From: Josef Bacik josef@toxicpanda.com
commit 0465337c5599bbe360cdcff452992a1a6b7ed2d4 upstream.
Eric reported an issue where mounting -o recovery with a fuzzed fs resulted in a kernel panic. This is because we tried to free the tree node, except it was an error from the read. Fix this by properly resetting the tree_root->node == NULL in this case. The panic was the following
BTRFS warning (device loop0): failed to read tree root BUG: kernel NULL pointer dereference, address: 000000000000001f RIP: 0010:free_extent_buffer+0xe/0x90 [btrfs] Call Trace: free_root_extent_buffers.part.0+0x11/0x30 [btrfs] free_root_pointers+0x1a/0xa2 [btrfs] open_ctree+0x1776/0x18a5 [btrfs] btrfs_mount_root.cold+0x13/0xfa [btrfs] ? selinux_fs_context_parse_param+0x37/0x80 legacy_get_tree+0x27/0x40 vfs_get_tree+0x25/0xb0 fc_mount+0xe/0x30 vfs_kern_mount.part.0+0x71/0x90 btrfs_mount+0x147/0x3e0 [btrfs] ? cred_has_capability+0x7c/0x120 ? legacy_get_tree+0x27/0x40 legacy_get_tree+0x27/0x40 vfs_get_tree+0x25/0xb0 do_mount+0x735/0xa40 __x64_sys_mount+0x8e/0xd0 do_syscall_64+0x4d/0x90 entry_SYSCALL_64_after_hwframe+0x44/0xa9
Nik says: this is problematic only if we fail on the last iteration of the loop as this results in init_tree_roots returning err value with tree_root->node = -ERR. Subsequently the caller does: fail_tree_roots which calls free_root_pointers on the bogus value.
Reported-by: Eric Sandeen sandeen@redhat.com Fixes: b8522a1e5f42 ("btrfs: Factor out tree roots initialization during mount") CC: stable@vger.kernel.org # 5.5+ Reviewed-by: Nikolay Borisov nborisov@suse.com Signed-off-by: Josef Bacik josef@toxicpanda.com Reviewed-by: David Sterba dsterba@suse.com [ add details how the pointer gets dereferenced ] Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/btrfs/disk-io.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)
--- a/fs/btrfs/disk-io.c +++ b/fs/btrfs/disk-io.c @@ -2583,10 +2583,12 @@ static int __cold init_tree_roots(struct !extent_buffer_uptodate(tree_root->node)) { handle_error = true;
- if (IS_ERR(tree_root->node)) + if (IS_ERR(tree_root->node)) { ret = PTR_ERR(tree_root->node); - else if (!extent_buffer_uptodate(tree_root->node)) + tree_root->node = NULL; + } else if (!extent_buffer_uptodate(tree_root->node)) { ret = -EUCLEAN; + }
btrfs_warn(fs_info, "failed to read tree root"); continue;