[PATCH 6.18 003/686] cxl/features: Ensure that count is set before access to ent[] __counted_by()

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

6.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Ashok Raj <ashok.raj@oss.qualcomm.com>

commit c1031c2474f73261d8d5e4deef2b5dc20fb964f5 upstream.

get_supported_features() assigns entries->num_features only after the
memcpy() loop that fills entries->ent[] has already run. Since ent[]
is __counted_by(num_features), the compiler's bounds instrumentation
sees a 0-length array during that loop and FORTIFY_SOURCE trips on
the memcpy. Set @num_features right after allocation, before any
write into ent[], so the bound is correct for the whole lifetime of
the array.

This was found via a fortify panic:

 memcpy: detected buffer overflow: 384 byte write of buffer size 0
 WARNING: lib/string_helpers.c:1035 at __fortify_report+0x54/0xa0
 kernel BUG at lib/string_helpers.c:1043!
 Call trace:
  __fortify_panic+0x10/0x18
  get_supported_features.isra.0+0x4a0/0x4d0 [cxl_core]
  devm_cxl_setup_features+0x84/0x120 [cxl_core]
  cxl_pci_probe+0x254/0x5e0 [cxl_pci]

Same class of bug, same fix shape as commit 6c9d2e87df40
("cxl/fwctl: Fix __fortify_panic"), which fixed the analogous issue
in cxlctl_get_supported_features() but missed this one.

[ dj: Fixed up title typo per Jonathan. ]

Fixes: f0e6a2329bf9 ("cxl: Add Get Supported Features command for kernel usage")
Signed-off-by: Ashok Raj <ashok.raj@oss.qualcomm.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@oss.qualcomm.com>
Link: https://patch.msgid.link/20260911215304.1816467-1-ashok.raj@oss.qualcomm.com
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Ahmed Abdelfattah <me@ahmedabdelfattah.dev>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/cxl/core/features.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/cxl/core/features.c b/drivers/cxl/core/features.c
index bb73f205f16cf..0ea5a31275d38 100644
--- a/drivers/cxl/core/features.c
+++ b/drivers/cxl/core/features.c
@@ -97,6 +97,7 @@ get_supported_features(struct cxl_features_state *cxlfs)
 		kvmalloc(struct_size(entries, ent, count), GFP_KERNEL);
 	if (!entries)
 		return NULL;
+	entries->num_features = count;
 
 	struct cxl_mbox_get_sup_feats_out *mbox_out __free(kvfree) =
 		kvmalloc(cxl_mbox->payload_size, GFP_KERNEL);
@@ -174,7 +175,6 @@ get_supported_features(struct cxl_features_state *cxlfs)
 		start += num_entries;
 	} while (remain_feats);
 
-	entries->num_features = count;
 	entries->num_user_features = user_feats;
 
 	return no_free_ptr(entries);
-- 
2.53.0