[PATCH 1/2] btrfs: Fix wild memory access in compression level parser

[Qu Wenruo <wqu@suse.com>]

[BUG]
Kernel panic when mounting with "-o compress" mount option.
KASAN will report like:
------
==================================================================
BUG: KASAN: wild-memory-access in strncmp+0x31/0xc0
Read of size 1 at addr d86735fce994f800 by task mount/662
...
Call Trace:
 dump_stack+0xe3/0x175
 kasan_report+0x163/0x370
 __asan_load1+0x47/0x50
 strncmp+0x31/0xc0
 btrfs_compress_str2level+0x20/0x70 [btrfs]
 btrfs_parse_options+0xff4/0x1870 [btrfs]
 open_ctree+0x2679/0x49f0 [btrfs]
 btrfs_mount+0x1b7f/0x1d30 [btrfs]
 mount_fs+0x49/0x190
 vfs_kern_mount.part.29+0xba/0x280
 vfs_kern_mount+0x13/0x20
 btrfs_mount+0x31e/0x1d30 [btrfs]
 mount_fs+0x49/0x190
 vfs_kern_mount.part.29+0xba/0x280
 do_mount+0xaad/0x1a00
 SyS_mount+0x98/0xe0
 entry_SYSCALL_64_fastpath+0x1f/0xbe
------

[Cause]
For 'compress' and 'compress_force' options, its token doesn't expect
any parameter so its args[0] contains uninitialized data.
Accessing args[0] will cause above wild memory access.

[Fix]
For Opt_compress and Opt_compress_force, set compression level to
Z_DEFAULT_COMPRESSION manually.

NOTE: Don't set zlib compression level to 0 by default, which means no
compression.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/super.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 65af029559b5..14258671da84 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -42,6 +42,7 @@
 #include <linux/cleancache.h>
 #include <linux/ratelimit.h>
 #include <linux/btrfs.h>
+#include <linux/zlib.h>
 #include "delayed-inode.h"
 #include "ctree.h"
 #include "disk-io.h"
@@ -507,8 +508,19 @@ int btrfs_parse_options(struct btrfs_fs_info *info, char *options,
 			    token == Opt_compress_force ||
 			    strncmp(args[0].from, "zlib", 4) == 0) {
 				compress_type = "zlib";
+
 				info->compress_type = BTRFS_COMPRESS_ZLIB;
-				info->compress_level =
+				/*
+				 * args[0] contains uninitialized data since
+				 * for these tokens we don't expect any
+				 * parameter.
+				 */
+				if (token == Opt_compress ||
+				    token == Opt_compress_force)
+					info->compress_level =
+						Z_DEFAULT_COMPRESSION;
+				else
+					info->compress_level =
 					btrfs_compress_str2level(args[0].from);
 				btrfs_set_opt(info->mount_opt, COMPRESS);
 				btrfs_clear_opt(info->mount_opt, NODATACOW);
-- 
2.14.3