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btrfs: Avoid live-lock in search_ioctl() on hardware with sub-page faults

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Commit a48b73eca4 ("btrfs: fix potential deadlock in the search
ioctl") addressed a lockdep warning by pre-faulting the user pages and
attempting the copy_to_user_nofault() in an infinite loop. On
architectures like arm64 with MTE, an access may fault within a page at
a location different from what fault_in_writeable() probed. Since the
sk_offset is rewound to the previous struct btrfs_ioctl_search_header
boundary, there is no guaranteed forward progress and search_ioctl() may
live-lock.

Use fault_in_subpage_writeable() instead of fault_in_writeable() to
ensure the permission is checked at the right granularity (smaller than
PAGE_SIZE).

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Fixes: a48b73eca4 ("btrfs: fix potential deadlock in the search ioctl")
Reported-by: Al Viro <viro@zeniv.linux.org.uk>
Acked-by: David Sterba <dsterba@suse.com>
Cc: Chris Mason <clm@fb.com>
Cc: Josef Bacik <josef@toxicpanda.com>
Link: https://lore.kernel.org/r/20220423100751.1870771-4-catalin.marinas@arm.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
This commit is contained in:
Catalin Marinas 2022-04-23 11:07:51 +01:00
parent f3ba50a7a1
commit 18788e3464
1 changed files with 6 additions and 1 deletions
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7
fs/btrfs/ioctl.c
View file

@ -2565,7 +2565,12 @@ static noinline int search_ioctl(struct inode *inode,
while (1) {
ret = -EFAULT;
if (fault_in_writeable(ubuf + sk_offset, *buf_size - sk_offset))
/*
* Ensure that the whole user buffer is faulted in at sub-page
* granularity, otherwise the loop may live-lock.
*/
if (fault_in_subpage_writeable(ubuf + sk_offset,
*buf_size - sk_offset))
break;
ret = btrfs_search_forward(root, &key, path, sk->min_transid);