[PATCH V2] Fix NULL dereference in super_by_fd

[lixiaokeng <lixiaokeng@xxxxxxxxxx>]

When we create 100 partitions(major is 259 not 254) in a raid device,
mdadm may coredump:

Core was generated by `/usr/sbin/mdadm --detail --export /dev/md1p3'.
Program terminated with signal SIGSEGV, Segmentation fault.
#0  __strlen_sse2 ()
    at ../sysdeps/x86_64/multiarch/strlen-vec.S:126
126		movdqu	(%rax), %xmm4
(gdb) bt
#0  __strlen_sse2 ()
    at ../sysdeps/x86_64/multiarch/strlen-vec.S:126
#1  0x00007f1944659139 in __strcpy_chk (
    dest=dest@entry=0x55ea8d7c23ac "", src=0x0,
    destlen=destlen@entry=32) at strcpy_chk.c:28
#2  0x000055ea8d10b66d in strcpy (__src=<optimized out>,
    __dest=0x55ea8d7c23ac "")
    at /usr/include/bits/string_fortified.h:79
#3  super_by_fd (fd=fd@entry=3,
    subarrayp=subarrayp@entry=0x7ffe6a1dff08) at util.c:1289
#4  0x000055ea8d11b3a6 in Detail (
    dev=0x7ffe6a1e2f22 "/dev/md1p3", c=0x7ffe6a1e1700)
    at Detail.c:101
#5  0x000055ea8d101e61 in misc_list (c=<optimized out>,
    ss=<optimized out>, dump_directory=<optimized out>,
    ident=<optimized out>, devlist=<optimized out>)
    at mdadm.c:1959
#6  main (argc=<optimized out>, argv=<optimized out>)
    at mdadm.c:1629

The direct cause is fd2devnm return NULL. Here add a check.

Signed-off-by:Lixiaokeng<lixiaokeng@xxxxxxxxxx>
Signed-off-by:Wuguanghao<wuguanghao3@xxxxxxxxxx>
---
 mapfile.c | 4 ++++
 util.c    | 7 ++++++-
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/mapfile.c b/mapfile.c
index 8d7acb3..f72fe0d 100644
--- a/mapfile.c
+++ b/mapfile.c
@@ -292,6 +292,10 @@ struct map_ent *map_by_uuid(struct map_ent **map, int uuid[4])
 struct map_ent *map_by_devnm(struct map_ent **map, char *devnm)
 {
 	struct map_ent *mp;
+
+	if (!devnm)
+		return NULL;
+
 	if (!*map)
 		map_read(map);

diff --git a/util.c b/util.c
index 64dd409..3a84ee3 100644
--- a/util.c
+++ b/util.c
@@ -1241,6 +1241,11 @@ struct supertype *super_by_fd(int fd, char **subarrayp)
 	int i;
 	char *subarray = NULL;
 	char container[32] = "";
+	char *devnm = NULL;
+
+	devnm = fd2devnm(fd);
+	if (!devnm)
+		return NULL;

 	sra = sysfs_read(fd, NULL, GET_VERSION);

@@ -1286,7 +1291,7 @@ struct supertype *super_by_fd(int fd, char **subarrayp)
 		if (subarrayp)
 			*subarrayp = subarray;
 		strcpy(st->container_devnm, container);
-		strcpy(st->devnm, fd2devnm(fd));
+		strcpy(st->devnm, devnm);
 	} else
 		free(subarray);

-- 
1.8.3.1