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    Subject[PATCH 4.14 18/64] btrfs: fix double free on ulist after backref resolution failure
    Date
    From: Filipe Manana <fdmanana@suse.com>

    commit 580c079b5766ac706f56eec5c79aee4bf929fef6 upstream.

    At btrfs_find_all_roots_safe() we allocate a ulist and set the **roots
    argument to point to it. However if later we fail due to an error returned
    by find_parent_nodes(), we free that ulist but leave a dangling pointer in
    the **roots argument. Upon receiving the error, a caller of this function
    can attempt to free the same ulist again, resulting in an invalid memory
    access.

    One such scenario is during qgroup accounting:

    btrfs_qgroup_account_extents()

    --> calls btrfs_find_all_roots() passes &new_roots (a stack allocated
    pointer) to btrfs_find_all_roots()

    --> btrfs_find_all_roots() just calls btrfs_find_all_roots_safe()
    passing &new_roots to it

    --> allocates ulist and assigns its address to **roots (which
    points to new_roots from btrfs_qgroup_account_extents())

    --> find_parent_nodes() returns an error, so we free the ulist
    and leave **roots pointing to it after returning

    --> btrfs_qgroup_account_extents() sees btrfs_find_all_roots() returned
    an error and jumps to the label 'cleanup', which just tries to
    free again the same ulist

    Stack trace example:

    ------------[ cut here ]------------
    BTRFS: tree first key check failed
    WARNING: CPU: 1 PID: 1763215 at fs/btrfs/disk-io.c:422 btrfs_verify_level_key+0xe0/0x180 [btrfs]
    Modules linked in: dm_snapshot dm_thin_pool (...)
    CPU: 1 PID: 1763215 Comm: fsstress Tainted: G W 5.8.0-rc3-btrfs-next-64 #1
    Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
    RIP: 0010:btrfs_verify_level_key+0xe0/0x180 [btrfs]
    Code: 28 5b 5d (...)
    RSP: 0018:ffffb89b473779a0 EFLAGS: 00010286
    RAX: 0000000000000000 RBX: ffff90397759bf08 RCX: 0000000000000000
    RDX: 0000000000000001 RSI: 0000000000000027 RDI: 00000000ffffffff
    RBP: ffff9039a419c000 R08: 0000000000000000 R09: 0000000000000000
    R10: 0000000000000000 R11: ffffb89b43301000 R12: 000000000000005e
    R13: ffffb89b47377a2e R14: ffffb89b473779af R15: 0000000000000000
    FS: 00007fc47e1e1000(0000) GS:ffff9039ac200000(0000) knlGS:0000000000000000
    CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    CR2: 00007fc47e1df000 CR3: 00000003d9e4e001 CR4: 00000000003606e0
    DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
    DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
    Call Trace:
    read_block_for_search+0xf6/0x350 [btrfs]
    btrfs_next_old_leaf+0x242/0x650 [btrfs]
    resolve_indirect_refs+0x7cf/0x9e0 [btrfs]
    find_parent_nodes+0x4ea/0x12c0 [btrfs]
    btrfs_find_all_roots_safe+0xbf/0x130 [btrfs]
    btrfs_qgroup_account_extents+0x9d/0x390 [btrfs]
    btrfs_commit_transaction+0x4f7/0xb20 [btrfs]
    btrfs_sync_file+0x3d4/0x4d0 [btrfs]
    do_fsync+0x38/0x70
    __x64_sys_fdatasync+0x13/0x20
    do_syscall_64+0x5c/0xe0
    entry_SYSCALL_64_after_hwframe+0x44/0xa9
    RIP: 0033:0x7fc47e2d72e3
    Code: Bad RIP value.
    RSP: 002b:00007fffa32098c8 EFLAGS: 00000246 ORIG_RAX: 000000000000004b
    RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007fc47e2d72e3
    RDX: 00007fffa3209830 RSI: 00007fffa3209830 RDI: 0000000000000003
    RBP: 000000000000072e R08: 0000000000000001 R09: 0000000000000003
    R10: 0000000000000000 R11: 0000000000000246 R12: 00000000000003e8
    R13: 0000000051eb851f R14: 00007fffa3209970 R15: 00005607c4ac8b50
    irq event stamp: 0
    hardirqs last enabled at (0): [<0000000000000000>] 0x0
    hardirqs last disabled at (0): [<ffffffffb8eb5e85>] copy_process+0x755/0x1eb0
    softirqs last enabled at (0): [<ffffffffb8eb5e85>] copy_process+0x755/0x1eb0
    softirqs last disabled at (0): [<0000000000000000>] 0x0
    ---[ end trace 8639237550317b48 ]---
    BTRFS error (device sdc): tree first key mismatch detected, bytenr=62324736 parent_transid=94 key expected=(262,108,1351680) has=(259,108,1921024)
    general protection fault, probably for non-canonical address 0x6b6b6b6b6b6b6b6b: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC PTI
    CPU: 2 PID: 1763215 Comm: fsstress Tainted: G W 5.8.0-rc3-btrfs-next-64 #1
    Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
    RIP: 0010:ulist_release+0x14/0x60 [btrfs]
    Code: c7 07 00 (...)
    RSP: 0018:ffffb89b47377d60 EFLAGS: 00010282
    RAX: 6b6b6b6b6b6b6b6b RBX: ffff903959b56b90 RCX: 0000000000000000
    RDX: 0000000000000001 RSI: 0000000000270024 RDI: ffff9036e2adc840
    RBP: ffff9036e2adc848 R08: 0000000000000000 R09: 0000000000000000
    R10: 0000000000000000 R11: 0000000000000000 R12: ffff9036e2adc840
    R13: 0000000000000015 R14: ffff9039a419ccf8 R15: ffff90395d605840
    FS: 00007fc47e1e1000(0000) GS:ffff9039ac600000(0000) knlGS:0000000000000000
    CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    CR2: 00007f8c1c0a51c8 CR3: 00000003d9e4e004 CR4: 00000000003606e0
    DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
    DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
    Call Trace:
    ulist_free+0x13/0x20 [btrfs]
    btrfs_qgroup_account_extents+0xf3/0x390 [btrfs]
    btrfs_commit_transaction+0x4f7/0xb20 [btrfs]
    btrfs_sync_file+0x3d4/0x4d0 [btrfs]
    do_fsync+0x38/0x70
    __x64_sys_fdatasync+0x13/0x20
    do_syscall_64+0x5c/0xe0
    entry_SYSCALL_64_after_hwframe+0x44/0xa9
    RIP: 0033:0x7fc47e2d72e3
    Code: Bad RIP value.
    RSP: 002b:00007fffa32098c8 EFLAGS: 00000246 ORIG_RAX: 000000000000004b
    RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007fc47e2d72e3
    RDX: 00007fffa3209830 RSI: 00007fffa3209830 RDI: 0000000000000003
    RBP: 000000000000072e R08: 0000000000000001 R09: 0000000000000003
    R10: 0000000000000000 R11: 0000000000000246 R12: 00000000000003e8
    R13: 0000000051eb851f R14: 00007fffa3209970 R15: 00005607c4ac8b50
    Modules linked in: dm_snapshot dm_thin_pool (...)
    ---[ end trace 8639237550317b49 ]---
    RIP: 0010:ulist_release+0x14/0x60 [btrfs]
    Code: c7 07 00 (...)
    RSP: 0018:ffffb89b47377d60 EFLAGS: 00010282
    RAX: 6b6b6b6b6b6b6b6b RBX: ffff903959b56b90 RCX: 0000000000000000
    RDX: 0000000000000001 RSI: 0000000000270024 RDI: ffff9036e2adc840
    RBP: ffff9036e2adc848 R08: 0000000000000000 R09: 0000000000000000
    R10: 0000000000000000 R11: 0000000000000000 R12: ffff9036e2adc840
    R13: 0000000000000015 R14: ffff9039a419ccf8 R15: ffff90395d605840
    FS: 00007fc47e1e1000(0000) GS:ffff9039ad200000(0000) knlGS:0000000000000000
    CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    CR2: 00007f6a776f7d40 CR3: 00000003d9e4e002 CR4: 00000000003606e0
    DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
    DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400

    Fix this by making btrfs_find_all_roots_safe() set *roots to NULL after
    it frees the ulist.

    Fixes: 8da6d5815c592b ("Btrfs: added btrfs_find_all_roots()")
    CC: stable@vger.kernel.org # 4.4+
    Reviewed-by: Josef Bacik <josef@toxicpanda.com>
    Signed-off-by: Filipe Manana <fdmanana@suse.com>
    Reviewed-by: David Sterba <dsterba@suse.com>
    Signed-off-by: David Sterba <dsterba@suse.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    fs/btrfs/backref.c | 1 +
    1 file changed, 1 insertion(+)

    --- a/fs/btrfs/backref.c
    +++ b/fs/btrfs/backref.c
    @@ -1420,6 +1420,7 @@ static int btrfs_find_all_roots_safe(str
    if (ret < 0 && ret != -ENOENT) {
    ulist_free(tmp);
    ulist_free(*roots);
    + *roots = NULL;
    return ret;
    }
    node = ulist_next(tmp, &uiter);

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