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authorJosef Bacik <josef@toxicpanda.com>2020-08-10 11:42:27 -0400
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2020-09-09 19:04:29 +0200
commit7c9bf5c3ed15fd6ad777663c636a6f4a5d9edf2c (patch)
tree5b8c2813f68ba499fee23d019950d570e1853b22
parentcfb4721fce554cb596ea86af116d3d68a4d91254 (diff)
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btrfs: fix potential deadlock in the search ioctl
[ Upstream commit a48b73eca4ceb9b8a4b97f290a065335dbcd8a04 ] 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> Signed-off-by: Sasha Levin <sashal@kernel.org>
-rw-r--r--fs/btrfs/extent_io.c8
-rw-r--r--fs/btrfs/extent_io.h6
-rw-r--r--fs/btrfs/ioctl.c27
3 files changed, 27 insertions, 14 deletions
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index fbcd18d96c52..82d597b16152 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -5377,9 +5377,9 @@ 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;
@@ -5400,7 +5400,7 @@ 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 (probe_user_write(dst, kaddr + offset, cur)) {
ret = -EFAULT;
break;
}
diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h
index a3598b24441e..d5089cadd7c4 100644
--- a/fs/btrfs/extent_io.h
+++ b/fs/btrfs/extent_io.h
@@ -448,9 +448,9 @@ 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(struct extent_buffer *eb, const void *src);
void write_extent_buffer_chunk_tree_uuid(struct extent_buffer *eb,
const void *src);
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index a5ae02bf3652..85990755edd9 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -2079,9 +2079,14 @@ 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 (probe_user_write(ubuf + *sk_offset, &sh, sizeof(sh))) {
+ ret = 0;
goto out;
}
@@ -2089,10 +2094,14 @@ 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;
}
@@ -2180,6 +2189,10 @@ 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)