[syzbot] [f2fs?] memory leak in f2fs_apply_options

[syzbot <syzbot+6c000dea1a93b4f5905c@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    c339f4010dea Merge tag 'platform-drivers-x86-v7.4-1' of gi..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15fbdd95580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=73ec643490576dec
dashboard link: https://syzkaller.appspot.com/bug?extid=6c000dea1a93b4f5905c
compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=13c1448d580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/533212b95d17/disk-c339f401.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/5cb62d3629c7/vmlinux-c339f401.xz
kernel image: https://storage.googleapis.com/syzbot-assets/12da5b4ca87c/bzImage-c339f401.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/546324936b23/mount_0.gz
  fsck result: failed (log: https://syzkaller.appspot.com/x/fsck.log?x=17480929580000)

AI-generated root cause summary:
In F2FS, when remounting a filesystem with an empty journalled quota option
(such as 'usrjquota='), f2fs_apply_quota_options() overwrites
F2FS_OPTION(sbi).s_qf_names[i] with NULL without freeing the previously
allocated quota filename string. While __f2fs_remount() duplicates the existing
quota file names into org_mount_opt via kstrdup() at the start of remount and
frees them upon successful completion, this only frees the temporary backup
copy, leaving the original allocated string orphaned. This results in a kernel
heap memory leak on every remount that clears a journalled quota filename
option.

full analysis:  https://syzkaller.appspot.com/x/ai_root_cause?x=6c000dea1a93b4f5905c

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+6c000dea1a93b4f5905c@syzkaller.appspotmail.com

BUG: memory leak
unreferenced object 0xffff888128b26a10 (size 8):
  comm "syz.0.17", pid 5977, jiffies 4294944034
  hex dump (first 8 bytes):
    66 32 66 73 00 00 00 00                          f2fs....
  backtrace (crc 49a76b1f):
    kmemleak_alloc_recursive include/linux/kmemleak.h:44 [inline]
    slab_post_alloc_hook mm/slub.c:4733 [inline]
    slab_alloc_node mm/slub.c:5033 [inline]
    __do_kmalloc_node mm/slub.c:5530 [inline]
    __kmalloc_node_track_caller_noprof+0x3e0/0x530 mm/slub.c:5662
    __kmemdup_nul mm/util.c:64 [inline]
    kstrdup+0x3c/0x80 mm/util.c:84
    f2fs_apply_quota_options fs/f2fs/super.c:1661 [inline]
    f2fs_apply_options+0x99c/0xb70 fs/f2fs/super.c:1804
    f2fs_fill_super+0xfc4/0x43f0 fs/f2fs/super.c:5288
    get_tree_bdev_flags+0x1c0/0x290 fs/super.c:1883
    vfs_get_tree+0x30/0x120 fs/super.c:1943
    fc_mount fs/namespace.c:1282 [inline]
    do_new_mount_fc fs/namespace.c:3910 [inline]
    do_new_mount fs/namespace.c:3986 [inline]
    path_mount+0x5a9/0x1580 fs/namespace.c:4337
    do_mount fs/namespace.c:4350 [inline]
    __do_sys_mount fs/namespace.c:4565 [inline]
    __se_sys_mount fs/namespace.c:4542 [inline]
    __x64_sys_mount+0x1a3/0x1e0 fs/namespace.c:4542
    do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
    do_syscall_64+0xe9/0x530 arch/x86/entry/syscall_64.c:84
    entry_SYSCALL_64_after_hwframe+0x77/0x7f

connection error: failed to recv *flatrpc.ExecutorMessageRawT: EOF


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