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+90b8e10515ae88228a92@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 ================================================================== --- This bug is generated by a bot. It may contain errors. See https://goo.gl/tpsmEJ for more information about syzbot. syzbot engineers can be reached at syzkaller@googlegroups.com. syzbot will keep track of this bug report. See: https://goo.gl/tpsmEJ#bug-status-tracking for how to communicate with syzbot.
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+90b8e10515ae88228a92@syzkaller.appspotmail.com Cc: <stable@vger.kernel.org> Signed-off-by: OGAWA Hirofumi <hirofumi@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 <hirofumi@mail.parknet.co.jp>