of: module: prevent NULL pointer dereference in vsnprintf()

commit a1aa5390cc912934fee76ce80af5f940452fa987 upstream.

In of_modalias(), we can get passed the str and len parameters which would
cause a kernel oops in vsnprintf() since it only allows passing a NULL ptr
when the length is also 0. Also, we need to filter out the negative values
of the len parameter as these will result in a really huge buffer since
snprintf() takes size_t parameter while ours is ssize_t...

Found by Linux Verification Center (linuxtesting.org) with the Svace static
analysis tool.

Signed-off-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/1d211023-3923-685b-20f0-f3f90ea56e1f@omp.ru
Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/of/module.c b/drivers/of/module.c
index 0e8aa974f0f2bb5262dfbc8b03978b6381bfd61e..f58e624953a20f25f058841b70eb9468d6f5d11e 100644 (file)
--- a/drivers/of/module.c
+++ b/drivers/of/module.c
@@ -16,6 +16,14 @@ ssize_t of_modalias(const struct device_node *np, char *str, ssize_t len)
        ssize_t csize;
        ssize_t tsize;
 
+       /*
+        * Prevent a kernel oops in vsnprintf() -- it only allows passing a
+        * NULL ptr when the length is also 0. Also filter out the negative
+        * lengths...
+        */
+       if ((len > 0 && !str) || len < 0)
+               return -EINVAL;
+
        /* Name & Type */
        /* %p eats all alphanum characters, so %c must be used here */
        csize = snprintf(str, len, "of:N%pOFn%c%s", np, 'T',