[PATCH 6.1.y] mm/slub: avoid accessing metadata when pointer is invalid in object_err()

[Sasha Levin <sashal@kernel.org>]

From: Li Qiong <liqiong@nfschina.com>

[ Upstream commit b4efccec8d06ceb10a7d34d7b1c449c569d53770 ]

object_err() reports details of an object for further debugging, such as
the freelist pointer, redzone, etc. However, if the pointer is invalid,
attempting to access object metadata can lead to a crash since it does
not point to a valid object.

One known path to the crash is when alloc_consistency_checks()
determines the pointer to the allocated object is invalid because of a
freelist corruption, and calls object_err() to report it. The debug code
should report and handle the corruption gracefully and not crash in the
process.

In case the pointer is NULL or check_valid_pointer() returns false for
the pointer, only print the pointer value and skip accessing metadata.

Fixes: 81819f0fc828 ("SLUB core")
Cc: <stable@vger.kernel.org>
Signed-off-by: Li Qiong <liqiong@nfschina.com>
Reviewed-by: Harry Yoo <harry.yoo@oracle.com>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
[ Adjust context ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 mm/slub.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/mm/slub.c b/mm/slub.c
index 157527d7101be..f118fcc6af6e4 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -927,7 +927,12 @@ static void object_err(struct kmem_cache *s, struct slab *slab,
 		return;
 
 	slab_bug(s, "%s", reason);
-	print_trailer(s, slab, object);
+	if (!object || !check_valid_pointer(s, slab, object)) {
+		print_slab_info(slab);
+		pr_err("Invalid pointer 0x%p\n", object);
+	} else {
+		print_trailer(s, slab, object);
+	}
 	add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
 }
 
-- 
2.51.0