[PATCH] Bluetooth: L2CAP: Elide a string overflow warning

[Palmer Dabbelt <palmer@rivosinc.com>]

From: Palmer Dabbelt <palmer@rivosinc.com>

Without this I get a string op warning related to copying from a
possibly NULL pointer.  I think the warning is spurious, but it's
tripping up allmodconfig.

In file included from /scratch/merges/ko-linux-next/linux/include/linux/string.h:253,
                 from /scratch/merges/ko-linux-next/linux/include/linux/bitmap.h:11,
                 from /scratch/merges/ko-linux-next/linux/include/linux/cpumask.h:12,
                 from /scratch/merges/ko-linux-next/linux/include/linux/mm_types_task.h:14,
                 from /scratch/merges/ko-linux-next/linux/include/linux/mm_types.h:5,
                 from /scratch/merges/ko-linux-next/linux/include/linux/buildid.h:5,
                 from /scratch/merges/ko-linux-next/linux/include/linux/module.h:14,
                 from /scratch/merges/ko-linux-next/linux/net/bluetooth/l2cap_core.c:31:
In function 'memcmp',
    inlined from 'bacmp' at /scratch/merges/ko-linux-next/linux/include/net/bluetooth/bluetooth.h:347:9,
    inlined from 'l2cap_global_chan_by_psm' at /scratch/merges/ko-linux-next/linux/net/bluetooth/l2cap_core.c:2003:15:
/scratch/merges/ko-linux-next/linux/include/linux/fortify-string.h:44:33: error: '__builtin_memcmp' specified bound 6 exceeds source size 0 [-Werror=stringop-overread]
   44 | #define __underlying_memcmp     __builtin_memcmp
      |                                 ^
/scratch/merges/ko-linux-next/linux/include/linux/fortify-string.h:420:16: note: in expansion of macro '__underlying_memcmp'
  420 |         return __underlying_memcmp(p, q, size);
      |                ^~~~~~~~~~~~~~~~~~~
In function 'memcmp',
    inlined from 'bacmp' at /scratch/merges/ko-linux-next/linux/include/net/bluetooth/bluetooth.h:347:9,
    inlined from 'l2cap_global_chan_by_psm' at /scratch/merges/ko-linux-next/linux/net/bluetooth/l2cap_core.c:2004:15:
/scratch/merges/ko-linux-next/linux/include/linux/fortify-string.h:44:33: error: '__builtin_memcmp' specified bound 6 exceeds source size 0 [-Werror=stringop-overread]
   44 | #define __underlying_memcmp     __builtin_memcmp
      |                                 ^
/scratch/merges/ko-linux-next/linux/include/linux/fortify-string.h:420:16: note: in expansion of macro '__underlying_memcmp'
  420 |         return __underlying_memcmp(p, q, size);
      |                ^~~~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors

Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
---
 net/bluetooth/l2cap_core.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
index cbe0cae73434..be7f47e52119 100644
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c
@@ -2000,11 +2000,13 @@ static struct l2cap_chan *l2cap_global_chan_by_psm(int state, __le16 psm,
 			}
 
 			/* Closest match */
-			src_any = !bacmp(&c->src, BDADDR_ANY);
-			dst_any = !bacmp(&c->dst, BDADDR_ANY);
-			if ((src_match && dst_any) || (src_any && dst_match) ||
-			    (src_any && dst_any))
-				c1 = c;
+			if (c) {
+				src_any = !bacmp(&c->src, BDADDR_ANY);
+				dst_any = !bacmp(&c->dst, BDADDR_ANY);
+				if ((src_match && dst_any) || (src_any && dst_match) ||
+				    (src_any && dst_any))
+					c1 = c;
+			}
 		}
 	}
 
-- 
2.34.1