Re: [PATCH 2/2] libkmod-builtin: consider final NIL in name length check

On Wed, Jun 09, 2021 at 10:10:53AM -0700, Lucas De Marchi wrote:

On Tue, Jun 08, 2021 at 09:29:23AM +0300, Yauheni Kaliuta wrote:

quoted

There is potential buffer overrun in kmod_builtin_iter_get_modname()
for the name of length PATH_MAX. The required buffer size is
PATH_MAX, so `modname[len] = '\0'` with len == PATH_MAX will write
right beyond the buffer.

this doesn't look correct. "with len == PATH_MAX" we will actually
return an error.

What indeed is happening is truncation: since we are not reserving 1
char for NUL termination, we will truncate the name. If we update the
commit message to state the right reasoning, then we can land this patch.

I don't see any buffer overflow here, but I may be missing something.

another thing... what is your git-sendemail setup? This is putting patch
2 as a reply to patch 1 and that breaks b4. See:
https://lore.kernel.org/linux-modules/20210608062923.94017-1-ykaliuta@redhat.com/T/#u (local)

Lucas De Marchi

thanks
LUcas De Marchi

quoted

Check the length against PATH_MAX - 1.

Signed-off-by: Yauheni Kaliuta <redacted>
---
libkmod/libkmod-builtin.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libkmod/libkmod-builtin.c b/libkmod/libkmod-builtin.c
index a002cb5ee2c6..3d4d77ab29b3 100644
--- a/libkmod/libkmod-builtin.c
+++ b/libkmod/libkmod-builtin.c

@@ -246,7 +246,7 @@ bool kmod_builtin_iter_get_modname(struct kmod_builtin_iter *iter,

len = dot - line;

-	if (len >= PATH_MAX) {
+	if (len >= PATH_MAX - 1) {
	sv_errno = ENAMETOOLONG;
	goto fail;
}
-- 
2.31.1