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author | Josef Bacik <josef@toxicpanda.com> | 2020-08-10 18:42:27 +0300 |
---|---|---|
committer | David Sterba <dsterba@suse.com> | 2020-08-27 14:56:27 +0300 |
commit | a48b73eca4ceb9b8a4b97f290a065335dbcd8a04 (patch) | |
tree | 29b424390a9bed80f10f38136cef48498c2a8f9b /fs | |
parent | 9771a5cf937129307d9f58922d60484d58ababe7 (diff) | |
download | linux-a48b73eca4ceb9b8a4b97f290a065335dbcd8a04.tar.xz |
btrfs: fix potential deadlock in the search ioctl
With the conversion of the tree locks to rwsem I got the following
lockdep splat:
======================================================
WARNING: possible circular locking dependency detected
5.8.0-rc7-00165-g04ec4da5f45f-dirty #922 Not tainted
------------------------------------------------------
compsize/11122 is trying to acquire lock:
ffff889fabca8768 (&mm->mmap_lock#2){++++}-{3:3}, at: __might_fault+0x3e/0x90
but task is already holding lock:
ffff889fe720fe40 (btrfs-fs-00){++++}-{3:3}, at: __btrfs_tree_read_lock+0x39/0x180
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #2 (btrfs-fs-00){++++}-{3:3}:
down_write_nested+0x3b/0x70
__btrfs_tree_lock+0x24/0x120
btrfs_search_slot+0x756/0x990
btrfs_lookup_inode+0x3a/0xb4
__btrfs_update_delayed_inode+0x93/0x270
btrfs_async_run_delayed_root+0x168/0x230
btrfs_work_helper+0xd4/0x570
process_one_work+0x2ad/0x5f0
worker_thread+0x3a/0x3d0
kthread+0x133/0x150
ret_from_fork+0x1f/0x30
-> #1 (&delayed_node->mutex){+.+.}-{3:3}:
__mutex_lock+0x9f/0x930
btrfs_delayed_update_inode+0x50/0x440
btrfs_update_inode+0x8a/0xf0
btrfs_dirty_inode+0x5b/0xd0
touch_atime+0xa1/0xd0
btrfs_file_mmap+0x3f/0x60
mmap_region+0x3a4/0x640
do_mmap+0x376/0x580
vm_mmap_pgoff+0xd5/0x120
ksys_mmap_pgoff+0x193/0x230
do_syscall_64+0x50/0x90
entry_SYSCALL_64_after_hwframe+0x44/0xa9
-> #0 (&mm->mmap_lock#2){++++}-{3:3}:
__lock_acquire+0x1272/0x2310
lock_acquire+0x9e/0x360
__might_fault+0x68/0x90
_copy_to_user+0x1e/0x80
copy_to_sk.isra.32+0x121/0x300
search_ioctl+0x106/0x200
btrfs_ioctl_tree_search_v2+0x7b/0xf0
btrfs_ioctl+0x106f/0x30a0
ksys_ioctl+0x83/0xc0
__x64_sys_ioctl+0x16/0x20
do_syscall_64+0x50/0x90
entry_SYSCALL_64_after_hwframe+0x44/0xa9
other info that might help us debug this:
Chain exists of:
&mm->mmap_lock#2 --> &delayed_node->mutex --> btrfs-fs-00
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(btrfs-fs-00);
lock(&delayed_node->mutex);
lock(btrfs-fs-00);
lock(&mm->mmap_lock#2);
*** DEADLOCK ***
1 lock held by compsize/11122:
#0: ffff889fe720fe40 (btrfs-fs-00){++++}-{3:3}, at: __btrfs_tree_read_lock+0x39/0x180
stack backtrace:
CPU: 17 PID: 11122 Comm: compsize Kdump: loaded Not tainted 5.8.0-rc7-00165-g04ec4da5f45f-dirty #922
Hardware name: Quanta Tioga Pass Single Side 01-0030993006/Tioga Pass Single Side, BIOS F08_3A18 12/20/2018
Call Trace:
dump_stack+0x78/0xa0
check_noncircular+0x165/0x180
__lock_acquire+0x1272/0x2310
lock_acquire+0x9e/0x360
? __might_fault+0x3e/0x90
? find_held_lock+0x72/0x90
__might_fault+0x68/0x90
? __might_fault+0x3e/0x90
_copy_to_user+0x1e/0x80
copy_to_sk.isra.32+0x121/0x300
? btrfs_search_forward+0x2a6/0x360
search_ioctl+0x106/0x200
btrfs_ioctl_tree_search_v2+0x7b/0xf0
btrfs_ioctl+0x106f/0x30a0
? __do_sys_newfstat+0x5a/0x70
? ksys_ioctl+0x83/0xc0
ksys_ioctl+0x83/0xc0
__x64_sys_ioctl+0x16/0x20
do_syscall_64+0x50/0x90
entry_SYSCALL_64_after_hwframe+0x44/0xa9
The problem is we're doing a copy_to_user() while holding tree locks,
which can deadlock if we have to do a page fault for the copy_to_user().
This exists even without my locking changes, so it needs to be fixed.
Rework the search ioctl to do the pre-fault and then
copy_to_user_nofault for the copying.
CC: stable@vger.kernel.org # 4.4+
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Diffstat (limited to 'fs')
-rw-r--r-- | fs/btrfs/extent_io.c | 8 | ||||
-rw-r--r-- | fs/btrfs/extent_io.h | 6 | ||||
-rw-r--r-- | fs/btrfs/ioctl.c | 27 |
3 files changed, 27 insertions, 14 deletions
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c index 617ea38e6fd7..c15ab6c1897f 100644 --- a/fs/btrfs/extent_io.c +++ b/fs/btrfs/extent_io.c @@ -5653,9 +5653,9 @@ void read_extent_buffer(const struct extent_buffer *eb, void *dstv, } } -int read_extent_buffer_to_user(const struct extent_buffer *eb, - void __user *dstv, - unsigned long start, unsigned long len) +int read_extent_buffer_to_user_nofault(const struct extent_buffer *eb, + void __user *dstv, + unsigned long start, unsigned long len) { size_t cur; size_t offset; @@ -5675,7 +5675,7 @@ int read_extent_buffer_to_user(const struct extent_buffer *eb, cur = min(len, (PAGE_SIZE - offset)); kaddr = page_address(page); - if (copy_to_user(dst, kaddr + offset, cur)) { + if (copy_to_user_nofault(dst, kaddr + offset, cur)) { ret = -EFAULT; break; } diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h index 00a88f2eb5ab..30794ae58498 100644 --- a/fs/btrfs/extent_io.h +++ b/fs/btrfs/extent_io.h @@ -241,9 +241,9 @@ int memcmp_extent_buffer(const struct extent_buffer *eb, const void *ptrv, void read_extent_buffer(const struct extent_buffer *eb, void *dst, unsigned long start, unsigned long len); -int read_extent_buffer_to_user(const struct extent_buffer *eb, - void __user *dst, unsigned long start, - unsigned long len); +int read_extent_buffer_to_user_nofault(const struct extent_buffer *eb, + void __user *dst, unsigned long start, + unsigned long len); void write_extent_buffer_fsid(const struct extent_buffer *eb, const void *src); void write_extent_buffer_chunk_tree_uuid(const struct extent_buffer *eb, const void *src); diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c index bd3511c5ca81..ac45f022b495 100644 --- a/fs/btrfs/ioctl.c +++ b/fs/btrfs/ioctl.c @@ -2086,9 +2086,14 @@ static noinline int copy_to_sk(struct btrfs_path *path, sh.len = item_len; sh.transid = found_transid; - /* copy search result header */ - if (copy_to_user(ubuf + *sk_offset, &sh, sizeof(sh))) { - ret = -EFAULT; + /* + * Copy search result header. If we fault then loop again so we + * can fault in the pages and -EFAULT there if there's a + * problem. Otherwise we'll fault and then copy the buffer in + * properly this next time through + */ + if (copy_to_user_nofault(ubuf + *sk_offset, &sh, sizeof(sh))) { + ret = 0; goto out; } @@ -2096,10 +2101,14 @@ static noinline int copy_to_sk(struct btrfs_path *path, if (item_len) { char __user *up = ubuf + *sk_offset; - /* copy the item */ - if (read_extent_buffer_to_user(leaf, up, - item_off, item_len)) { - ret = -EFAULT; + /* + * Copy the item, same behavior as above, but reset the + * * sk_offset so we copy the full thing again. + */ + if (read_extent_buffer_to_user_nofault(leaf, up, + item_off, item_len)) { + ret = 0; + *sk_offset -= sizeof(sh); goto out; } @@ -2184,6 +2193,10 @@ static noinline int search_ioctl(struct inode *inode, key.offset = sk->min_offset; while (1) { + ret = fault_in_pages_writeable(ubuf, *buf_size - sk_offset); + if (ret) + break; + ret = btrfs_search_forward(root, &key, path, sk->min_transid); if (ret != 0) { if (ret > 0) |