[PATCH] perf buildid: fix off-by-one in write_buildid()

[Andrey Ryabinin <aryabinin@virtuozzo.com>]

write_buildid() increments 'name_len' with intention to take into account
trailing zero byte. However, 'name_len' was already incremented in
machine__write_buildid_table() before.
So this leads to out-of-bounds read in do_write():

$ ./perf record sleep 0
[ perf record: Woken up 1 times to write data ]
=================================================================
==15899==ERROR: AddressSanitizer: global-buffer-overflow on address 0x00000099fc92 at pc 0x7f1aa9c7eab5 bp 0x7fff940f84d0 sp 0x7fff940f7c78
READ of size 19 at 0x00000099fc92 thread T0
    #0 0x7f1aa9c7eab4  (/usr/lib/gcc/x86_64-pc-linux-gnu/5.3.0/libasan.so.2+0x44ab4)
    #1 0x649c5b in do_write util/header.c:67
    #2 0x649c5b in write_padded util/header.c:82
    #3 0x57e8bc in write_buildid util/build-id.c:239
    #4 0x57e8bc in machine__write_buildid_table util/build-id.c:278
...

0x00000099fc92 is located 0 bytes to the right of global variable '*.LC99' defined in 'util/symbol.c' (0x99fc80) of size 18
  '*.LC99' is ascii string '[kernel.kallsyms]'
...

Shadow bytes around the buggy address:
  0x00008012bf80: f9 f9 f9 f9 00 00 00 00 00 00 03 f9 f9 f9 f9 f9
=>0x00008012bf90: 00 00[02]f9 f9 f9 f9 f9 00 00 00 00 00 05 f9 f9
  0x00008012bfa0: f9 f9 f9 f9 00 03 f9 f9 f9 f9 f9 f9 00 00 00 00

Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
---
 tools/perf/util/build-id.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/perf/util/build-id.c b/tools/perf/util/build-id.c
index 0573c2e..a1ff68b 100644
--- a/tools/perf/util/build-id.c
+++ b/tools/perf/util/build-id.c
@@ -235,7 +235,7 @@ static int write_buildid(const char *name, size_t name_len, u8 *build_id,
 	if (err < 0)
 		return err;
 
-	return write_padded(fd, name, name_len + 1, len);
+	return write_padded(fd, name, name_len, len);
 }
 
 static int machine__write_buildid_table(struct machine *machine, int fd)
-- 
2.7.3