[PATCH 4.4 17/41] sparc: avoid stringop-overread errors

Greg Kroah-Hartman
2021-10-04T12:54:29Z

From: Linus Torvalds <torvalds@linux-foundation.org>

[ Upstream commit fc7c028dcdbfe981bca75d2a7b95f363eb691ef3 ]

The sparc mdesc code does pointer games with 'struct mdesc_hdr', but
didn't describe to the compiler how that header is then followed by the
data that the header describes.

As a result, gcc is now unhappy since it does stricter pointer range
tracking, and doesn't understand about how these things work. This
results in various errors like:

arch/sparc/kernel/mdesc.c: In function ‘mdesc_node_by_name’:
arch/sparc/kernel/mdesc.c:647:22: error: ‘strcmp’ reading 1 or more bytes from a region of size 0 [-Werror=stringop-overread]
647 | if (!strcmp(names + ep[ret].name_offset, name))
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

which are easily avoided by just describing 'struct mdesc_hdr' better,
and making the node_block() helper function look into that unsized
data[] that follows the header.

This makes the sparc64 build happy again at least for my cross-compiler
version (gcc version 11.2.1).

Link: https://lore.kernel.org/lkml/CAHk-=wi4NW3NC0xWykkw=6LnjQD6D_rtRtxY9g8gQAJXtQMi8A@mail.gmail.com/
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/sparc/kernel/mdesc.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/sparc/kernel/mdesc.c b/arch/sparc/kernel/mdesc.c
index 6f80936e0eea..75445ba7e237 100644
--- a/arch/sparc/kernel/mdesc.c
+++ b/arch/sparc/kernel/mdesc.c
@@ -37,6 +37,7 @@ struct mdesc_hdr {
u32 node_sz; /* node block size */
u32 name_sz; /* name block size */
u32 data_sz; /* data block size */
+ char data[];
} __attribute__((aligned(16)));

struct mdesc_elem {
@@ -369,7 +370,7 @@ out:

static struct mdesc_elem *node_block(struct mdesc_hdr *mdesc)
{
- return (struct mdesc_elem *) (mdesc + 1);
+ return (struct mdesc_elem *) mdesc->data;
}

static void *name_block(struct mdesc_hdr *mdesc)
--
2.33.0