From: David Sterba <dsterba@suse.cz>
To: fdmanana@kernel.org
Cc: linux-btrfs@vger.kernel.org
Subject: Re: [PATCH] btrfs: fix NULL pointer dereference after failure to create snapshot
Date: Mon, 7 Sep 2020 21:20:34 +0200 [thread overview]
Message-ID: <20200907192034.GC28318@twin.jikos.cz> (raw)
In-Reply-To: <20200904162257.123893-1-fdmanana@kernel.org>
On Fri, Sep 04, 2020 at 05:22:57PM +0100, fdmanana@kernel.org wrote:
> From: Filipe Manana <fdmanana@suse.com>
>
> When trying to get a new fs root for a snapshot during the transaction
> at transaction.c:create_pending_snapshot(), if btrfs_get_new_fs_root()
> fails we leave "pending->snap" pointing to an error pointer, and then
> later at ioctl.c:create_snapshot() we dereference that pointer, resulting
> in a crash:
>
> [12264.614689] BUG: kernel NULL pointer dereference, address: 00000000000007c4
> [12264.615650] #PF: supervisor write access in kernel mode
> [12264.616487] #PF: error_code(0x0002) - not-present page
> [12264.617436] PGD 0 P4D 0
> [12264.618328] Oops: 0002 [#1] PREEMPT SMP DEBUG_PAGEALLOC PTI
> [12264.619150] CPU: 0 PID: 2310635 Comm: fsstress Tainted: G W 5.9.0-rc3-btrfs-next-67 #1
> [12264.619960] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
> [12264.621769] RIP: 0010:btrfs_mksubvol+0x438/0x4a0 [btrfs]
> [12264.622528] Code: bc ef ff ff (...)
> [12264.624092] RSP: 0018:ffffaa6fc7277cd8 EFLAGS: 00010282
> [12264.624669] RAX: 00000000fffffff4 RBX: ffff9d3e8f151a60 RCX: 0000000000000000
> [12264.625249] RDX: 0000000000000001 RSI: ffffffff9d56c9be RDI: fffffffffffffff4
> [12264.625830] RBP: ffff9d3e8f151b48 R08: 0000000000000000 R09: 0000000000000000
> [12264.626413] R10: 0000000000000000 R11: 0000000000000000 R12: 00000000fffffff4
> [12264.626994] R13: ffff9d3ede380538 R14: ffff9d3ede380500 R15: ffff9d3f61b2eeb8
> [12264.627582] FS: 00007f140d5d8200(0000) GS:ffff9d3fb5e00000(0000) knlGS:0000000000000000
> [12264.628176] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [12264.628773] CR2: 00000000000007c4 CR3: 000000020f8e8004 CR4: 00000000003706f0
> [12264.629379] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [12264.629994] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> [12264.630594] Call Trace:
> [12264.631227] btrfs_mksnapshot+0x7b/0xb0 [btrfs]
> [12264.631840] __btrfs_ioctl_snap_create+0x16f/0x1a0 [btrfs]
> [12264.632458] btrfs_ioctl_snap_create_v2+0xb0/0xf0 [btrfs]
> [12264.633078] btrfs_ioctl+0x1864/0x3130 [btrfs]
> [12264.633689] ? do_sys_openat2+0x1a7/0x2d0
> [12264.634295] ? kmem_cache_free+0x147/0x3a0
> [12264.634899] ? __x64_sys_ioctl+0x83/0xb0
> [12264.635488] __x64_sys_ioctl+0x83/0xb0
> [12264.636058] do_syscall_64+0x33/0x80
> [12264.636616] entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
> (gdb) list *(btrfs_mksubvol+0x438)
> 0x7c7b8 is in btrfs_mksubvol (fs/btrfs/ioctl.c:858).
> 853 ret = 0;
> 854 pending_snapshot->anon_dev = 0;
> 855 fail:
> 856 /* Prevent double freeing of anon_dev */
> 857 if (ret && pending_snapshot->snap)
> 858 pending_snapshot->snap->anon_dev = 0;
> 859 btrfs_put_root(pending_snapshot->snap);
> 860 btrfs_subvolume_release_metadata(root, &pending_snapshot->block_rsv);
> 861 free_pending:
> 862 if (pending_snapshot->anon_dev)
>
> So fix this by setting "pending->snap" to NULL if we get an error from the
> call to btrfs_get_new_fs_root() at transaction.c:create_pending_snapshot().
>
> Fixes: 2dfb1e43f57dd3 ("btrfs: preallocate anon block device at first phase of snapshot creation")
> Signed-off-by: Filipe Manana <fdmanana@suse.com>
Added to misc-next and queued for 5.9-rc, thanks.
next prev parent reply other threads:[~2020-09-07 19:21 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-04 16:22 [PATCH] btrfs: fix NULL pointer dereference after failure to create snapshot fdmanana
2020-09-07 19:20 ` David Sterba [this message]
2020-09-07 23:56 ` Anand Jain
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