KASAN: invalid-free in fat_fill_super

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 98be45067040 Add linux-next specific files for 20180711
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=120b1ed0400000
kernel config: https://syzkaller.appspot.com/x/.config?x=3f3b3673fec35d01
dashboard link: https://syzkaller.appspot.com/bug?extid=90b8e10515ae88228a92
compiler: gcc (GCC) 8.0.1 20180413 (experimental)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+90b8e1...@syzkaller.appspotmail.com

RDX: 00007fd0b961ead0 RSI: 0000000020000080 RDI: 00007fd0b961eaf0
RBP: 0000000020000080 R08: 00007fd0b961eb30 R09: 00007fd0b961ead0
R10: 0000000000000000 R11: 0000000000000206 R12: 0000000000000015
R13: 0000000000000000 R14: 00000000004d3fd0 R15: 000000000000004a
==================================================================
BUG: KASAN: double-free or invalid-free in fat_fill_super+0xc84/0x4400
fs/fat/inode.c:1882

CPU: 1 PID: 31888 Comm: syz-executor6 Not tainted 4.18.0-rc4-next-20180711+
#4
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x1c9/0x2b4 lib/dump_stack.c:113
print_address_description+0x6c/0x20b mm/kasan/report.c:256
kasan_report_invalid_free+0x64/0xa0 mm/kasan/report.c:336
__kasan_slab_free+0x150/0x170 mm/kasan/kasan.c:501
kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528
__cache_free mm/slab.c:3498 [inline]
kfree+0xd9/0x260 mm/slab.c:3813
fat_fill_super+0xc84/0x4400 fs/fat/inode.c:1882
vfat_fill_super+0x31/0x40 fs/fat/namei_vfat.c:1049
mount_bdev+0x314/0x3e0 fs/super.c:1344
vfat_mount+0x3c/0x50 fs/fat/namei_vfat.c:1056
legacy_get_tree+0x118/0x440 fs/fs_context.c:659
vfs_get_tree+0x1cb/0x5c0 fs/super.c:1743
do_new_mount fs/namespace.c:2567 [inline]
do_mount+0x6c1/0x1fb0 fs/namespace.c:2889
ksys_mount+0x12d/0x140 fs/namespace.c:3105
__do_sys_mount fs/namespace.c:3119 [inline]
__se_sys_mount fs/namespace.c:3116 [inline]
__x64_sys_mount+0xbe/0x150 fs/namespace.c:3116
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45885a
Code: b8 a6 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 dd 8f fb ff c3 66 2e 0f
1f 84 00 00 00 00 00 66 90 49 89 ca b8 a5 00 00 00 0f 05 <48> 3d 01 f0 ff
ff 0f 83 ba 8f fb ff c3 66 0f 1f 84 00 00 00 00 00
RSP: 002b:00007fd0b961ea88 EFLAGS: 00000206 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007fd0b961eb30 RCX: 000000000045885a
RDX: 00007fd0b961ead0 RSI: 0000000020000080 RDI: 00007fd0b961eaf0
RBP: 0000000020000080 R08: 00007fd0b961eb30 R09: 00007fd0b961ead0
R10: 0000000000000000 R11: 0000000000000206 R12: 0000000000000015
R13: 0000000000000000 R14: 00000000004d3fd0 R15: 000000000000004a

Allocated by task 31888:
save_stack+0x43/0xd0 mm/kasan/kasan.c:448
set_track mm/kasan/kasan.c:460 [inline]
kasan_kmalloc+0xc4/0xe0 mm/kasan/kasan.c:553
__do_kmalloc mm/slab.c:3718 [inline]
__kmalloc+0x14e/0x760 mm/slab.c:3727
kmalloc include/linux/slab.h:518 [inline]
match_strdup+0x5e/0xa0 lib/parser.c:331
parse_options+0xc7d/0x1a10 fs/fat/inode.c:1291
fat_fill_super+0x2b3/0x4400 fs/fat/inode.c:1631
vfat_fill_super+0x31/0x40 fs/fat/namei_vfat.c:1049
mount_bdev+0x314/0x3e0 fs/super.c:1344
vfat_mount+0x3c/0x50 fs/fat/namei_vfat.c:1056
legacy_get_tree+0x118/0x440 fs/fs_context.c:659
vfs_get_tree+0x1cb/0x5c0 fs/super.c:1743
do_new_mount fs/namespace.c:2567 [inline]
do_mount+0x6c1/0x1fb0 fs/namespace.c:2889
ksys_mount+0x12d/0x140 fs/namespace.c:3105
__do_sys_mount fs/namespace.c:3119 [inline]
__se_sys_mount fs/namespace.c:3116 [inline]
__x64_sys_mount+0xbe/0x150 fs/namespace.c:3116
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 31888:
save_stack+0x43/0xd0 mm/kasan/kasan.c:448
set_track mm/kasan/kasan.c:460 [inline]
__kasan_slab_free+0x11a/0x170 mm/kasan/kasan.c:521
kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528
__cache_free mm/slab.c:3498 [inline]
kfree+0xd9/0x260 mm/slab.c:3813
parse_options+0xc70/0x1a10 fs/fat/inode.c:1290
fat_fill_super+0x2b3/0x4400 fs/fat/inode.c:1631
vfat_fill_super+0x31/0x40 fs/fat/namei_vfat.c:1049
mount_bdev+0x314/0x3e0 fs/super.c:1344
vfat_mount+0x3c/0x50 fs/fat/namei_vfat.c:1056
legacy_get_tree+0x118/0x440 fs/fs_context.c:659
vfs_get_tree+0x1cb/0x5c0 fs/super.c:1743
do_new_mount fs/namespace.c:2567 [inline]
do_mount+0x6c1/0x1fb0 fs/namespace.c:2889
ksys_mount+0x12d/0x140 fs/namespace.c:3105
__do_sys_mount fs/namespace.c:3119 [inline]
__se_sys_mount fs/namespace.c:3116 [inline]
__x64_sys_mount+0xbe/0x150 fs/namespace.c:3116
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff880190d60c80
which belongs to the cache kmalloc-32 of size 32
The buggy address is located 0 bytes inside of
32-byte region [ffff880190d60c80, ffff880190d60ca0)
The buggy address belongs to the page:
page:ffffea0006435800 count:1 mapcount:0 mapping:ffff8801da8001c0
index:0xffff880190d60fc1
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffffea00073fe648 ffffea00060af588 ffff8801da8001c0
raw: ffff880190d60fc1 ffff880190d60000 000000010000000d 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff880190d60b80: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
ffff880190d60c00: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
> ffff880190d60c80: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
^
ffff880190d60d00: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
ffff880190d60d80: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
==================================================================


---
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[OGAWA Hirofumi]

In parse_options(), if match_strdup() failed, parse_options() leaves
opts->iocharset in unexpected state (i.e. still pointing the freed
string). And this can be the cause of double free.

To fix, this initialize opts->iocharset always when freeing.

Reported-by: syzbot+90b8e1...@syzkaller.appspotmail.com
Cc: <sta...@vger.kernel.org>
Signed-off-by: OGAWA Hirofumi <hiro...@mail.parknet.co.jp>
---

fs/fat/inode.c | 20 +++++++++++++-------
1 file changed, 13 insertions(+), 7 deletions(-)

diff -puN fs/fat/inode.c~fat-fix-kmalloc-failure fs/fat/inode.c
--- linux/fs/fat/inode.c~fat-fix-kmalloc-failure 2018-07-12 12:20:30.388600735 +0900
+++ linux-hirofumi/fs/fat/inode.c 2018-07-12 15:09:48.764070539 +0900
@@ -703,13 +703,21 @@ static void fat_set_state(struct super_b
brelse(bh);
}

+static void fat_reset_iocharset(struct fat_mount_options *opts)
+{
+ if (opts->iocharset != fat_default_iocharset) {
+ /* Note: opts->iocharset can be NULL here */
+ kfree(opts->iocharset);
+ opts->iocharset = fat_default_iocharset;
+ }
+}
+
static void delayed_free(struct rcu_head *p)
{
struct msdos_sb_info *sbi = container_of(p, struct msdos_sb_info, rcu);
unload_nls(sbi->nls_disk);
unload_nls(sbi->nls_io);
- if (sbi->options.iocharset != fat_default_iocharset)
- kfree(sbi->options.iocharset);
+ fat_reset_iocharset(&sbi->options);
kfree(sbi);
}

@@ -1124,7 +1132,7 @@ static int parse_options(struct super_bl
opts->fs_fmask = opts->fs_dmask = current_umask();
opts->allow_utime = -1;
opts->codepage = fat_default_codepage;
- opts->iocharset = fat_default_iocharset;
+ fat_reset_iocharset(opts);
if (is_vfat) {
opts->shortname = VFAT_SFN_DISPLAY_WINNT|VFAT_SFN_CREATE_WIN95;
opts->rodir = 0;
@@ -1281,8 +1289,7 @@ static int parse_options(struct super_bl

/* vfat specific */
case Opt_charset:
- if (opts->iocharset != fat_default_iocharset)
- kfree(opts->iocharset);
+ fat_reset_iocharset(opts);
iocharset = match_strdup(&args[0]);
if (!iocharset)
return -ENOMEM;
@@ -1873,8 +1880,7 @@ out_fail:
iput(fat_inode);
unload_nls(sbi->nls_io);
unload_nls(sbi->nls_disk);
- if (sbi->options.iocharset != fat_default_iocharset)
- kfree(sbi->options.iocharset);
+ fat_reset_iocharset(&sbi->options);
sb->s_fs_info = NULL;
kfree(sbi);
return error;
_

--
OGAWA Hirofumi <hiro...@mail.parknet.co.jp>