15 insertions(+), 8 deletions(-) diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c index 45b6919903e6..0f46d7b304b0 100644 --- a/fs/kernfs/dir.c +++ b/fs/kernfs/dir.c @@ -51,12 +51,19 @@ static bool kernfs_lockdep(struct kernfs_node *kn) #endif } =20 +/* strscpy_mock_strlcpy - imitates strlcpy API but uses strscpy underneath= . */ +static size_t strscpy_mock_strlcpy(char *dest, const char *src, size_t cou= nt) +{ + strscpy(dest, src, count); + return strlen(src); +} + static int kernfs_name_locked(struct kernfs_node *kn, char *buf, size_t bu= flen) { if (!kn) - return strlcpy(buf, "(null)", buflen); + return strscpy_mock_strlcpy(buf, "(null)", buflen); =20 - return strlcpy(buf, kn->parent ? kn->name : "/", buflen); + return strscpy_mock_strlcpy(buf, kn->parent ? kn->name : "/", buflen); } =20 /* kernfs_node_depth - compute depth from @from to @to */ @@ -141,13 +148,13 @@ static int kernfs_path_from_node_locked(struct kernfs= _node *kn_to, int i, j; =20 if (!kn_to) - return strlcpy(buf, "(null)", buflen); + return strscpy_mock_strlcpy(buf, "(null)", buflen); =20 if (!kn_from) kn_from =3D kernfs_root(kn_to)->kn; =20 if (kn_from =3D=3D kn_to) - return strlcpy(buf, "/", buflen); + return strscpy_mock_strlcpy(buf, "/", buflen); =20 common =3D kernfs_common_ancestor(kn_from, kn_to); if (WARN_ON(!common)) @@ -159,16 +166,16 @@ static int kernfs_path_from_node_locked(struct kernfs= _node *kn_to, buf[0] =3D '\0'; =20 for (i =3D 0; i < depth_from; i++) - len +=3D strlcpy(buf + len, parent_str, + len +=3D strscpy_mock_strlcpy(buf + len, parent_str, len < buflen ? buflen - len : 0); =20 /* Calculate how many bytes we need for the rest */ for (i =3D depth_to - 1; i >=3D 0; i--) { for (kn =3D kn_to, j =3D 0; j < i; j++) kn =3D kn->parent; - len +=3D strlcpy(buf + len, "/", + len +=3D strscpy_mock_strlcpy(buf + len, "/", len < buflen ? buflen - len : 0); - len +=3D strlcpy(buf + len, kn->name, + len +=3D strscpy_mock_strlcpy(buf + len, kn->name, len < buflen ? buflen - len : 0); } =20 @@ -851,7 +858,7 @@ static struct kernfs_node *kernfs_walk_ns(struct kernfs= _node *parent, =20 spin_lock_irq(&kernfs_pr_cont_lock); =20 - len =3D strlcpy(kernfs_pr_cont_buf, path, sizeof(kernfs_pr_cont_buf)); + len =3D strscpy_mock_strlcpy(kernfs_pr_cont_buf, path, sizeof(kernfs_pr_c= ont_buf)); =20 if (len >=3D sizeof(kernfs_pr_cont_buf)) { spin_unlock_irq(&kernfs_pr_cont_lock); --=20 2.40.1.521.gf1e218fcd8-goog