[PATCH] exfat: fix memory leak in exfat_parse_param()

[Namjae Jeon <namjae.jeon@xxxxxxxxxxx>]

From: Al Viro <viro@xxxxxxxxxxxxxxxxxx>

butt3rflyh4ck reported memory leak found by syzkaller.

A param->string held by exfat_mount_options.

BUG: memory leak

unreferenced object 0xffff88801972e090 (size 8):
  comm "syz-executor.2", pid 16298, jiffies 4295172466 (age 14.060s)
  hex dump (first 8 bytes):
    6b 6f 69 38 2d 75 00 00                          koi8-u..
  backtrace:
    [<000000005bfe35d6>] kstrdup+0x36/0x70 mm/util.c:60
    [<0000000018ed3277>] exfat_parse_param+0x160/0x5e0
fs/exfat/super.c:276
    [<000000007680462b>] vfs_parse_fs_param+0x2b4/0x610
fs/fs_context.c:147
    [<0000000097c027f2>] vfs_parse_fs_string+0xe6/0x150
fs/fs_context.c:191
    [<00000000371bf78f>] generic_parse_monolithic+0x16f/0x1f0
fs/fs_context.c:231
    [<000000005ce5eb1b>] do_new_mount fs/namespace.c:2812 [inline]
    [<000000005ce5eb1b>] do_mount+0x12bb/0x1b30 fs/namespace.c:3141
    [<00000000b642040c>] __do_sys_mount fs/namespace.c:3350 [inline]
    [<00000000b642040c>] __se_sys_mount fs/namespace.c:3327 [inline]
    [<00000000b642040c>] __x64_sys_mount+0x18f/0x230 fs/namespace.c:3327
    [<000000003b024e98>] do_syscall_64+0xf6/0x7d0
arch/x86/entry/common.c:295
    [<00000000ce2b698c>] entry_SYSCALL_64_after_hwframe+0x49/0xb3

exfat_free() should call exfat_free_iocharset() after stealing
param->string instead of kstrdup in exfat_parse_param().

Fixes: 719c1e182916 ("exfat: add super block operations")
Cc: stable@xxxxxxxxxxxxxxx # v5.7
Reported-by: butt3rflyh4ck <butterflyhuangxx@xxxxxxxxx>
Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
---
 fs/exfat/super.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/fs/exfat/super.c b/fs/exfat/super.c
index 405717e4e3ea..e650e65536f8 100644
--- a/fs/exfat/super.c
+++ b/fs/exfat/super.c
@@ -273,9 +273,8 @@ static int exfat_parse_param(struct fs_context *fc, struct fs_parameter *param)
 		break;
 	case Opt_charset:
 		exfat_free_iocharset(sbi);
-		opts->iocharset = kstrdup(param->string, GFP_KERNEL);
-		if (!opts->iocharset)
-			return -ENOMEM;
+		opts->iocharset = param->string;
+		param->string = NULL;
 		break;
 	case Opt_errors:
 		opts->errors = result.uint_32;
@@ -686,7 +685,12 @@ static int exfat_get_tree(struct fs_context *fc)
 
 static void exfat_free(struct fs_context *fc)
 {
-	kfree(fc->s_fs_info);
+	struct exfat_sb_info *sbi = fc->s_fs_info;
+
+	if (sbi) {
+		exfat_free_iocharset(sbi);
+		kfree(sbi);
+	}
 }
 
 static const struct fs_context_operations exfat_context_ops = {
-- 
2.17.1